perm filename CLWIND.MSG[COM,LSP]5 blob sn#782733 filedate 1985-01-09 generic text, type C, neo UTF8
C00001 00001
C00002 00002	Introduction
C00005 ENDMK
Welcome to the Common Lisp Window Subgroup.
In order to mail to this group, send to the address:

Capitalization is not necessary, and if you are directly on the ARPANET,
you can nickname SU-AI.ARPA as SAIL. An archive of messages is kept on
SAIL in the file:


You can read this file or FTP it away without logging in to SAIL.

To communicate with the moderator, send to the address:

Here is a list of the people who are currently on the mailing list:

Person			Affiliation	Net Address

Kent Pitman		MIT		kmp@mc
Dick Gabriel		Stanford/Lucid	rpg@sail
Carl Hewitt		MIT		hewitt-windows@mc
Don Allen		BBN		allen@bbnf
Dan Oldman		Data General	not established
Larry Stabile		Apollo		not established
Tom Kaczuarek		ISI		kaczuarek@isi
Dave Matthews		HP		matthews.hplabs@csnet-relay (I hope)
Dan Stenger		TI		stenger.ti-csl@csnet-relay
Gary Brown		DEC		gbrown@dec-marlboro
Joe Ginder		PERQ		Joseph.Ginder@cmu-cs-spice
Thomas Gruber		Univ. of Mass.	gruber.UMass-CS@csnet-relay

The first order of business is for each of us to ask people we know who may
be interested in this subgroup if they would like to be added to this list.

Next, we ought to consider who might wish to be the chairman of this subgroup.
Before this happens, I think we ought to wait until the list is more nearly

∂23-Sep-84  1610	RPG  	Introduction  
To:   cl-windows@SU-AI.ARPA 
Welcome to the Common Lisp Window Subgroup.
In order to mail to this group, send to the address:

Capitalization is not necessary, and if you are directly on the ARPANET,
you can nickname SU-AI.ARPA as SAIL. An archive of messages is kept on
SAIL in the file:


You can read this file or FTP it away without logging in to SAIL.

To communicate with the moderator, send to the address:

Here is a list of the people who are currently on the mailing list:

Person			Affiliation	Net Address

Kent Pitman		MIT		kmp@mc
Dick Gabriel		Stanford/Lucid	rpg@sail
Carl Hewitt		MIT		hewitt-windows@mc
Don Allen		BBN		allen@bbnf
Dan Oldman		Data General	not established
Larry Stabile		Apollo		not established
Tom Kaczuarek		ISI		kaczuarek@isi
Dave Matthews		HP		matthews.hplabs@csnet-relay (I hope)
Dan Stenger		TI		stenger.ti-csl@csnet-relay
Gary Brown		DEC		gbrown@dec-marlboro
Joe Ginder		PERQ		Joseph.Ginder@cmu-cs-spice
Thomas Gruber		Univ. of Mass.	gruber.UMass-CS@csnet-relay

The first order of business is for each of us to ask people we know who may
be interested in this subgroup if they would like to be added to this list.

Next, we ought to consider who might wish to be the chairman of this subgroup.
Before this happens, I think we ought to wait until the list is more nearly

∂02-Oct-84  1311	RPG  	Chairman 
To:   cl-windows@SU-AI.ARPA 
Now that we've basically got most everyone who is interested on the mailing
list, let's pick a chairman. I suggest that people volunteer for chairman.

The duties are to keep the discussion going, to gather proposals and review
them, and to otherwise administer the needs of the mailing list. I will
retain the duties of maintaining the list itself and the archives, but
otherwise the chairman will be running the show. 

Any takers?

∂13-Oct-84  1440	RPG  	Chairman 
To:   cl-windows@SU-AI.ARPA 

No one has been nominated as chairman of the Windows subgroup.  I
suggest Howard Cannon of Symbolics. If he is willing, and no one else
volunteers, he will become chairman. Please respond by October 24. At the
end of this month I want to see some ideas and proposals coming in on this
mailing list.


∂25-Oct-84  0944	FILE-SERVER%WHITE.SWW.Symbolics@SCRC-RIVERSIDE.ARPA 	Chairman    
Received: from SCRC-QUABBIN.ARPA by SU-AI.ARPA with TCP; 25 Oct 84  09:43:40 PDT
Received: from SWW-WHITE by SCRC-QUABBIN via CHAOS with CHAOS-MAIL id 94510; Tue 23-Oct-84 23:01:25-EDT
Date: Tue, 23 Oct 84 20:06 PDT
Subject: Chairman 
To: RPG@SU-AI.ARPA, cl-windows@SU-AI.ARPA
In-reply-to: The message of 13 Oct 84 14:40-PDT from Dick Gabriel <RPG at SU-AI>

    Received: from SCRC-STONY-BROOK by SWW-WHITE via CHAOS with CHAOS-MAIL id 47648; Sat 13-Oct-84 15:37:52-PDT
    Received: from MIT-MC by SCRC-STONY-BROOK via CHAOS with CHAOS-MAIL id 107864; Sat 13-Oct-84 18:32:38-EDT
    Date: 13 Oct 84  1440 PDT
    From: Dick Gabriel <RPG@SU-AI.ARPA>
    Subject: Chairman 
    To:   cl-windows@SU-AI.ARPA 

    No one has been nominated as chairman of the Windows subgroup.  I
    suggest Howard Cannon of Symbolics. If he is willing, and no one else
    volunteers, he will become chairman. Please respond by October 24. At the
    end of this month I want to see some ideas and proposals coming in on this
    mailing list.


Ah, I see I received this message.  I was worried that this mail wasn't
getting through, or was stuck at MC, or...

In any case, I respectfully decline the offer, not because I don't want
to do it but because of extensive traveling I don't feel I could be
reliable enough.  I do hope to participate actively, though.

I suggest that DDYER would do a fine job as chairman.


∂27-Oct-84  2148	RPG  	Hello folks   
To:   cl-windows@SU-AI.ARPA 

We now have a chairman of the windows subgroup:  Dave Dyer of Symbolics. I
think he will make an excellent chairman.  For your information I am
including the current members of the mailing list.

I will now let Dave Dyer take over responsibility for the discussion.

David Matthews		HP		"hpfclp!windows%hplabs"@csnet-relay,
Jerry Boetje		DEC		Boetje@dec-hudson
John Foderaro		Berkeley
Steve Muchnick		SUN		"ucbvax!sun!muchnick"@berkeley
Howard Cannon		Symbolics 	"hic%scrc"@mc
Dave Dyer		Symbolics	ddyer@isib
Skef Wholey		CMU		Wholey@cmuc
Richard Zippel		MIT		rz@mc
Ron MacLachlan		CMU		RAM@cmu-cs-c
John Peterson		Univ of Utah	jw-peterson@utah-20
Kent Pitman		MIT		kmp@mc
Dick Gabriel		Stanford/Lucid	rpg@sail
Carl Hewitt		MIT		hewitt-windows@mc
Don Allen		BBN		allen@bbnf
Dan Oldman		Data General	not established
Larry Stabile		Apollo		not established
Tom Kaczmarek		ISI		kaczmarek@isi
Dan Stenger		TI		stenger.ti-csl@csnet-relay
Gary Brown		DEC		brown@dec-hudson
Joe Ginder		PERQ		Joseph.Ginder@cmu-cs-spice
Thomas Gruber		Univ. of Mass.	gruber.UMass-CS@csnet-relay
Ron Fischer		Rutgers		fischer@rutgers
Dario Giuse		CMU		dzg@cmu-cs-spice
Neal Feinberg		Symbolics	feinberg@scrc-stony-brook

∂28-Oct-84  1054	DDYER@USC-ISIB.ARPA 	Initial questions  
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 28 Oct 84  10:53:57 PST
Date: 28 Oct 1984 10:52:38 PST
Subject: Initial questions
From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
To: cl-windows@SU-AI.ARPA

Ok, since I have no idea what I'm supposed to do, I'll
just do what comes naturally.   What is the scope of
this discussion?  These questions come to mind:

What kinds of window hardware are we talking about?  Plain
glass ttys?  Bitmapped?  Vector?  Color?

What implementation technology?  Particularly, will we use
whatever the CL standard for objects becomes, or structures.

Fonts?  Text formatting?   What is the boundary between 
this mailing list and what "graphics" will discuss.

What about pointing devices?

∂29-Oct-84  0917	DDYER@USC-ISIB.ARPA 	Initial Answer
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 29 Oct 84  09:17:19 PST
Date: 29 Oct 1984 09:12:53 PST
Subject: Initial Answer
From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
To: cl-windows@SU-AI.ARPA

[ Editors Note:  Since this reply came to me rather than the mailing list,
  I am reminded of the perpetual question;  "To Digest or not to Digest"
  For now, I will package any replies that come directly to me, and send
  them to the mailing list from time to time.   Messages sent to 
  cl-windows@su-ai will continue to be redistributed immediately.

Date: 29 Oct 1984 07:47:00 PST
Subject: Re: Initial questions

Regarding interaction with the graphics group, I think we ought to try to 
build on top of what they supply.  I suspect that there is enough cross-
membership to insure that we have sufficient influence.  (I haven't compared
the mailing lists so I could be wrong about that.)

[ddyer: I tend to look at it the other way; Graphics is an additional
 behavior of windows, and graphics capabilities will be built out of
 whatever we supply.]

As far as display hardware goes there seems to be two interesting classes--
"graphics" and glass ttys.  Color is an orthogonal issue, isn't it?
Number of bit planes for black and white graphics falls in this same
category.  Both graphic devices and ttys come in black and white (with
intensity levels) or color.  Graceful degradation seems to be the
appropriate way to handle these issues.  I believe the graphics people
having been looking at this issue for some time and have solutions for this

I would guess that if the graphics group does its job well, vector versus
bitmapped graphics should not be an issue.  The resolution of the graphics
may be an issue however.  Low resolution graphics devices seem a lot like
glass ttys as far as windows go.  Storage vector graphics hardware (ala
old Tektronix stuff) does not lend itself to the kind of interaction one
expects from a window system so I think we can eliminate it.  I believe the
graphics group also should make pointing devices less of a problem since
graphics standards have abstracted actions like "picking."  I believe that
complex mouse buttoning will still be something of a problem.

Structures versus objects seems to be a difficult decision.  Perhaps having
to wait for a object standard will be the best argument for structures.
Conceptually, objects are nice for the kind of interactions that occur in
the window world.  Is efficiency an issue here?  Object-oriented
implementations seems to rely on interpretation rather than compilation.
Is that because nobody has done it differently or is it too hard?  Or
impossible?  Or am I wrong about that?

[ddyer: flavors are compiled]

∂29-Oct-84  1045	boetje@DEC-HUDSON 	some initial answers(?)   
Received: from DEC-HUDSON.ARPA by SU-AI.ARPA with TCP; 29 Oct 84  10:43:09 PST
Date: Mon, 29 Oct 84 13:39:39 EST
From: boetje@DEC-HUDSON
Subject: some initial answers(?)

Ok, it's Monday morning and I'm ready to take on windows. This note is in 
direct reply to Dave Dyer's set of questions over the weekend. 

Let's take the terminology question first. I have a strong feeling that we 
need to get this handled before much else can happen. One of the major 
difficulties in this area is that there seem to be two different views of what 
the term "window" refers to. Most everyone working on bitmapped screens these 
days calls the funny rectangular areas (with borders and labels, in which you 
can put text or draw lines) windows. The graphics community uses "window" in a 
very different way. A window is really a way to specify a set of coordinate 
transformations and a set of bounding coordinates for clipping purposes. You 
can't ever see a graphics window. It takes a viewport to make that happen. 
Viewports are potentially viewable objects. But of course in that graphics 
world, there isn't a firm concept of borders and labels.

I will put forth the following radical suggestion: the graphics folks were 
here first, so their terminology should take precedence. Windows and viewports 
are strictly defined in the world of real graphics. A window is a set of 
limiting coordinates (x-y min and max values) in some arbitrary system
(usually the coordinate system of the data values to be plotted). This defines 
the aspect ratio of the eventual display of data. A viewport is another set of 
limiting coordinates which are used to map the data plotted in coordinates of 
the window to a displayable rectangle (this provides for clipping, 
magnification, and transformation to the physical device).So we won't do 
windows (sorry about the marketing slogan). We need to call those funny 
rectangles on the screen something else.

Before I unveil my terms, let me introduce a concept into this arena. In both 
the graphics world and whatever-we-call-the-current-thing world, there is the 
idea of a displayable object. In the graphics world, viewports can be 
displayable objects (when they map things from NDC space for example). They 
can also be previously created "pictures" which can be used to make composite 
images (for example, the symbol for a NAND gate in a CAD system). The common 
term for this object is "segment". Segments can be replicated and scaled ad 
nauseum to make a larger displayable object. The graphics world thus has a 
model of composition by using displayable objects as well as basic line 
drawing primitives.

In the bitmapped world, "windows"  are considered displayable objects. In the
case of Symbolics, they also  provide the idea of decomposition of their window
into "panes" (which can be  treated as individual windows for many purposes).
Another way of looking at  their system is that they treat their "window" as a
displayable object which can be composed of other windows. Their composition 
process also involves a particular contraint system on the interaction between 
the parts of a composed displayable object (resize one and the others adjust).

With all that said, I now introduce my own terms (liberally borrowed from 
unnamed sources):

1. Virtual Display. This is what most folks think of as a "window" or perhaps
a bitmap (depending on whether it's visible or not). You may see it (touch it
and taste it if it's late enough at night) on the screen. It's a  rectangular
area which may be made to appear on a physical display (hence the term virtual
display) which  can have a border, a label, etc. Primitive operations can put
information into  the display (like writing characters or drawing lines). If
they are not currently visible on the physical display, their current state is
kept and  modified by primitive operations. 

They can also be  composed of other virtual displays with appropriate
constraints at the whim of the implemectation. It may or may not be on the
physical display and it may or  may not be hidden obscured by other visible
displays). It can function as an I/O device for CL streams. And if you're into
the graphics side of the world, viewports map directly into the non-border
portion of virtual displays.  

2. Windows and viewports retain (and will only be used for describing) their 
traditional meanings in the world of graphics (which among other things means 
that windows and viewports operate in coordinate systems other than that of 
the physical display device).

3. Displayable object. Well, I gave the sense of it above. If we want to 
strictly define it for CL, then we'll need to do some work on it. I'm inclined 
to leave it alone for now and just use it by way of introducing concepts of 
composition. We'd need to be very closely tied to the graphics folks if we 
want to define it in the language.

Ok, enough on terms. Hardware... hmm... Curiously, the most limiting hardware 
is the vector drawing equipment, because it's hard to change once you've put 
it on the screen. My thought is that we should at least define operations that 
can be done on a cell-oriented screen. We can define optional capabilities for 
displays, but that gets us into the serious business of specifying how the 
user program determines the capabilities that can be used on the runtime 
device and what the error mechanism is for operations that can't be supported 
on the current device. The GKS graphics folks have done this and the inquiry 
functions outnumber the primitive operations.

On the software implementation, we should go for the least disruptive and 
commonly implemented features (GCLISP has some nice display stuff on a small 
machine). I think this means structures, not objects. We might want to define 
an optional object interface to the displays, but I think we need the simple 
level as well. Also, I don't want to wait around for the religious wars over 
objects. We'll have enough of our own...

Fonts, et al. Ok, we need some optional ways to specify font information and 
it's not clear that font bits are the best way to go. VAX LISP would probably 
have a difficult time handling font information in strings (efficient strings 
for us are one byte per character). Font information should be an ignoreable 
parameter (VT200's don't do well when commanded to go into Times Roman). 
Having a function that computes the actual screen size of a string in a 
specified font is a must.

Text formatting. We need text primitives to write, erase and insert 
characters. But I'm not anxious to get into the business of putting Scribe 
into CL. But there should be enough functionality for the cottage industries 
to write a formatting system on top of the CL primitives.

Boundary between this group and graphics. Ok, I've got a foot in both, so I'll 
jump in. We should stick to the ideas of virtual displays and composition of 
virtual displays. They should always operate in the coordinate system of the 
device. The graphics world should get windows, viewports and segments and 
operate in non-device coordinates. Our major interface then becomes a mapping 
of viewport to virtual display with the graphics side worrying about the 
scaling and clipping into the device (virtual display) coordinates.

Last topic for now... pointing devices. hmmm. They're needed for two purposes,
at least. One is to do operations on entire virtual displays (like popping
them to the surface). They other is to indicate a point or segment within a
virtual display. These operations can be handled with mouses and tablets and
can be simulated with cursor keys. We have to be careful not to get into the
business of defining a user interface to CL (pointing at a label brings a
display to the surface). But it would be nice to have some simple functions to
let users roll their own. 

Indicating a point or segment is a bit more interesting and gets us involved 
with the graphics group. Points within a virtual display need to be returned 
in some coordinate system. Most bitmap systems give back a point in raster 
coordinates. That's probably limiting. The graphics world likes them returned 
in the original coordinates used to draw the picture. And picking graphics 
segments has a close counterpart in defining/selecting a sensitive region.
Topic for next time.

Oh yes, color. Pick and stick to one of the international standards. There's 
RGB (red, green, blue) and HLS (hue, lightness and saturation). Any of you 
VideoText folks probably have yet another way. I have no real preference (just 
a minor leaning to HLS) but I haven't figured out if I should grind an ax on 
this or not. Issue deferred...


∂30-Oct-84  0711 	Terminology, etc.
Received: from CMU-CS-SPICE.ARPA by SU-AI.ARPA with TCP; 30 Oct 84  07:10:20 PST
Date: Tuesday 30 October 1984 09:33:00am-EST
Subject: Terminology, etc.
Message-ID: <0.0.dzg>

I mostly agree with Jerry Boetje. Let's use "window" for a set of bounding
coordinates; the confusion in the bitmap world is hopeless anyway. As an
example, on the Perq a 'viewport' is a rectangular portion of a display, and
a 'window' is essentially a viewport embellished with borders and a
'title'; on the Symbolics, a 'window' is essentially a viewport that may or
may not have borders and a 'label' (title).

I have a little problem with the term "segment", just because it is so
overloaded. I would try and suggest "symbol", a' la Newman & Sproull, just
because it's nice to talk about a symbol and a symbol instance. I realize,
though, that the word "symbol" is also overloaded...
One related question is transformations: can you only specify a
transformation (rotation, scale, offset) for symbols|segments, or can you
transform any graphical object in place?  Do you want to be able to say
"This is an arc of a circle, center and radius such and such, and by the
way it is scaled up 3.2 and rotated pi radians"?  Or do you always have to
wrap the arc in a symbol|segment to achieve the same effect? 

I also agree that we should use the universally available Structures for
the software implementation, given that no universally accepted (or
implemented!) notion of object seems to be around the corner. The BIG
problem, here, is that if you are not very careful your structures turn out
to be a "display list" that the system maintains, and so you have to
duplicate them all to put the interesting stuff you want to deal with. One
of the ideas I am trying to work on is to SHARE your data structures with
the system, so that you can have all the nice slots you want in there that
are not graphical at all, while the system can store all its internal cute
optimization things in it. This is unfortunately difficult to do with
structures a' la DefStruct, since the slots are defined once and for all.
An object system would be much nicer, since the system can define all its
nasty things and you never need to know about them.

Fonts: the "best approximation" paradigm should apply. My approach would be
to have a very generic font definition (family name, face, size, rotation)
which would be mapped into whatever the system provides. Font names are
totally hopeless (What's a CPT10? Is it 10 points or 10 pixels? Or is it
the 10th font in the file CPT? And what's a CPT anyway?), so I think one
would end up having a device-dependent mapping between an "abstract font"
and whatever the system provides. The mapping would be very dull on the
VT200, for instance, but one should use an abstract specification

I very strongly oppose any notion of text formatting. Only the very minimal
level of support, including obviously the ability to get device-dependent
font information (IN WORLD COORDINATES, not in device coordinates!), should
be present. More complex text formatting is A) highly dependent on personal
taste, and B) extremely difficult to do right for sophisticated
applications. I certainly don't want a window system at this level to have
to deal with kerning and italic corrections.

  - Dario -

∂31-Oct-84  0723 	re: inital answers   
Received: from CSNET-RELAY.ARPA by SU-AI.ARPA with TCP; 31 Oct 84  07:23:51 PST
Received: from ti-csl by csnet-relay.csnet id ad00735; 31 Oct 84 10:18 EST
Date: 31 Oct 1984 0625-CST
From: Dan Stenger <>
Subject: re: inital answers
Received: from csl60 by ti-csl; Wed, 31 Oct 84 09:13 CST

On terminology:
I agree with Jerry Boetje's proposal on the terminology that we should use.
We should settle on something so that we all understand each other.  The
main problem I see with this is that the terms "windows" and "panes" are
well established in the Lisp community and we may just cause confusion.

On bounds of this group:
I am also in the graphics group.  My view is that we should limit the
efforts of the windows group to virtual displays and other things that
need to work in device coordinates.  The graphics group should handle
what is shown in the virtual displays.

On the software implementation:
I agree that structures are the way to go.  Some implementations may not
want the object oriented programming system but may want windows.  Also
the wait may just put us too far behind.

On display hardware:
It would be nice if what we come up with is compatible with vector refresh
and storage tube hardware but I do not think that we should concern ourselves
with it.  The types of hardware which we do need to address are black/white
and color bitmaped terminals, and text only terminals.

In general I think we should try to design something that is concise, simple,
but very general.  It should be implementable on small machines but be easily
extended (not restrictive) for larger machines.

		Dan Stenger

∂02-Nov-84  2330	DDYER@USC-ISIB.ARPA 	Real devices (mainly)   
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 2 Nov 84  23:30:41 PST
Date:  2 Nov 1984 23:26:10 PST
Subject: Real devices (mainly)
From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
To: cl-windows@SU-AI.ARPA

There seems to be consensus that vector displays are outside
our domain.  If there are no devotees of vector displays out
out there, I'll consider it official.

I liked "virtual display", but one term isn't a complete glossary.

  Several messages have cast a word in favor of supporting ordinary
terminals; but I wonder just how much one can do, especially if
"virtual display" is taken to imply "multiple virtual displays".
In practice, won't terminals be restricted to one or two virtual
displays, all the same width as the screen?   I've done quite
a bit of display hacking on ordinary terminals, and found anything
fancier to be aesthtically awful, even if technically possible.

  There simply isn't enough real estate to distinguish more than
a few windows, aren't display capabilities to provide margins
and borders, and the devices themselves don't operate fast or
reliably enough to allow manipulation of arbitrary blocks of
characters in a way that is acceptable to users.   Shouldn't we
take this ugly bit of reality into account? 

  I'm not necessarily proposing we punt terminals entirely, but
we should at least consider defining a limited set of primitives 
for terminals sufficient for input editing and (maybe) emacs style

  I also have doubts about several mentions of "device coordinates"
as the appropriate substrate for virtual displays.   One at least
needs to be able to speak of either "characters" or "pixels", to
accommodate ordinary terminals and bitmaps, but once pixels are
introduced, a whole nest of other problems surface; such as
aspect ratio, variable width and height of fonts, and the variable
size of pixels on different displays.  

  For a particular display, one could of course tweak things into
the right device coordinates to give the desired effect, but we
are speaking "portable" here, so need to at least address the question
of transmitting the author's intent to foreign systems.   

  Just to finish on a concrete point, consider Symbolic's color
displays, where the "same size" characters (in device coordinates)
border on unreadable compared to the same text on the B&W screen.   
Also, consider that a single pixel height horizontal line on a
noninterlaced screen is fine, but on an interlaced screen it is
probably unacceptable due to excess flicker.

  No program that operates in "device" coordinates can ignore facts
of life such as these.  We need to strike a balance between providing 
access to the raw facts, and hoping programs cope with all the possible
implications, and attempting to abstract intent into our specs and letting
the implementation cope with the ramifications.


∂03-Nov-84  0747	FAHLMAN@CMU-CS-C.ARPA 	Goals  
Received: from CMU-CS-C.ARPA by SU-AI.ARPA with TCP; 3 Nov 84  07:47:49 PST
Received: ID <FAHLMAN@CMU-CS-C.ARPA>; Sat 3 Nov 84 10:47:55-EST
Date: Sat, 3 Nov 1984  10:47 EST
Message-ID: <FAHLMAN.12060631562.BABYL@CMU-CS-C.ARPA>
From: "Scott E. Fahlman" <Fahlman@CMU-CS-C.ARPA>
To:   cl-windows@SU-AI.ARPA
Subject: Goals

In my opinion, the window group is really in the business of developing
one or more optional semi-standards.  What I mean by that is that I
don't think that the Common Lisp specification should require any
particular sort of display or window system in order for something to be
called Common Lisp.  Display technology is moving pretty fast, and we
wouldn't want to rule out a Common Lisp in a wristwatch or a Common Lisp
running on a brute-force machine with no display of its own.
Furthermore, each machine running Common Lisp will have a few
specialized high-performance tricks available that users will want to
access for the most demanding applications: one machine might have a
hardware font and vector generator, another might have an incredibly
smart rasterop, and so on.  

But what we can and should do is to develop one or more clean interfaces
for doing some collection of popular things on certain popular families
of display technologies.  Implementors will be encouraged to provide
these standard interfaces on their machines wherever they make sense,
and people developing display-oriented code will then have the option of
writing it using the portable interface, for easy portability across a
class of machines, or of writing it to make the best possible use of a
given machine using whatever tense non-standard mechanisms may be

It seems to me that three families of display device are going to be
important in the near future: 24x80 character terminals with varying
degrees of crude graphics support, high-resolution (at least 600 x
800) monochrome bit-mapped displays with some sort of pointing device,
and high-res bit-mapped displays with color.  Rather than ruin the
interface we develop for bit-mapped displays by trying too hard to make
it all work on ASCII terminals, I propose that we define three separate

Level 1: Can be implemented on the majority of ASCII termianls.
Level 2: Assumes bit-mapped graphics, reasonable resolution, and a
Level 3: Same as above, but with color.

Software developers can target their software to raw common Lisp or to
any of these levels, depending on the capability they need and the
market they wish to address, or they can go native on a single
machine/system.  Maybe levels 2 and 3 can be collapsed into one.
This is set up as a sort of hierarchy, since I am assuming that any
machine providing level 2 support will also provide level 1 support and
so on.  But the situation is really not hierarchical -- one might
imagine vector displays as wanting a different kind of interface

The most important need right now is to come up with something for level
2, since the vast majority of Common Lisp implementations (not weighted
by number of users) is on machines of this class.

-- Scott

∂04-Nov-84  1816	JW-PETERSON@UTAH-20.ARPA 	Some responses...  
Received: from UTAH-20.ARPA by SU-AI.ARPA with TCP; 4 Nov 84  18:16:37 PST
Date: Sun 4 Nov 84 19:16:54-MST
From: John W. Peterson <JW-Peterson@UTAH-20.ARPA>
Subject: Some responses...
To: cl-windows@SU-AI.ARPA

VT100's.  The 24x80 terminal may not be dead, but is quickly dying.  A
reasonably intelligent bitmapped terminal with a mouse runs around $2K, and
will shortly drop to the VT100 [& clones] price range - this seems like a
good "lowest common denominator" level.

Fonts.  The discussion of fonts and formatting brings up an interesting
analogy: When the world migrated from TTY's to CRT's, many programs broke
(or just "looked ugly") because they couldn't deal with lower case input or
output.  The same sort of thing appears to be happening again, only this
time things are breaking (or just not looking right) because they can't deal
with multiple fonts - particularly ones with proportional spacing.  Having
at least some formatting facilities inherent in the window system (e.g., tab
stops that work correctly with proportional spaced fonts) would make the
programmer's life noticeably easier.

Units of measure.  Is anything wrong with measuring things in Pixels?  It
makes life much, much simpler (both conceptually and pragmatically) to
define screen coordinates in pixel units.  There is nothing very "display
specific" about pixel units of measure, particularly when you consider
"Virtual Displays" are usually of various sizes on the same screen.  As long
as we use digital computers, screens will be measured in discrete units -
both graphics and window packages might as well behave the same way.
(An interesting discussion of this is presented in "A Language for Bitmap
Manipulation" by Guibas & Stolfi in the July '82 Transactions on Graphics.)

∂19-Nov-84  0019	DDYER@USC-ISIB.ARPA 	Proposals and questions 
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 19 Nov 84  00:19:31 PST
Date: 19 Nov 1984 00:18:26 PST
Subject: Proposals and questions
From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
To: cl-windows@SU-AI.ARPA

I like Scott Fahlman's notion of defining two sets
of protocols, one for simple terminals and the other
for rasters.  Presumably the terminal protocol would
use characters and lines as its units, while the
raster protocol would use either characters or pixels.

Are there any existing standards we might use as a
starting point?   I'm hoping for something more abstract
than the lisp machine window system manual!  The first 
proposal circulated is likely to become the de facto standard.

In accordance with the above, I suggest the following

Each virtual display divides the world into three parts,

INSIDE a virtual display, two protocol sets are defined,
a "character oriented set" and a "raster oriented set".
The character oriented set deals with size, positioning,
font and other characteristics of characters.  The
raster oriented protocol also addresses characters,
but also any other graphics and display primitives.
It is permitted for an implementation to implement only
the character oriented protocol.

OUTSIDE a virtual display, protocols deal with its
size, position, visibility and so on with respect to
its superior.

I'm not sure how to encapsulate the notion of BORDERS
succinctly.  The best I can think of at the moment
is that borders are a specialization of the more general
notion of "clipping region"; that a window is defined
by a clipped region within its superior, and may
in turn define an inferior clipping region.


I'm personally a little worried by the consensus to implement
virtual displays using structures.  By way of bringing my
concerns to the surface, I'll pose a question:

 How much user extensibility to window system behavior will be
expected/permitted, and how will the data structure and procedural
hooks for that extensibility be supported?

 I think it is important that extensibility be a goal, and that
"extended" windows (oops! virtual displays!) be as well integrated
and as efficiently implemented as the system's supplied windows.
I know how to do this in an object oriented window system.  Tell me
how you'll do it in a structure based system.


∂19-Nov-84  2035	WHOLEY@CMU-CS-C.ARPA 	Proposals and questions
Received: from CMU-CS-C.ARPA by SU-AI.ARPA with TCP; 19 Nov 84  20:34:25 PST
Received: ID <WHOLEY@CMU-CS-C.ARPA>; Mon 19 Nov 84 23:33:14-EST
Date: Mon, 19 Nov 1984  23:33 EST
Message-ID: <WHOLEY.12064965182.BABYL@CMU-CS-C.ARPA>
From: Skef Wholey <Wholey@CMU-CS-C.ARPA>
To:   Cl-Windows@SU-AI.ARPA
Subject: Proposals and questions
In-reply-to: Msg of 19 Nov 1984  03:18-EST from Dave Dyer <DDYER at USC-ISIB.ARPA>

Here are some of my thoughts on "virtual displays," both their specification
and their implementation (via structures).

There are (currently) about three coarse levels in virtual display fanciness
that a virtual display system should try to support:
	Glass TTY with at least an addressable cursor (e.g. ADM-3A)
	"Smart" CRT terminal (e.g. Concept-100, VT-200)
	Bitmapped displays

I believe that any virtual display should support all operations (we have yet
to decide on the operations, but my point is that something like DELETE-CHAR
can be performed on any of the above, albeit with different performance).  Non-
bitmapped terminals could be treated as having 24 by 80 (or whatever) pixels,
and a 1 by 1 font.

The redisplay module of a text editor will want to use different screen update
algorithms depending on the sort of virtual display it is writing to.  Thus, a
virtual display should be able to provide information about the relative
efficiency of its operations.  At the very least, a programmer should be able
to find out in which of the three categories listed above a virtual display
belongs.  The editor's redisplay algorithm can then be tuned to the particular
output device.  The casual programmer could of course opt to ignore this extra
information.  The virtual display machinery could do all kinds of redisplay
optimization itself, but I believe that certain decisions are best made in the
client program.

Thus, the different "protocols" that Scott suggests would be kept at a level
below the virtual display operations, but programmers that wanted to could
easily figure out useful things about the implementation of a particular
virtual display.

We at CMU have had a good deal of success implementing streams with structures,
which leads me to believe that they'll be sufficient for implementing virtual
displays as well.  Our stream structures store both functions ("methods") and
data ("instance variables").  Common Lisp DEFSTRUCT provides inheritance
through the :INCLUDE option, which makes streams (somewhat) easily extensible.
I realize that this system is less flexible than one built on flavors (or any
other real object-oriented programming system), but it is highly portable, and
gives you 90% of the extensibility you'd ever want.

Thus, we might define a virtual display like this:

	(defstruct vd
	  "The root Virtual Display structure."
	  ;; Methods:
	  display-char				; Method for Display-char
	  display-string			; Method for Display-string
	  delete-char				; Method for Delete-Char
	  ;; Instance variables:
	  width					; Width in pixels
	  height				; Height in pixels
	  cursor-row				; Row that the cursor's on
	  cursor-column				; Column the cursor's on

	(defun display-char (vd char)
	  "Displays the Char at the current cursor position of the VD,
	   moving the cursor appropriately."
	  (funcall (vd-display-char vd) char))


Then we could define a particular kind of virtual display like this:

	(defstruct (c100-vd
		    (:include vd
			      (display-char c100-vd-display-char)
			      (display-string c100-vd-display-string)
	  "The VD for Concept-100 terminals."
	  ;; Additional instance variables:

	(defun c100-vd-display-char (vd char)
	  (write-char (c100-vd-stream vd) char)
	  (cond ((char= char #\newline)
		 (setf (vd-cursor-column vd) 0)
		 (incf (vd-cursor-row vd)))
		 (incf (vd-cursor-column vd)))))


That's just an example of the sort of thing one can do, and none of the
particular operations should be taken as suggestions for how a virtual display
should work.

Yes, it's more verbose than flavors, but it is portable and perhaps more
efficient than a flavor-based system would be.  Such a system CAN be extended
by the user.  Do you still think we'd be too constrained by implementing a
virtual display system with structures?


∂19-Nov-84  2220	FAHLMAN@CMU-CS-C.ARPA 	Proposals and questions    
Received: from CMU-CS-C.ARPA by SU-AI.ARPA with TCP; 19 Nov 84  22:17:38 PST
Received: ID <FAHLMAN@CMU-CS-C.ARPA>; Tue 20 Nov 84 01:16:25-EST
Date: Tue, 20 Nov 1984  01:16 EST
Message-ID: <FAHLMAN.12064983964.BABYL@CMU-CS-C.ARPA>
From: "Scott E. Fahlman" <Fahlman@CMU-CS-C.ARPA>
To:   Cl-Windows@SU-AI.ARPA
Subject: Proposals and questions
In-reply-to: Msg of 19 Nov 1984  23:33-EST from Skef Wholey <Wholey>

I agree with much of what Skef Wholey says -- especially the part about
being able to find out which class of display device you have -- but I
don't think I agree that "any virtual display should support all
operations".  The problem is that there are some things you want to do
on a bitmap that just have no counterpart on a 24x80 ASCII terminal
(smart or not).  If we throw all of these things out, we get an interface
for bit-mapped displays that is less powerful than it should be, which
means that more users will write their code using non-standard calls to
get at the display's real power.

Probably the right move is to make the operations for the feeble
displays a subset of those available on the more powerful ones.  In some
cases, we might want the operations for more powerful displays to
recognize additional keywords (such as :COLOR).  We should try to keep
the number of distinct levels fairly small, however.

On the issue of whether to use objects, I think that we cannot define an
object-orineted interface until the Common Lisp community settles on
some particular object-oriented system as being required on all
implementations (though other object systems might co-exist with this).
I don't expect to see this any time soon -- if a standard is to emerge
at all, it will only be AFTER people have had a chance to play with
portable Flavors and Loops and assorted other things and decide what
they like.  I think that we can define a reasonable set of
somewhat-extensible interfaces in a portable non-flavorish way; if we
have to sacrifice some extensibility, that's better than having no
common window interface at all.

-- Scott

∂20-Nov-84  0736	boetje@DEC-HUDSON 	documenting implementations    
Received: from DEC-HUDSON.ARPA by SU-AI.ARPA with TCP; 20 Nov 84  07:35:44 PST
Date: Tue, 20 Nov 84 10:36:01 EST
From: boetje@DEC-HUDSON
Subject: documenting implementations

I think the discussion of structures vs object implementation is getting a
little off track. The issues (it seems to me) revolve around the form of the
creation, accessing and setting functions for virtual displays and the method
by which the user can extend the functionality of the virtual display system
Let me address some high level considerations of each issue.

When I say that I prefer a structure implementation for the CL standard, I'm 
not saying that I intend that the DEFSTRUCT for various things be defined in 
the standard. My intention is that we document and standardize creation, 
accessing and setting functions that look like

	(setq display-1 (make-virtual-display ...))
	(virtual-display-label display-1)
	(setf (virtual-display-label display-1) ...)

as opposed to instancing of objects and sending messages to the instances. I 
think that under no circumstances should we document a particular DEFSTRUCT 
implementation and require all Common LISPs to have this. I think that the 
only reason to do this (and it's part of the example Skef gives) is to allow 
users to support output devices not explicitly supported by the vendor. This 
will get us rapidly down a rat hole of terminal support issues. Support of 
"non-vendor" terminals should be an issue for the vendor to address in 
whatever way is most efficient on his system. On the other hand, functions 
such as SET-CURSOR-POSITION should exist in all the CL implementations and do 
the right thing on all supported terminals. If the vendor provides an 
implementation dependent way to define support for other terminals, then the 
positioning function will do the right thing on these other terminals as well. 

Extending the capabilities of operations on virtual displays is a real issue. 
On the other hand, it's not clear that we have to address this right now. I 
propose that we investigate defining a fairly "complete" range of 
functionality which assumes the availability of a nice (color, bitmapped) 
display and then look at subsetting this functionality to cell-oriented 
terminals. A part of this may be defining a number of inquiry functions which 
let the program tailor itself to the capabilities of the run-time device. This 
means that we're likely to end up in the same place as the GKS standard which 
has more inquiry functions than all the other kinds of function combined. 

We can probably have some high level inquiry functions that let the user know
the general category of device (bitmapped, color, vector, cell, etc). Each
category would have a certain level of functionality that's required (by the
standard) for that device and a certain set that's optional and up to the
implementation (eg, narrow virtual displays on a VT100).

∂20-Nov-84  0850	WHOLEY@CMU-CS-C.ARPA 	Virtual Displays  
Received: from CMU-CS-C.ARPA by SU-AI.ARPA with TCP; 20 Nov 84  08:49:57 PST
Received: ID <WHOLEY@CMU-CS-C.ARPA>; Tue 20 Nov 84 11:48:43-EST
Date: Tue, 20 Nov 1984  11:48 EST
Message-ID: <WHOLEY.12065099060.BABYL@CMU-CS-C.ARPA>
From: Skef Wholey <Wholey@CMU-CS-C.ARPA>
To:   CL-Windows@SU-AI.ARPA
Subject: Virtual Displays

    From: Scott E. Fahlman <Fahlman>

    I don't think I agree that "any virtual display should support all
    operations".  The problem is that there are some things you want to do
    on a bitmap that just have no counterpart on a 24x80 ASCII terminal
    (smart or not).  If we throw all of these things out, we get an interface
    for bit-mapped displays that is less powerful than it should be, which
    means that more users will write their code using non-standard calls to
    get at the display's real power.

I believe that the sorts of things you're talking about are in the domain of
CL-Graphics.  I could be wrong.  Could you give me an example of such
operations?  I have a feeling that either they should be hidden by something
very high level (e.g. HALFTONE-RECTANGLE could really halftone a portion of a
raster display, but put a portion of a Concept-100's screen into half-bright
mode), or that they can be implemented by mashing vanilla CRT's into 24x80
raster displays using 1x1 fonts (MOVE-RECTANGLE could do a BITBLT on a raster
display, but actually copy stuff around on other terminals (actually, for dumb
termiansl this would require the VD system to maintain a screen image, which
may or may not be a good idea (but Concept-LNZ's DO have such an operation))).

Perhaps we need to decide on operations before we determine if there needs to
be the distinction that Scott suggests there ought to be.  I think a virtual
display should try its best to perform an operation, but quietly ignore the
request if it can't hack it.  It could bum someone out if a nifty piece of
software didn't run on her computer just because she had a dumb terminal.  If
instead, the display just didn't look as nifty on an ADM-3A as it does on a
Lisp Machine, then the user will probably be forgiving.

    From: boetje at DEC-HUDSON

    I think the discussion of structures vs object implementation is getting a
    little off track.

I was attempting to show that the niceness of an object-oriented approach could
still be had within the Common Lisp language, and with structures.  Perhaps I
should have said "Object oriented programming is a style, and one can write
stylized Common Lisp," and left out all the code in my last message.

    My intention is that we document and standardize creation, accessing and
    setting functions that look like
    as opposed to instancing of objects and sending messages to the instances.

Sure.  Note that the Display-Char function (intended to be the user-level call)
in my example hid the object oriented implementation.  Streams are the done the
same way, for us.

    I think that under no circumstances should we document a particular
    DEFSTRUCT implementation and require all Common LISPs to have this. I think
    that the only reason to do this (and it's part of the example Skef gives)
    is to allow users to support output devices not explicitly supported by the

So we're just working on a spec here, and not a portable implementation.  Ok.
I think a portable implementation or two will come out of this, though.  The
people doing those implementations probably want to think hard about
extensibility for the sake of porting to new environments in addition to
supporting new devices.

    We can probably have some high level inquiry functions that let the user
    know the general category of device (bitmapped, color, vector, cell, etc).
    Each category would have a certain level of functionality that's required
    (by the standard) for that device and a certain set that's optional and up
    to the implementation (eg, narrow virtual displays on a VT100).

I have a feeling that trying to do things in explicit levels is going to let
capabilities of some terminals fall through the cracks.  I claim that the
problem Scott brought up in the first paragraph quoted above can work in
reverse -- some character-oriented CRT's can do operations like
raster-oritented displays, and others can do different ones.  Maybe this isn't
a problem, but we can't tell for sure until we get into specifics.  Anyone up
for that?


∂21-Nov-84  0724	FAHLMAN@CMU-CS-C.ARPA 	Virtual Displays 
Received: from CMU-CS-C.ARPA by SU-AI.ARPA with TCP; 21 Nov 84  07:23:14 PST
Received: ID <FAHLMAN@CMU-CS-C.ARPA>; Wed 21 Nov 84 10:22:01-EST
Date: Wed, 21 Nov 1984  10:21 EST
Message-ID: <FAHLMAN.12065345435.BABYL@CMU-CS-C.ARPA>
From: "Scott E. Fahlman" <Fahlman@CMU-CS-C.ARPA>
To:   Skef Wholey <Wholey@CMU-CS-C.ARPA>
Cc:   CL-Windows@SU-AI.ARPA
Subject: Virtual Displays
In-reply-to: Msg of 20 Nov 1984  11:48-EST from Skef Wholey <Wholey>

I'm not sure if my view of the dividing line between CL-WINDOWS and
CL-GRAPHICS matches other people's.  I had been assuming that such
things as the primitive calls to display characters in a window at
arbitrary places, draw lines, color in rectangles, and so on were the
provine of the window package, and that any graphics standard is more
concerned with higher-level software to help decide which lines to draw
where.  (If graphic means anything that is written into a virtual
display at all, then we have to consider graphics and windows together
because at that level they are inseparable.)

If my view of the division is correct, then there are several examples
of things that a raster-scan display could do that would have no
immediate counterpart on a dumb terminal: draw lines from one point to
another, display an arbitrary character from an arbitrary font at a
specific location specified in pixels, rotate a chunk of the screen,
return a mouse-click (or some other kind of pointer-selection) in window
coordinates, etc.

I think that it is a terrible mistake to rule out any of these
operations for raster displays just because there is no good equivalent
on an 24x80 character terminal.  I also think that it is not in general
possible to have the built-in window-based software fake all of these
things in "the best way possible" on the dumb terminal.  There's just no
good way to fake a drawing program on an Adm-3A, and I'd rather have the
software fail cleanly than waste a lot of time trying.  Maybe a clever
application programmer can figure out some way to fake his particular
drawing program on a dumb terminal, using the impoverished set of
operations available there, but that should be his problem and not the
Lisp implementor's problem.

So, revised proposal:

We divide features that a diplay might have into broad classes that tend
to go together: Multiple windows, Advanced cursor commands, Pixel
operations, Pointing device, Color, Multiple Fonts, etc.  Some of these
have parameters, such as the X and Y dimensions of the screen in
characters or pixels.  Each display/implemenation is required to
indicate which of these things it has and the values of its parameters,
and therefore what operations it supports.  Software will be written to
assume some set of these feature groups, and the necessary support will
be advertised with the documentation for the software.  If I want my
package to run on ANYTHING, I assume a very minimal set of support; if I
don't want to live with those restrictions, then I assume more.  The
best software providers will conditionalize their code so that if some
feature like color is present, it is used, but if it is not present they
compensate for this in some other way; others may choose not to bother
trying to cope with dumb displays.

-- Scott

∂21-Nov-84  0914	DDYER@USC-ISIB.ARPA 	Implementation strategy 
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 21 Nov 84  09:14:26 PST
Date: 21 Nov 1984 09:13:20 PST
Subject: Implementation strategy
From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
To: cl-windows@SU-AI.ARPA

Now that I've lighted the fire, I'll add my contribution to the fuel.

We have to define virtual display operations in a way that is acceptable
to the major implementations, or else the definition will simply be
rejected as brain damaged and ignored.  In particular, it should be
obvious that Symbolics isn't going to re-implement their window system
using structures.  It's just as obvious, as was pointed out, none
of the other CL implementations will have a robust and portable object
oriented system for an indeterminate time.   Therefore, we must define
something compatible with either strategy, and preferably, one that
will permit the underlying implementation to change, as object
systems become available.

What this amounts to is defining a limited object oriented system,
which maximizes information hiding but makes no commitment about
implementation.  The last time I implemented such a system, my
basic primitives looked like this.

(SCREENOP <<window>> <<operation>> &rest args)

Honest Injun, I came up with it before I ever wrote my first DEFFLAVOR!

This was implemented by a hairy macro, which expanded to structure
manipulations appropriate to the operation.  To hack efficiency,
one "operation" was :GET-HANDLER-FOR and another was :INVOKE-HANDLER-FOR.
We might also want an environment macro like 
Where WINDOW would be decoded (whatever that means) so that references
to VAR would know the exact type of the operand.  

The advantages of this approach are that it is easy to transform
into efficient code for most any implementation, it avoids embedding
implementation details in user code, it makes screen manipulations
easily identifiable, and it avoids polluting the global environment
with arbitrarily many names of operations.   I strongly favor this
kind of surface structure for invoking display operations.

The problem of creating an abstract syntax for defining window types
is stickier.


∂21-Nov-84  1048	KACZMAREK@USC-ISIF.ARPA 	Re: Virtual Displays
Received: from USC-ISIF.ARPA by SU-AI.ARPA with TCP; 21 Nov 84  10:48:12 PST
Date: 21 Nov 1984 10:45:02 PST
Subject: Re: Virtual Displays
To: "Scott E. Fahlman" <Fahlman@CMU-CS-C.ARPA>
cc: cl-windows@SU-AI.ARPA
In-Reply-To: <FAHLMAN.12065345435.BABYL@CMU-CS-C.ARPA>

Typical graphic standards provide a great deal of functionality regarding
the display of lines, circles, points, raster images, and characters.  They
also provide for clipping regions, rotation of images, panning, zooming, and
scaling.  I think that a window package should be built on top of graphic
support.  We should assume the existence of font support (including producing 
bitmaps for text strings), clipping, line drawing, shading, texturing,
coloration, etc..  We should also presume high level primitives for
pointing devices ala GKS and the Siggraph Core standard.

I suggested this in an earlier message but no one seemed to pick up on it
other than to say they wanted to do all the low-level stuff.  I would like
to get a measure on how many people think that windows are at a higher
level than graphics.  I see windows as graphic structures with fairly
restrictive constraints--they are a major component of the user interface
with highly stylized behavior.  They have to be flexible enough to allow an
application programmer to mold the user interface to his liking, yet
restrictive enough so that the user is not overwhelmed by inconsistencies.
I think we ought to check with the graphics group also to get their
feelings to make sure we are not duplicating efforts.


∂21-Nov-84  1250	greek@DEC-HUDSON 	Terminal features and graphic functions   
Received: from DEC-HUDSON.ARPA by SU-AI.ARPA with TCP; 21 Nov 84  12:49:51 PST
Date: Wed, 21 Nov 84 15:50:10 EST
From: greek@DEC-HUDSON
Subject: Terminal features and graphic functions
To: cl-windows@su-ai

I basically agree with what Scott says about categories of features.
Perhaps we might even end up with some standard symbols in *FEATURES*
for testing by programs.  However, I'm dubious as to the patience
of developers as they try to write code that uses as many features
as possible but avoids ones not on the current terminal.  This kind
of code is difficult to write, and people just tend to write
for the lowest common denominator, or say "screw" to all but the
smartest terminals.

I think we can define virtual displays that will work pretty well
on many kinds of terminals.  If we said that all, or almost all,
operations had to work on all terminals, and forced implementors
to think of ways to do these on dumb terminals (or noop them), we
would be doing the world a favor.  As for complex graphics, that
have no counterpart on dumb terminals, perhaps we shouldn't be
treading on that ground.  Graphics is not a solved problem.

Dave - I don't understand why your statements about window 
compatibility with existing implementations leads you to believe
that the operations must be object-oriented.  What's wrong with
50 functions?  If Symbolics implements these as macros that turn
into flavorful things, no problem.  Streams are object-oriented,
structures aren't, hash tables aren't, arrays aren't.  Why start
now, when we haven't agreed on object-oriented features for CL?
(Read that as "streams aren't object...").

- Paul

∂21-Nov-84  1434	@MIT-MC:MONTALVO@MIT-OZ 	Re: Virtual Displays
Received: from MIT-MC.ARPA by SU-AI.ARPA with TCP; 21 Nov 84  14:34:23 PST
Date: Wed 21 Nov 84 17:31:34-EST
From: Fanya S. Montalvo <MONTALVO%MIT-OZ@MIT-MC.ARPA>
Subject: Re: Virtual Displays
In-Reply-To: Message from "Tom Kaczmarek <KACZMAREK@USC-ISIF.ARPA>" of Wed 21 Nov 84 10:45:02-EST

I think a lot of the issues being raised by cl-windows are relevant to
cl-graphics, and that the relationship between windows and graphics
should be discussed by cl-graphics, also.

I see windows as a subset of graphics.  Support for windows is a
specific kind of functionality that a graphics package may or may not
have.  As a subset, it's neither higher nor lower than graphics.  It
may rely on low-level primitives, but in turn, some even higher level
functionality may rely on it.

And by the way, I'm on cl-graphics also, and may have missed the
discussion of how the division was being made.  If it was already
discussed just forward the relevant messages (not too many please).


∂26-Nov-84  0717	boetje@DEC-HUDSON 	graphics, virtual displays, and terminals
Received: from DEC-HUDSON.ARPA by SU-AI.ARPA with TCP; 26 Nov 84  07:16:27 PST
Date: Mon, 26 Nov 84 10:13:21 EST
From: boetje@DEC-HUDSON
Subject: graphics, virtual displays, and terminals

On categories of features, here's one suggestion for a basic division...

Take some dumb terminals of the VT100 class. These have the ability to
position a cursor to an arbitrary cell location and write ASCII characters
This is sufficient capability support virtual displays which can have a border
and a label. The set of operations has to be restricted to manipulating text
on a cell-oriented terminal (ie, no proportional fonts). There is a suprising
amount that can be implemented on such a terminal: show arbitrary sized
displays, insert and delete characters (easier on a cell terminal), scroll
lines of text in a display, occlude displays, pick and point via cursor
manipulation and even draw horizontal and vertical lines. For a dumb terminal,
that ain't bad.

The other category then becomes the bitmapped tubes. Let's just assume they 
can do whatever we think up (although character insertion and deletion is 
harder on these terminals). It's up to us to establish a reasonable set of 
operations that should be supported.

So I'd choose two categories: the kitchen sink and the text only. The text 
only terminal is required to be cell-oriented and have the capability to 
position the terminal cursor at an arbitrary cell position. It can support all 
the capabilities needed for a screen editor. The kitchen sink terminal is 
bitmapped and can support an arbitrary level of complexity in its display 

On the division of virtual displays and graphics...

The more I've thought about it, they really are fairly separate topics which 
have one area of overlap. Each topic has a number of basic operations and 
concepts which don't relate at all to the other. For example, a discussion of 
virtual displays gets into issues of display management which includes ideas 
such as stacking, occlusion and selection. Graphics deals a lot with 
coordinate transformation, line drawing, graphical objects and area fill. 

The one area of overlap can be neatly defined if we define the picture area of 
a virtual display to be that portion of a display inside of things like labels, 
borders and margins. The picture area is where most everything of interest 
happens in a virtual display. The picture area is also allowed to be a 
graphics viewport onto some data space (such as NDC for you GKS fans). If we 
accept this definition, then the tasks of the display committee and the 
graphics committee become a bit easier. We need to refine things such as the 
coordinate system of the virtual display. Once this is done, the graphics 
committee can concern itself with coordinate transformations, composition, 
basic operations and picking. The display committee can be concerned with 
management of virtual displays, use of a virtual display in place of a CL 
stream, and the definition of what surrounds a virtual display (labels, 
borders, margins, etc).


∂08-Dec-84  1642	DDYER@USC-ISIB.ARPA 	Easy Questions
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 8 Dec 84  16:42:42 PST
Date:  8 Dec 1984 16:41:41 PST
Subject: Easy Questions
From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
To: cl-windows@SU-AI.ARPA

I'd like to gauge the "real world" concerns of the members of this
list regarding portable windows.   Feel free to editorialize.  The
questions are:

	What existing, under development, or planned programs
	would use common lisp's window system if it had one?

	What existing, under development, or planned programs
	would NOT use common lisp's window system, even if
	it had one?  Why?

∂08-Dec-84  1927	FAHLMAN@CMU-CS-C.ARPA 	Easy Questions   
Received: from CMU-CS-C.ARPA by SU-AI.ARPA with TCP; 8 Dec 84  19:27:18 PST
Received: ID <FAHLMAN@CMU-CS-C.ARPA>; Sat 8 Dec 84 22:27:55-EST
Date: Sat, 8 Dec 1984  22:27 EST
Message-ID: <FAHLMAN.12069934029.BABYL@CMU-CS-C.ARPA>
From: "Scott E. Fahlman" <Fahlman@CMU-CS-C.ARPA>
Cc:   cl-windows@SU-AI.ARPA
Subject: Easy Questions
In-reply-to: Msg of 8 Dec 1984  19:41-EST from Dave Dyer <DDYER at USC-ISIB.ARPA>

This question is not so easy.  The answer depends totally on what the
standard Common Lisp window system ends up looking like.  In the Spice
Lisp system (on the Perq, at present) we now have a simple set of Lisp
function calls that gives us efficient access to the window and graphics
operations available in the system: window creation and deletion, what
appears in the title line and progress bar, what appears in the icon
associated with the window, line drawing, character moves, raster ops,
reading from the screen bitmap, and so on.  Actually, all of these
services are provided outside of the Lisp process, and the calls turn
into messages to the system kernel or to the screen-manager process, but
the user doesn't need to know that.

If the window/graphics standard turns out to be a set of function calls
that gives us access to all of the same kinds of operations, then we
would probably use it for most of our graphics-oriented applications and
possibly even for the Hemlock editor.  This would become the standard
set of screen-oriented function calls in our Lisp system.

If the standard provides access only to a small subset of the Spice
display facilities, or enforces a substantially different view of the
display abstractions than our system supports, or if it is grossly
inefficient for some reason, then we would probably use the native Spice
calls for all of our local programming, but would occasionally translate
certain vanilla applications or utilities into the Common Lisp
graphics/window standard for export.

If, in the interest of extensibility or whatever, the standard window
system ends up being object-oriented and ultra-hairy like the current
Zetalisp window system, I don't think it will be used at all at CMU,
except by the one or two people who have been writing graphics code on
our Lisp machines and have somehow manged to figure this stuff out.

-- Scott

∂11-Dec-84  1207	DDYER@USC-ISIB.ARPA 	Re: Easy questions 
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 11 Dec 84  12:07:22 PST
Date: 11 Dec 1984 12:02:13 PST
Subject: Re: Easy questions
From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
To: cl-windows@SU-AI.ARPA

Replies from: 
            8-Dec Kent M Pitman        easy questions? (1327)
            8-Dec John W. Peterson     Re: Easy Questions (3632)


Date: 8 December 1984 19:54-EST
From: Kent M Pitman <KMP @ MIT-MC>
Subject: easy questions?

Actually, the second question is quite hard. It's easy to say
"Oh, yeah, if you provided me a window system, I'd use it for ..."
without knowing what it offered because it's a "friendly" thing to
say and people will be willing to suppose your window system will
"meet their needs". Saying I wouldn't use a window system even
if you gave it to me is to say you don't believe it would meet your
needs no matter what, which either says you strongly believe that 
there are two different viable theories of window systems and that
you want one but believe CL will provide the other, or that you 
believe there's only one such system and CL doesn't stand a chance
in hell of going the right direction.

Anyway, it occurs to me that you might ammend the second question, or
add a third, to find out what features that if a window system lacked
would make it useless, or what features that if a window system had
would make it useless. eg, you might have said:
  "What kind of window system would not suit some existing, under
   development, or planned program?"


Date: Sat 8 Dec 84 18:25:06-MST
From: John W. Peterson <JW-Peterson@UTAH-20.ARPA>
Subject: Re: Easy Questions

        What existing, under development, or planned programs
        would use common lisp's window system if it had one?

I'm currently working on a CAGD (Computer Aided Geometric Design) system under
lisp.  It is extensivly window based, and designed to be portable to some
degree (versions currently run on devices such as Apollo domains and Evans &
Sutherland PS300 Vector engins).  The system is "different" from most CAD
environments in that a program (a "procedural model") is written to describe
the part you are constructing.  These programs "emit" B-Spline surfaces, which
are then used to generate shaded images, N/C toolpaths, etc.  We use 
interactive (3-Dimensional) graphics to view the model as it is constructed.
This is coupled with a special version of SETF that displays the graphics
representation of an entity (point, line, arc, curve, surface, etc) in a
graphics window when it's value is assigned.  Multiple graphics windows can
be used to view differnt (or different views of the same) geometric 
constructions.  At any time you can grab a knob and rotate the geometry in
a 3D window to get a better view (this happens in real time on the E&S tubes,
step-by-step on less powerful displays).

Since the model is built from a lisp program, a text editor (usually a full-
featured EMACS) window is used to write the program in.  You evaluate your
program step-by-step in the emacs window; and see the geometric results in
the graphics window as you go along.  

A current (and very tricky!) research issue is to be able to interactivly
modify the graphics representation of the model (in the graphics window) and
have these changes reflected in your program.  Thus, the textual representation
of the model in your EMACS window would get automaticly updated, much like
the graphics is updated now when you change the text.  [A master's student
here has done some preliminary work with this].

Currently this is all done with, well, a lot of masking tape.  We have a
PSL (Portable Standard Lisp) process running under the control of Gosling's
emacs.  The PSL process in turn drives the several graphics windows, updating
them whenever a SETF occurs on a geometric object.  In my ideal universe,
this would be running as a single Lisp program on a powerful Lisp Machine.
But these weren't readily available to us when we started (80-81), and
many of our contractors would still balk at an $80K/User workstation.

Hmmm, that's probably a longer discription than you bargianed for, but I guess
it's a useful example of a -complex- application for a Lisp-based window 
system.  After all, I want these windows to do everything from powerful
text editing to real-time 3D graphics...

I would find a summary of the applications you here about interesting.  And
as to your other question:
        What existing, under development, or planned programs
        would NOT use common lisp's window system, even if
        it had one?  Why?

About the only code I can think of that falls into this catagory are 
ones that aren't interactive (i.e, rendering programs that take a long time
to run).  But even then, I STILL want those windows for debugging and editing

∂12-Dec-84  2201	RAM@CMU-CS-C.ARPA 	Easy Questions  
Received: from CMU-CS-C.ARPA by SU-AI.ARPA with TCP; 12 Dec 84  22:01:46 PST
Received: ID <RAM@CMU-CS-C.ARPA>; Thu 13 Dec 84 01:02:24-EST
Date: Thu, 13 Dec 1984  01:02 EST
Message-ID: <RAM.12071010731.BABYL@CMU-CS-C.ARPA>
From: Rob MacLachlan <RAM@CMU-CS-C.ARPA>
Cc:   cl-windows@SU-AI.ARPA
Subject: Easy Questions

    I have a suspicion that the Hemlock text editor will not use any
window standard which may be agreed upon.  Hemlock is currently in use
in the CMU community, and a much mutilated early version forms the
basis of the DEC VAX Lisp editor.  It is about 20k lines of largely
portable Common Lisp code.  The current Hemlock screen manager is
inadequate, and one of my current projects is to design a new one.
The main functions of the screen manager will be the following:
 1] Allocate windows in a manner culturally compatible with EMACS.
 2] Provide primitives for drawing strings and copying and clearing
    screen areas.
 3] Provide some sort of abstract interface to multiple fonts of
    varying heights and widths.  I have something in mind along the
    lines of Scribe font-families.
 4] Deal with demultiplexing keyboard and mouse input.
 5] Provide some sort of abstract interface to the software interrupts
    generated by our window system when windows are exposed or
 6] Have some sort of support for highlighting.

    Some reasons I don't think that a portable window manager is likely to be
 A] Some of things that need low-level support in the window system
    (4, 5) probably cannot be resolved to everyone's satisfaction.
 B] Efficiency is important, thus it may be desirable to add special
    primitives to make the drawing primities provided more closely
    correspond to those actually supported.

Other comments:

    I am not very impressed by environment query functions, or rather
the programming style they seem to encourage.  Redisplay, which is the
level above the screen manger, needs to have a very good idea of what
the device can and cannot do.  What I intend to do is have several
different versions of redisplay which are selected on the basis of the
general class of device driven, e.g. bit-mapped screen, windowing
terminal, smart terminal, dumb terminal.  If it is necessary to have
significant procedural knowledge about the device at a level above the
window system to attain good performance across a wide range of
devices, it is futile for the window system to attempt to hide the
fundamental characteristics of the device.

    If graphics includes such things as scaling, symbols, rotation and
arbitrary coordinate transforms, then I think that it is wrong to
think of "Windows" as being a layer above "Graphics".  It is true that
any window system will be based on some set of graphical primitives
for doing things such as rasterop and drawing lines, but these things
will operate in device units, and thus will not be the primitives of
the graphics system.  I suspect that it is much more probable that the
graphics system be built on the window system, since graphics will
probably be done on the windows or "virtual displays" provided by the
window system, while the window system will have no use for any of the
hair provided by the graphics package.


∂09-Jan-85  0110	DDYER@USC-ISIB.ARPA 	This space intentionally left blank    
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 9 Jan 85  01:10:32 PST
Date:  9 Jan 1985 01:07:31 PST
Subject: This space intentionally left blank
From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
To: cl-windows@SU-AI.ARPA

 I've been impressed by both the high quality and the low volume
of discussion on this mailing list.  I think this is indicative
of an unfortunate state of affairs.  We collectively appreciate 
the nuaces of and appreciate the magnitude of "the window problem",
hence the high quality.  We collectively agree on most issues of
substance, hence the low volume.

 This would be fine, except there is no CL window system, and
at this rate, there never will be!   Why this paralysis?  I suspect
we also share the resigned realization that a combination of
vested interests and inertia will defeat any effort to establish
a standard.


∂09-Jan-85  1001	KACZMAREK@USC-ISIF.ARPA 	Dire Dyer Prediction
Received: from USC-ISIF.ARPA by SU-AI.ARPA with TCP; 9 Jan 85  10:01:43 PST
Date:  9 Jan 1985 08:02:54 PST
Subject: Dire Dyer Prediction
To: cl-windows@SU-AI.ARPA
In-Reply-To: (Message from "Dave Dyer <DDYER@USC-ISIB.ARPA>" of 9 Jan 1985 01:07:31 PST)

I think that the dire Dyer prediction is premature.

I take the volume of messages for this group as a positive sign.  It has
been considerably higher for this group than for the two other groups I
know about.  The volume of messages has reduced lately indicating, as Dave
points out, agreement on the issues.  (Should the volume be seasonally
adjusted?  We have all probably had more vacation days/holidays recently
than normal.)  I think any drop in volume indicates that we are at a
critical point--we are ready to start the process of design.  I would
suggest that we need someone, preferably who already has a design for a
window system, to step forward and propose it as the standard.  (If more
than one volunteer steps forward we ought to consider multiple proposals.)
Published proposals followed by a several day workshop to discuss them
seems appropriate to me.

The proposals are sure to cause controversy and vested interests are
certainly going to play a part in the negotiations that follow.  Some
groups will decide not to follow the standard and others will.  That is
nothing new.  I don't think we ought to admit defeat just yet.



∂09-Jan-85  1117	DDYER@USC-ISIB.ARPA 	Re: This space intentionally left blank
Received: from USC-ISIB.ARPA by SU-AI.ARPA with TCP; 9 Jan 85  11:17:08 PST
Received: FROM UTAH-20.ARPA BY USC-ISIB.ARPA WITH TCP ; 9 Jan 85 01:33:45 PST
Date: Wed 9 Jan 85 02:35:55-MST
From: John W. Peterson <JW-Peterson@UTAH-20.ARPA>
Subject: Re: This space intentionally left blank
cc: JW-Peterson@UTAH-20.ARPA
In-Reply-To: Message from "Dave Dyer       <DDYER@USC-ISIB.ARPA>" of Wed 9 Jan 85 01:07:31-MST
ReSent-Date:  9 Jan 1985 11:16:59 PST
ReSent-From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
ReSent-To: cl-windows@SU-AI.ARPA, cl-graphics@SU-AI.ARPA

A related question.  I thought (or at least was under the impression) that
I was tuned into the CL-GRAPHICS list as well.  I have not heard a *peep* out
of that list, do you know if it's active?

This is somewhat relavent to CL-Windows, since I am from the school of thought
that the window system should know about (and perhaps be based on) the
graphics support.  To some extent, I've been "waiting" to see what that list
says  (This may hold true for others as well, e.g., the "units of measurement"
discussion a while back).


∂09-Jan-85  1322	boetje@DEC-HUDSON 	here's something to make up for the long silence... Jerry    
Received: from DEC-HUDSON.ARPA by SU-AI.ARPA with TCP; 9 Jan 85  12:59:45 PST
Date: Wed, 09 Jan 85 15:10:33 EST
From: boetje@DEC-HUDSON
Subject: here's something to make up for the long silence... Jerry

                                                        9 January 1985

                             COMMON LISP

                           Graphics Models
                                                               Page ii


        1       INTRODUCTION . . . . . . . . . . . . . . . . . . . . 1
        1.1       Purpose  . . . . . . . . . . . . . . . . . . . . . 1
        1.2       Terms  . . . . . . . . . . . . . . . . . . . . . . 1
        2       GENERAL CONCEPTS . . . . . . . . . . . . . . . . . . 2
        3       COORDINATE SYSTEMS . . . . . . . . . . . . . . . . . 4
        3.1       Application, World, User Coordinates . . . . . . . 5
        3.2       Master, Object Coordinates . . . . . . . . . . . . 5
        3.3       Physical Device Coordinates  . . . . . . . . . . . 5
        3.4       Logical Device Coordinates . . . . . . . . . . . . 6
        3.5       Virtual Display Coordinates  . . . . . . . . . . . 6
        3.6       Normalized Device Coordinates (NDC)  . . . . . . . 7
        4       TRANSFORMATION . . . . . . . . . . . . . . . . . . . 8
        4.1       Rotation . . . . . . . . . . . . . . . . . . . . . 8
        4.2       Scaling  . . . . . . . . . . . . . . . . . . . . . 8
        4.3       Translation  . . . . . . . . . . . . . . . . . . . 8
        5       TRANSFORMATION OPERATIONS  . . . . . . . . . . . . . 9
        5.1       Matrix Representation  . . . . . . . . . . . . . . 9
        5.2       Window-Viewport Transformation . . . . . . . . . . 9
        5.3       Active Transformation  . . . . . . . . . . . . .  10
        6       CLIPPING RECTANGLE . . . . . . . . . . . . . . . .  10
        7       COMPOSITION  . . . . . . . . . . . . . . . . . . .  11
        7.1       Composition Space  . . . . . . . . . . . . . . .  11
        7.2       Segments . . . . . . . . . . . . . . . . . . . .  12
        7.3       Virtual Display Composition  . . . . . . . . . .  12
        7.4       COMMON LISP Composition Levels . . . . . . . . .  13
        8       ATTRIBUTES . . . . . . . . . . . . . . . . . . . .  13
        8.1       Attribute Descriptions . . . . . . . . . . . . .  13
        8.2       Attribute Inheritance  . . . . . . . . . . . . .  16
        9       VIRTUAL DISPLAYS . . . . . . . . . . . . . . . . .  17
        9.1       Composition Space  . . . . . . . . . . . . . . .  18
        9.2       Picture Area . . . . . . . . . . . . . . . . . .  18
        9.3       Banner Area  . . . . . . . . . . . . . . . . . .  18
        9.4       Border . . . . . . . . . . . . . . . . . . . . .  19
        9.5       Margin . . . . . . . . . . . . . . . . . . . . .  19
        9.6       Virtual Display Window . . . . . . . . . . . . .  19
        9.7       Device Viewport  . . . . . . . . . . . . . . . .  19
        9.8       LISP Terminal Streams To Virtual Devices . . . .  19
        9.9       Input Cursor . . . . . . . . . . . . . . . . . .  20
        10      POINTING AND PICKING . . . . . . . . . . . . . . .  20
        10.1      Pointing   . . . . . . . . . . . . . . . . . . .  21
        10.2      Picking  . . . . . . . . . . . . . . . . . . . .  21
        11      DISPLAY MANAGEMENT . . . . . . . . . . . . . . . .  21
        11.1      Visibility And Stacking  . . . . . . . . . . . .  22
        11.2      Sensitive Regions  . . . . . . . . . . . . . . .  23
        11.3      Menus  . . . . . . . . . . . . . . . . . . . . .  23
        11.4      Pointer And Selection  . . . . . . . . . . . . .  23
        12      BITMAPS  . . . . . . . . . . . . . . . . . . . . .  24
COMMON LISP Graphics Models                                     Page 1


1.1  Purpose

This somewhat ambitious document is an attempt to establish  a  common
framework  for discussions of graphics, windows, virtual displays, and
all the supporting concepts that go along with them.  It  specifically
doesn't define LISP functions yet.  My claim is that without agreement
at the level of concepts and terminology, we can't possbly get started
on defining LISP functions.

The material presented here covers concepts and terms  which  properly
belong  to  both  the graphics and windows committees.  The reason for
this is to present a unified view  toward  video  displays  before  we
define  functions.   I  believe that when we start defining functions,
we'll find a fairly neat partition of functions between  graphics  and
virtual  display  creation  and  management.  But we're less likely to
have functional incompatibilities if we can agree on some  high  level

A section missing from this document is  a  discussion  of  levels  of
capabilities  that  can  be supported by various hardware and software
implementations.  I'd welcome ideas on this.  As  a  first  cut,  I'll
propose three levels:

     1.  That which you can do on a cell-oriented  character  terminal
         such  as a VT100 (text editor capabilities, multiple displays
         and simple menus).

     2.  Add basic graphics operations but without composition.  Level
         2  might  include  restricted composition of virtual displays
         (no additional scaling or rotation) much like the  frame/pane
         systems around.

     3.  Full multi-level composition  capability  and  allowance  for
         user-written N-dimensional processing.

With some luck, this should start a new flood  of  discussion.   Happy

1.2  Terms

Terms will be defined in this document by  establishing  the  concepts
they  represent.   This  will not only provide context and explanation
but show the functional interrelationships among  the  various  terms.
Where  possible,  "established" terms will be used.  A difficulty with
the  current  industry  environment  is  that  the  same  word   (e.g.
"window")  is  often  used to represent very different concepts.  Such
industry discrepancies will be noted.

At least the following terms will be defined:
COMMON LISP Graphics Models                                     Page 2

     Clipping rectangle
     Display management
     Virtual display

The presentation of conceptual  models  is  designed  to  explain  and
illustrate  both the generalization of certain techniques, such as the
window-viewport transformation, and the methods by which  COMMON  LISP
integrates  the  various  objects  and  operations  that  support  the


This paper deals with the concepts used in displaying data on a  video
terminal.   Such  a  display might be as simple as placing consecutive
lines of text on a screen.   It  might  also  involve  drawing  lines,
shading  figures,  and overlapping independent displays.  This process
can be made arbitrarily complex.  Certain conventions  and  techniques
have  evolved  for defining and managing this process.  Unfortunately,
different conventions and terminology have evolved  in  the  different
worlds  of  display  management  and  graphics.   Much  of  this paper
describes a system of terminology and concepts which attempts to unify
the different approaches taken by display management and graphics.

The remainder of this section will describe  the  display  process  in
general (and not always immediately defined) terms.

The basic displayable  object  is  a  "virtual  display."  This  is  a
rectangular  area  which  can be associated with (made visible on) the
screen of a video display  device.   A  virtual  display  can  have  a
"banner"   (identifying  information),  a  "border"  (a  pattern  that
outlines the virtual display), a "picture area"  (the  inside  of  the
display  where  information  can  be  shown), and up to four "margins"
(space between the border and the picture area).

The simplest kind of information display involves creating  a  virtual
display  and  writing  text  into its picture area by using the normal
COMMON LISP stream output operations.

The next level of complexity involves doing  graphical  operations  to
the picture area of a virtual display.  Graphical operations are those
which (loosely  speaking)  produce  non-text  images  in  the  virtual
display.   They include operations such as drawing lines and polygons,
filling areas with some pattern,  and  putting  graphical  symbols  at
COMMON LISP Graphics Models                                     Page 3

Graphical operations usually require one or more pairs of  coordinates
to  give  the  location(s) of the output.  A virtual display's picture
area has a coordinate system with its origin  (location  0,0)  at  the
lower  left corner.  The location of points in the picture area can be
given by specifying offsets into the picture area along the horizontal
(X)  and  vertical  (Y) axes.  These offsets, as well as the bounds of
the picture area, are expressed in centimeters.

All supported graphics operations can be done directly  in  a  virtual
display,  as long as the coordinates are restricted to those that fall
roughly within the bounds of the picture area.  However, not all  data
in  the  world  falls numerically within the bounds of a picture area.
For example, a physicist might want to graph pion production rate  vs.
impact energy in furlongs per fortnight.  In order to present a visual
depiction, the data (in both axes) must be scaled  and  translated  in
order to fit into the bounded coordinate system of a picture area.  It
may also need to be rotated about some axis.  This process is known as
"coordinate transformation." What is required is a method that defines
the appropriate transformation and thus allows the user to express his
data  in  the  most convenient units.  The commonly selected method is
called the "window-viewport transformation."

A "window" is a rectangular area usually specified in  the  coordinate
system  of  the  user data.  This user coordinate system is called the
"application data space." The specification of a window  is  really  a
statement that says "all data of interest to me falls in this range."

A "viewport" is a rectangular area defined in the coordinate system in
which  the  graphical  representation  of  the  data  will  be kept or
displayed.  Such a coordinate  system  might  be  that  of  a  virtual
display,  with  the  viewport defined to be all or part of the virtual
display's  picture  area.   The  specification  of  a  viewport  is  a
statement  that  "this is where I want to see the pictorial view of my

At the simplest level, a window-viewport transformation might  involve
the  definition  of a window in a user's application data space and an
associated viewport which is the picture area of  a  virtual  display.
Now  the  user is free to draw lines and do other graphical operations
in the coordinate system of his data.  The results will appear in  the
picture area of the virtual display.

Now  that  the  transformation  operation  is   defined,   a   further
complication   can   be  introduced:   the  notion  of  "composition."
Composition means the building up of a graphical object in a  separate
coordinate  system  (the  "composition space").  In the previous case,
the picture area of a virtual display was used as a composition space.

There is no reason that the notion of composition cannot  be  combined
with  transformation  to  enable  production  of  arbitrarily  complex
graphical systems.  For example,  the  Graphics  Kernel  System  (GKS)
defines  two levels of composition and transformation.  GKS comes with
a predefined composition space called  Normalized  Device  Coordinates
(NDC)  which  has  bounds  at (0.0,0.0) and (1.0,1.0).  The user first
COMMON LISP Graphics Models                                     Page 4

specifies a transformation from application data space into NDC.  Then
additional transformations are created which map portions of NDC space
onto  the  physical  device  screen  (which  is  treated  as   another
composition space).

This complexity can be increased since this  process  can  go  to  any
level if the user is allowed to create independent composition spaces.
The graphics world has created the concept of "segments" to  represent
independent   composition   spaces.    These  composition  spaces  are
typically mapped onto multiple viewports so that  a  single  graphical
object  may be viewed simultaneously in many places.  For example, the
symbol for a NAND gate is drawn in an  independent  composition  space
which is then mapped into multiple places in a circuit diagram.

"Display management" refers to the means supplied to position  virtual
displays  on  the  screen  and  to  determine  which shall be visible.
Virtual displays are made visible on the screen  by  associating  them
with the screen.  Since virtual displays are opaque, they can hide, or
"occlude," other virtual displays.  The display management system must
therefore  determine  which  virtual display will be occluded when two
overlap on the  screen.   The  system  does  this  by  consulting  the
"stacking  order"  to  see  when  each display was associated with the
device.  The position of a virtual display in the stacking  order  can
be  altered,  or  the virtual display can be removed from the stacking
order altogether.

The display management system must also provide means to move  virtual
displays on the screen and to change their shape and size.

A pointing system allows the user to move a cursor around  the  screen
in  order  to indicate positions where operations should take place or
to choose some object (such as a menu selection) from a display.   The
positioning  operation  is  called "pointing" and the process of using
the pointing system to choose an object is called  "picking."  Certain
areas  of  the  display can be made sensitive to the pointing system's
cursor so that an action can be triggered when the  cursor  enters  or
leaves the sensitive area.

With this introduction, the remainder of the paper  goes  on  to  more
rigorously  define  these and other concepts of a possible COMMON LISP
graphics and display model.


Much of the confusion around displays, graphics, bitmaps, etc.  has to
do   with   the   use   of   different   coordinate  systems  and  the
transformations between them.  Several coordinate systems will be used
in later discussions.  Some of the important ones are defined here.
COMMON LISP Graphics Models                                     Page 5

3.1  Application, World, User Coordinates

These terms all loosely refer  to  the  same  idea  of  an  unbounded,
N-dimensional  space of floating-point numbers, where N is typically 2
or 3.  As used in graphics systems, these terms really  refer  to  the
coordinate system in which some particular set of graphical operations
(draw line, draw point, etc.) is performed.  Another  way  of  stating
this is that these are the most convenient coordinates in which a user
can graphically describe his data.

For example, for a graph  of  volume  of  sales  by  year,  it's  most
convenient  for  the  user  to give the data to the graphics system as
number pairs representing millions per year.  The graphics  system  is
then   responsible  for  eventually  transforming  this  data  to  the
coordinates of the display device and displaying it.

There is no  composition  implied  by  the  specification  of  several
graphical   objects   in  overlapping  application  coordinates.   For
example, several objects may be drawn in a range of  coordinates  from
(1.0,1000.0)  to (5.0,1000.5) and yet they will not appear together in
the display if they are directed to different composition spaces.

All output operations are specified in application data space and  are
transformed  into  a  composition  space.  This implies that there can
only be a single "active transformation" in effect at any given  time.
(See  Transformation  Operations  for  more  information on the active

This paper will use the term "application data space"  when  referring
to  the  coordinate  system  in  which  the  user  performs  the basic
graphical operations that build an object.

3.2  Master, Object Coordinates

These terms refer to the coordinate system defined by some composition
space  used  to  describe  a  particular  object.  The coordinates are
expressed as floating-point numbers.  This new object may be a part of
a larger drawing in one or more different composition spaces.

This paper will use  the  term  "master  coordinates"  for  coordinate
systems used in this way.

3.3  Physical Device Coordinates

Physical  device   coordinates   consist   of   a   bounded   set   of
two-dimensional  integer  coordinates  that  specify  the  addressable
positions of an output device's display area.  The device  coordinates
themselves  do  not  specify the absolute size of an addressable unit.
The unit may be a pixel on a bitmap terminal, or a character cell on a
character  terminal.   Each implementation must supply functions which
COMMON LISP Graphics Models                                     Page 6

give the physical size of the addressable units  of  the  device,  for
example,  the height and width of a pixel.  This allows users who wish
to work in the physical units of the device to scale their coordinates

The numeric range of each axis  is  defined  by  the  physical  device
itself,  as  are  the  location of the origin and the direction of the
axes.  For example, a character terminal may have an origin  at  (1,1)
in  the  upper left corner of the screen with the X bound of 80 or 132
and the Y bound of 24.  A  particular  bitmap  terminal  may  have  an
origin  at  (0,0)  in the lower left corner with X and Y ranges of 767
and 468.

3.4  Logical Device Coordinates

Logical  device  coordinates  are  two-dimensional  coordinates   with
floating-point   values.    Logical  device  coordinates  specify,  in
centimeters, locations on a "logical device" which is  independent  of
the   particular   physical   display  device.   Furthermore,  logical
coordinates always have a (0,0) origin at the lower left corner of the
display  screen.   The  logical display screen thus corresponds to the
upper right quadrant of a conventional X-Y coordinate system.

Since  logical  device  coordinates  always  specify  measurements  in
centimeters,  an  object  or  display  that is described using logical
device coordinates will have the same size and  shape  on  any  output
device.  Users who wish to work in physical device coordinates can use
the functions that give the size of a physical device unit to  control
the size and shape of their images.  (See Physical Device Coordinates,

This paper will always use the term "device coordinates" in the  sense
of "logical device coordinates" unless otherwise stated.

3.5  Virtual Display Coordinates

Virtual  display  coordinates   are   two-dimensional   floating-point
coordinates  that  specify  locations  within  a virtual display.  The
units of the virtual display coordinates are the same as the units  of
the logical device coordinates, that is, centimeters.

Since virtual display coordinates and logical device coordinates share
the  same  units and since both have origins in the lower left corner,
the position of a point in a virtual display on the logical display is
a  pure  translation  of  that  point  from  the origin of the logical
display coordinate  system.   In  other  words,  only  translation  is
required  when  placing  or  shifting a virtual display on the logical
device; no scaling or rotation is needed.
COMMON LISP Graphics Models                                     Page 7

3.6  Normalized Device Coordinates (NDC)

This is a term  commonly  defined  by  the  implementors  of  graphics
systems.    Normalized   Display  Coordinates  describe  an  idealized
graphics display device that has a square display and an aspect  ratio
of  1  (meaning that a mathematical square is "displayed" as a square,
not  a  rectangle).   Locations  in  this  display  are  specified  by
coordinates  whose X and Y values can be floating-point numbers in the
range of 0.0 to 1.0, inclusive.  The origin in the NDC  system  is  at
the lower left of the display.

By using Normalized Device Coordinates, all graphics  data  is  mapped
into NDC space before mapping to the physical device.  In the Graphics
Kernel System (GKS), NDC  space  provides  both  a  device-independent
coordinate mapping and a graphical composition layer.
COMMON LISP Graphics Models                                     Page 8


Transformation  (or  coordinate  transformation)  is  the   one-to-one
mathematical  mapping  of  points in one coordinate system to those in
another.  In the current context, transformation is limited to  linear
operations of scaling, rotation, and translation.  Projection (mapping
of an N-dimensional space onto N-1 or fewer dimensions) is not treated
in  this document.  The remaining discussions are therefore limited to
two dimensions, although nothing in the design should prohibit a  user
from  defining  N-dimensional transformations and implementing his own
projection algorithms for treating higher dimensional graphics.

See Chapter 7  of  "Fundamentals  of  Interactive  Computer  Graphics"
(Foley   and   Van  Dam)  for  a  thorough  discussion  of  coordinate
transformations in graphics systems.

4.1  Rotation

Rotation is the mapping of points  (x,y)  to  points  (x',y')  by  the

     x' = x * cos(a) - y * sin(a)
     y' = x * sin(a) + y * cos(a)

where a is the angle  of  counterclockwise  rotation.   Visually,  the
entire picture is rotated by the angle a.  Rotation is always computed
around the coordinate origin.  Aspect ratio is always preserved  under
a rotation transformation.

4.2  Scaling

Scaling is a  mapping  of  points  (x,y)  to  points  (x',y')  by  the

     x' = x * x←factor
     y' = y * y←factor

where x←factor and y←factor are  constant  terms.   Visually,  scaling
produces  an  enlargement  or  diminishment  of the plotted data along
either axis.  Aspect ratio (the ratio of the sizes  of  the  x  and  y
axes) is preserved only when x←factor = y←factor.

4.3  Translation

Translation is the mapping of points (x,y) to points  (x',y')  by  the

COMMON LISP Graphics Models                                     Page 9

     x' = x + x←offset
     y' = y + y←offset

where x←offset and y←offset are constant terms.  Visually, the  entire
picture is moved intact to another location.


5.1  Matrix Representation

All points in the  graphics  system  are  represented  in  homogeneous
coordinates.   Therefore,  all  transformations in N-dimensional space
may be represented by an (N+1)-dimensional square matrix.  The  actual
mapping of points (x,y) to points (x',y') may be carried out using the
following equation:

     [x', y', 1] = [x, y, 1] *  | r11 r12  0 |
                                | r21 r22  0 |
                                | t1  t2   1 |

which reduces to two equations involving a total of four multiply  and
four add operations.

Transformations in COMMON LISP will be treated as LISP  objects  which
may    contain    these   specialized   N-dimensional   matrices.    A
transformation object can be created by specifying  a  window-viewport
pair  and  adding rotation information, if any.  The user will also be
allowed to create transformation objects to suit his own needs.   This
latter    capability   is   important,   since   the   window-viewport
transformation only  produces  scaling  and  translation  without  any
rotation  capability.  Also, the transformation manipulation functions
will accept N-dimensional transformation objects and are likely to  be
more efficient than user-written matrix multiplication code.

A  transformation  object  may  also  be  defined  which  involves   a
user-written  function  that  will  be called when a transformation is
required.   This  feature  may  be  used  to  allow  users  to   write
3-dimensional projection and clipping transformations.

5.2  Window-Viewport Transformation

A window is a rectangle whose limits (vertices) are defined in  a  set
of  coordinates  which  may  lie  in application data space or in some
defined composition space.  Conceptually, a window  functions  like  a
"window"   in  the  real  world  (the  glass  variety).   It  opens  a
rectangular area in some coordinate space so that any data which falls
within  the  limits  of the window may be made visible to the user.  A
window may specifically delete data that falls outside its limits;  in
this  case it is a clipping rectangle (see Clipping Rectangle, below).
If clipping is not enabled, data that falls  outside  the  window  may
COMMON LISP Graphics Models                                    Page 10

still be visible.

In conjunction with a viewport, a window is used to provide a  scaling
and  translation  transformation.   This  is  a conventional method in
graphics to specify a coordinate transformation.

A viewport is a rectangle whose limits are  defined  in  a  coordinate
system  that must lie in some defined composition space.  The viewport
serves two functions:

      o  It defines where in the composition space the data  or  other
         information will appear.

      o  When associated  with  a  window,  it  defines  a  coordinate
         transformation  specification  and  also  indicates that data
         "seen through" that particular  window  will  appear  in  the

5.3  Active Transformation

All  graphics  operations  must  be  applied  with  respect  to   some
transformation.   For  example,  a line is drawn by specifying the end
points  of  the  line.   The  coordinates  of  these  points  may   be
transformed  into the master system of some object which is being used
in a composite display, or directly into the picture area of a virtual
display.   In  the  first case, the transformation may be an elaborate
one which includes multiple  levels  of  scaling  and  rotation.   The
latter may only involve a simple translation of points relative to the
origin of the logical device coordinates.

All of the output functions  which  require  positioning  information,
such  as  line  drawing and character insertion, will take an optional
transformation argument.  The default value of this argument  will  be
the   currently   specified   active   transformation.    The   active
transformation is no different from any  other  transformation  except
that  it  has  been  designated  to  be the default transformation for
output operations.  The system should provide a  function  similar  to
the  COMMON LISP IN-PACKAGE function which sets the value of a special
variable which is the active transformation.  In addition, the  system
may  have  a  macro (WITH-TRANSFORMATION) which binds the value of the
current transformation within some scope.


A clipping rectangle is a rectangle defined  as  a  window  either  in
application data space or in a composition space.  Clipping is part of
the transformation operation.  It is usually done in  the  originating
coordinate  system.   The  purpose  of  clipping is to remove from the
display any portions  of  a  graphical  image  that  lie  outside  the
clipping rectangle.  Thus, if the user specification of a line has end
COMMON LISP Graphics Models                                    Page 11

points which are outside the rectangle and clipping is  enabled,  only
the portion of the line that falls within the rectangle will be mapped
onto the destination composition space.  If clipping is  not  enabled,
the entire line will be mapped.

In the destination coordinate system, clipping is  performed  only  at
the  boundaries  of  the physical device.  (A viewport cannot define a
clipping rectangle.) Since physical device coordinates are  a  bounded
coordinate  system,  any  points  which  lie outside the bounds of the
physical device will be unconditionally clipped.

Clipping can be enabled or disabled on a  global  basis  or  for  each
graphical output operation.


Composition is the process of building complex graphical objects  from
(potentially)  a  number  of different objects and coordinate systems.
Conceptually, composition is akin to placing various graphical objects
onto some flat surface in a particular arrangement.  This flat surface
is termed a composition space.  Windows can then  select  portions  of
this  flat  space either for viewing on the screen or for use in other
composition spaces.

A simple example of composition is the definition of the symbol for  a
NAND  gate.   The symbol is created in its own master coordinates.  It
is then mapped onto various parts of  another  composition  space  and
lines are drawn using a different transformation into that composition
space to connect the symbols into a circuit diagram.

7.1  Composition Space

A composition space is an independent data  space  which  has  certain
special characteristics:

      o  It can store graphical objects.

      o  It can optionally  define  a  rectangle  which  may  be  used
         simultaneously  as  a  window,  a  viewport,  and  a clipping

Mapping from application data space or from a composition  space  onto
another  composition  space  is  accomplished  by  specifying either a
window-viewport pair (plus rotation) or by explicitly providing source
and  destination  spaces  plus  a transformation matrix and a clipping

Portions of a composition space  can  be  further  mapped  onto  other
composition  spaces  to an arbitrary depth; and composition spaces can
be recursively mapped to themselves.   When  a  composition  space  is
COMMON LISP Graphics Models                                    Page 12

mapped  onto  other  composition  spaces, changes made in the original
composition space appear in all the composition spaces  it  is  mapped
onto.   By contrast, the contents of a composition space can be copied
to other composition spaces.   Any  subsequent  changes  made  in  the
original composition space will not be reflected in the copies.

7.2  Segments

"Segment" is a term used in conventional graphics systems to denote an
independently  specified  graphical  object.   Segments  are  built in
independent composition spaces.  Segments may be  used  together  with
other  graphical  objects  and  primitive  operations to create a more
complex graphical object.

The creation  and  use  of  segments  is  entirely  analogous  to  the
segmentation of programs into subroutines which may be used repeatedly
by different code segments.  The building process is not confined to a
single  level.   Segments  may  be  composed of other segments and the
entire object then used  as  a  portion  of  a  larger  diagram.   The
graphics   system   handles   the  nested  coordinate  transformations
necessary to produce the levels of graphical object.

A significant feature of a segment is that it is created once and  may
then  be  mapped  (via additional transformations) any number of times
into different composition spaces.  An example of  a  segment  is  the
symbol  for  a  NAND gate.  This symbol need only be defined once.  It
can then be mapped any number of times to create  a  circuit  diagram.
Note  that  if  the  original  NAND  gate  symbol  is changed, all the
mappings of it automatically change.  Furthermore,  any  change  to  a
transformation  between  one  space  and  another  propagates into any
further mappings.  For example, if the  window  surrounding  the  NAND
gate  segment  is  made larger, the NAND gate will appear to shrink in
each viewport mapped to that window.  The graphics system handles  all
intermediate  levels  of  coordinate  transformation needed to map the

Segments may be copied rather than mapped, in  which  case  they  lose
their  reference to the original object.  Changes in the original will
not affect any copies made from it.

Segments may be returned as  the  result  of  a  pick  operation  (see
Pointing and Picking).

7.3  Virtual Display Composition

Since virtual displays are themselves composition spaces (see  Virtual
Displays),  they can be mapped onto other composition spaces.  This is
particularly useful when making a virtual display that is a  composite
of other virtual displays.  Such a composite display can be treated as
a single display for display management purposes, and yet each display
COMMON LISP Graphics Models                                    Page 13

can  retain  its  own identity for all other operations.  Some systems
call this a "pane" system with the final composite  display  called  a

7.4  COMMON LISP Composition Levels

COMMON  LISP  should  allow  for  creation  of  arbitrary  levels   of
composition.  One that will be provided by default is:

      o  Virtual display space (allowing virtual displays to be mapped
         into the picture area of another virtual display)


Attributes are parameters that affect  the  visual  representation  of
output  operations.   They  can, for example, determine the background
color of a composition space, the width and pattern  of  a  line,  the
font  and  spacing  of  text,  or the visibility of a graphical object
mapped onto some composition space.

Some attributes are inherently "static" while  others  are  inherently
"dynamic."  When dynamic attributes are changed, the visual results of
previous  operations  that  used  those  attributes  will  immediately
change.  Operations done with static attributes must be re-executed in
order to change the visual appearance of their results.

Some attributes are naturally  associated  with  types  of  operations
(such as graphics primitives) while others are associated with objects
(such as composition  spaces).   Some  can  be  associated  with  both
objects  and operations.  For example, a composition space can have an
attribute that specifies the default color of all operations that take
place  within  it,  and an individual graphics operation can specify a
color attribute to override the default.

Attributes are also organized in blocks.  (GKS calls attribute  blocks
"bundles.")   Attribute  blocks  can  be  associated  with  individual
operations,  transformations,  or  composition  spaces.   Nesting   of
transformations implies some form of attribute nesting as well.

8.1  Attribute Descriptions

Attributes can be categorized by the type of operation or object  they
affect,   although   this   categorization   is  more  for  conceptual
convenience than  to  suggest  a  meaningful  difference  between  the
attributes.   The  following  is  a  suggested  list of categories for
COMMON LISP attributes:

     Composition space
COMMON LISP Graphics Models                                    Page 14


Attributes associated with a composition space  serve  two  functions:
they  describe  attributes  of  the composition space itself, and they
also provide a complete set of default attributes for any graphics  or
text   operations  done  into  that  space.   These  defaults  can  be
overridden by  attributes  applied  to  individual  graphics  or  text

The  following  possible  attributes  which  will  be  considered  for
inclusion  in  a  possible COMMON LISP graphics model are listed under
the categories described above.  These attributes are all described in
terms  of  bitmapped  terminals.   Some of the attributes may function
differently - or not function at all - on other  types  of  terminals,
such  as character terminals.  The specific behavior of each attribute
on various terminals is implementation-dependent.

      o  Composition Space  Attributes  -  the  first  two  attributes
         determine  characteristics  of  the composition space itself,
         while the second two establish defaults for graphics or  text
         operations done in the space.

          -  Visibility - specifies whether operations done into  this
             space  (when  it  is  mapped  into some other composition
             space) will be immediately visible or  deferred  until  a
             later time.

          -  Background Color - specifies the background color of  the
             composition space.

          -  Drawing Color - specifies the default color to be applied
             to all output operations into this space.

          -  Writing Mode - specifies the relationship applied  to  an
             output  operation  and  the  existing  bitmap  pattern to
             produce the resulting display rendition:

                  NIL - operation is performed (information is kept in
                  the  display  list)  but  the  output display is not

                  :XOR,  :OR,  :ORC1,  :AND,  :ANDC1  -  the   Boolean
                  operation  that  is applied to the bitmap pattern of
                  the operation and the  existing  bitmap  pattern  to
                  produce  the  displayed  result.   The C1 forms mean
                  that the bitmap produced by the operation  is  first
                  complemented   before   the   logical  operation  is
                  performed with the existing bitmap.

                  :REPLACE, :COMPLEMENT-REPLACE - the  result  of  the
                  operation  (or  its  complement) completely replaces
                  the affected contents of the display.
COMMON LISP Graphics Models                                    Page 15

                  :ERASE,  :COMPLEMENT-ERASE  -  the  result  of   the
                  operation is completely replaced with the background
                  color (or its complement) of the composition space

      o  Graphics  Attributes  -  these  attributes   are   associated
         specifically  with  graphics  operations.   They  can also be
         applied to a composition  space  to  determine  defaults  for
         graphics operations in that space.

          -  Line Width - specifies the  width  of  a  displayed  line
             expressed  as  a (floating-point) multiple of the minimum
             width that the device can draw.

          -  Line Style - specifies the particular visual style of the
             line  to  be drawn.  The following are suggested although
             implementations may vary in the types available:


          -  Fill - specifies whether or not objects are to be filled,
             the fill pattern to use, and the fill reference point.

          -  Marker Symbol - specifies the visual symbol used  by  the
             graphics operations which place marker symbols at points.
             The symbol is centered on the specified point.   Supplied
             symbols are implementation dependent.

      o  Text   Attributes   -   these   attributes   are   associated
         specifically  with text operations.  They can also be applied
         to  a  composition  space  to  determine  defaults  for  text
         operations in that space.

          -  Font - specifies the font set to  be  used  when  writing
             text.  Values are implementation dependent.

          -  Character  Spacing  -  alters  the  normal   spacing   of
             character  writing.   This  attribute  is  expressed as a
             floating-point number that is multiplied by the character
             height to produce additional space to be inserted between
             characters.  The number can be negative,  in  which  case
             characters may be forced closer together or overlapped.

          -  Character Slant - slants fonts to produce  italics.   The
             slant  is expressed in degrees and should be in the range
             of -45 to +45.

          -  Base  Line  Angle  -  specifies  the  angle  of   writing
             characters.    This   attribute   is   expressed   as   a
             floating-point number representing  degrees  of  rotation
             from  the  normal  horizontal.  Unslanted characters will
COMMON LISP Graphics Models                                    Page 16

             always appear to be vertical when viewed  from  an  angle
             parallel to the base line.

          -  Text Path - specifies the direction of character  writing
             in  relation  to  the base line.  There are four possible

                  :FORWARD - this is the normal left-to-right  display
                  of  characters  in  a direction parallel to the base

                  :BACKWARD - this is  the  reverse  of  the  :FORWARD
                  direction  and  is  used,  for example, when writing
                  Hebrew text.

                  :UP - characters are displayed sequentially  "above"
                  each other in relation to the base line.

                  :DOWN - the reverse of :UP; characters are displayed
                  sequentially  "below"  each other in relation to the
                  base line.

          -  Texture - a bitmap pattern which is logically ANDed  with
             a character bitmap before writing to the display.

An implementation is free to designate  supported  attributes  and  to
categorize any supported attributes as static or dynamic.

8.2  Attribute Inheritance

Every composition space has a default attribute block associated  with
it.   This  block  must  contain  a  complete specification of all the
supported  attributes  for  an  implementation.   In  general,   these
attributes may be overridden on a per-operation basis.

A set of operations into some composition space may be performed  with
respect  to some other attribute block.  This block may be incomplete.
Any required attribute values will be taken either  from  an  explicit
value in a specific operation or from the default attribute block.

Attribute  inheritance  in  the  presence  of   multiple   levels   of
composition  is not well understood.  Static attributes may be treated
easily since the visual results of a  performed  operation  cannot  be
changed  without  re-executing  the  operation.  Proper inheritance of
dynamic attributes, however, is more difficult to determine.  At  this
point,   the  inheritance  of  dynamic  attributes  is  implementation
COMMON LISP Graphics Models                                    Page 17


A virtual display is a specialized graphical object  used  to  display
graphics  or  text  information  on a physical device.  It is the only
type of graphics object which can be displayed on a device.

A virtual display is made visible on a device by associating  it  with
that  device,  although  a  virtual  display  can  exist without being
associated with any device.  Associating  a  virtual  display  with  a
device  is  similar  to,  but  not  the  same operation as, creating a
mapping from one composition space to another.  A major difference  is
that  virtual  displays  are opaque; that is, the order of association
affects the visible result on the device.   If  two  virtual  displays
overlap on the screen, the portion of the first which is overlapped by
the second will not be  visible.   Normal  mappings  onto  composition
spaces  are  transparent,  that  is, all operations are always visible
(see Display Management).

Creation of a virtual display creates a composition space onto which a
number  of  graphical  objects are mapped.  These objects have default
spatial relationships which can be altered at  the  time  the  virtual
display  is created.  The following diagram illustrates the objects of
a virtual display in a typical configuration.  All objects except  the
picture area are optional.

     Banner  +--------------------------+
     area    |    Banner area           |
             =                          =   |
             = +----------------------+ =<--Borders
             = |                      | =
             = |    Picture area      | =
             = |                      | =
             = |                      | =
             = | Picture area         | =
             = | origin               | =
             = |/                     | <--Margins
             = +----------------------+ =  |
             =                          <--+
     Virtual display origin

Each of the objects shown will be discussed in greater detail later in
this section.

The mapping of a virtual display's objects into its composition  space
produce  transformations  which  can  be  used  during I/O operations.
Additional arbitrary transformations into this composition  space  can
be created as needed.
COMMON LISP Graphics Models                                    Page 18

To create a virtual display, one specifies the  size  of  its  picture
area  along  with  the  size  and spatial relationship of any optional
parts.  The total size of the virtual  display  is  the  size  of  the
picture area as extended by the optional parts.

9.1  Composition Space

The creation of a  virtual  display  results  in  the  creation  of  a
composition  space  within  which  the virtual display is built.  This
space may be used in all respects  as  any  other  composition  space;
users can do arbitrary graphical operations within it.

9.2  Picture Area

The picture area of a virtual display is the  rectangular  area  where
data is normally displayed.  It is a window-viewport pair which maps a
portion of application data space into the composition  space  of  the
virtual  display.  The size of the viewport is the size specified when
the virtual display was created.  By default, the window is  the  same
size  and  has  the  same coordinate system as the viewport; thus, the
transformation is trivial.  A different window may be  specified  when
the  display is created.  Unless otherwise specified, the picture area
viewport has a coordinate origin at the lower left corner and  a  size
expressed  in  virtual  display units (centimeters).  The picture area
has  a  transformation  object  which  may  be  used  as  the   active
transformation in any graphics operation.

The other objects of a virtual display are placed in a  fixed  spatial
relationship  to  the  sides of the picture area.  If the picture area
grows or shrinks, the margins, border, and banner  area  move  on  the
screen to maintain this relationship.

9.3  Banner Area

The banner area is an optional part  of  a  virtual  display.   It  is
similar to the picture area in that it is defined as a window-viewport
pair.  The  viewport  is  mapped  into  the  composition  space  in  a
particular  spatial  relation  to  the picture area.  It may be above,
below, or to the right or left of the picture area.  It  is  separated
from  the  picture area by the width of the margin and border.  Unless
otherwise specified, the banner area viewport has a coordinate  origin
at  the  lower  left corner.  Its width (or height if the banner is to
the right or left) is, by  default,  the  width  (or  height)  of  the
picture  area viewport plus the width of any margins and borders.  The
banner area has a transformation object  which  may  be  used  as  the
active transformation in any graphical operation.
COMMON LISP Graphics Models                                    Page 19

9.4  Border

A virtual display may optionally have a  border.   The  border  is  an
outline  of  the  picture area, separated from the picture area by the
margins.  Its width is specified in virtual  display  units.   In  its
most  basic  form,  the  border  may  be  a line of some default width
surrounding the picture area.  If supporting hardware permits, it  may
have  an  arbitrary  thickness  and  tile  pattern (see Bitmaps).  The
border may be designated as a sensitive area for the pointing system.

9.5  Margin

The margin is the space between the border and the picture area; there
can  be  four  margins associated with a virtual display.  Its size is
measured in virtual display units.  The default size of any margin  is
implementation dependent.

Margins are  most  often  used  to  separate  text  from  the  border.
However,  some  set of implementation dependent operations may also be
performed in the margins of a  display,  such  as  drawing  lines  for
scroll  bars.   The  margins  lie outside the coordinate system of the
picture area; they must be accessed by using the coordinate system  of
the virtual display composition space.

9.6  Virtual Display Window

The entire rectangle encompassing the picture area, banner, border and
margins  of  a  virtual display is enclosed in a window in the virtual
display composition space.  This window may be used to map the display
onto a physical device or into some other composition space.  The size
of this window tracks the "size" of the virtual display, such that if,
for example, the picture area viewport is changed, the virtual display
window is automatically adjusted.

9.7  Device Viewport

A device viewport is a specification, in logical  device  coordinates,
of  the  size  and location of a virtual display on a physical device.
Unless otherwise specified, the size of a device viewport is the  same
size as the virtual display window.  The transformation is then a pure
translation.  An arbitrary transformation may be applied to scale  and
rotate the appearance of the virtual display on the screen.

9.8  LISP Terminal Streams To Virtual Devices

A virtual display may be used as an argument to the various  varieties
COMMON LISP Graphics Models                                    Page 20

of MAKE-STREAM functions that exist in COMMON LISP.  Such a stream can
be input, output, or both.  A virtual display stream opened for output
means  that  printed  LISP  output  will  be  directed to that virtual
display.  An input stream designation means that a LISP read operation
on that stream will get input from the keyboard device attached to the
terminal.  An input-output stream reads characters from  the  keyboard
and  echoes those characters in that virtual display.  All designation
of font, spacing,  color,  etc.   is  specified  in  attribute  blocks
associated with that virtual display.

The physical device need not be  a  keyboard,  although  that  is  the
normal  device.   It may be any device capable of responding correctly
to the COMMON LISP input operations.  This allows, for example, a file
to  be associated with one display and the keyboard with another.  The
resulting effects on the screen (and to the program)  depend  only  on
the choice of virtual display used in the input operation.

9.9  Input Cursor

Each virtual display which has an associated virtual input device will
have   an  input  cursor  defined.   The  nature  of  this  cursor  is
implementation dependent but it must at least provide  an  indication,
when  this  display  is  being used for input, of the current location
where echoed input will appear.  This cursor is  often  distinct  from
the pointing (or mouse) cursor.


In a virtual display and graphics environment, it is  often  necessary
to  translate a visually perceived location on the display device into
information  useful  to  the  running  program.   Operations  such  as
selecting  an  item from a menu, indicating a virtual display to bring
to the top of the stacking order, and selecting a gate connection in a
circuit diagram are all examples of pointing or picking.

Pointing and picking are input operations that require a certain level
of  physical device support.  The device must be capable of generating
a visual indicator (cursor) which indicates a screen position, and  it
must have a means of manipulating the position of this indicator.  The
manipulation need not be independent from  the  host  processor.   For
example, the arrow keys on a character-oriented terminal might be used
to request the host processor to move the cursor to different spots on
the  screen.   Other supporting devices can be various forms of mouse,
light pen, tablet and cross-hair.

The distinction between pointing and picking is in the nature  of  the
object  returned  as  a  result  of  the  operation.   The result of a
pointing operation is always an N-dimensional (usually 2)  coordinate.
The  result  of  a picking operation is a previously defined graphical
object.  This might be a simple object such as a line or it might be a
COMMON LISP Graphics Models                                    Page 21

composition space which makes up a part of the display.

A pointing or picking operation is always performed  with  respect  to
some  transformation.  This transformation is used to specify both the
coordinate system in which the results are expressed and the level  of
detail  required of the operation.  For example, a pick might return a
particular mapping of a NAND gate symbol, the  NAND  gate  composition
space,  or  a portion of the NAND gate symbol, depending on the chosen

Both pointing and picking are primarily input operations but may  also
involve  placement  of  the  position  cursor  using  the  appropriate
coordinate  system.   The  input  operations  are   completed   in   a
device-dependent  fashion, such as clicking a mouse button or pressing
a function key on the terminal.

Rectangular sections of the  screen  can  be  made  sensitive  to  the
pointing cursor.  Section 11.2 discusses this concept.

10.1  Pointing

Pointing is an input operation  that  returns  a  coordinate  in  some
N-dimensional  space.   The  space  must  be  previously defined.  For
example, the  coordinate  may  be  an  X-Y  pair  of  physical  device
coordinates.   It  may  also  be a coordinate in the master coordinate
system of some defined graphical object.

10.2  Picking

Picking is an  input  operation  that  returns  a  previously  defined
graphical  object.  Such an object might be an entire virtual display,
for instance, when selecting a display to bring  to  the  top  of  the
stacking  order.   It  might  also  be  some  component of a graphical
object, such as a point, a line, or a segment.


"Display  management"  refers  to   the   facilities   available   for
controlling  the  appearance of the physical screen and making virtual
displays visible to the user.  Since virtual displays are opaque  when
placed  onto  a  physical  screen, they behave like cards stacked on a
table.  Portions of the screen that are covered by the rectangle of  a
virtual  display are not visible while that display is visible.  Thus,
a virtual display may hide (or "occlude") portions  of  other  virtual
displays  which  were  already  on the screen.  The display management
system must have the capability  to  place  virtual  displays  on  the
screen  and remove them from the screen.  The system must also be able
to move virtual displays on  the  screen  and  change  their  stacking
COMMON LISP Graphics Models                                    Page 22


Other display management capabilities  arise  from  the  necessity  to
provide  a  flexible  and  powerful user interface.  Since the display
system  should  have  some  type  of  pointing  device,  the   display
management  system must allow the programmer to define all or portions
of a virtual display as being sensitive to the pointing device.   This
means  the the user's software can detect whenever the pointing device
enters or leaves some selected area of a virtual display.  The  system
must  also provide for normal terminal I/O to be performed to and from
a virtual display.

11.1  Visibility And Stacking

A virtual display is a graphical object which may become visible on  a
terminal  screen.   It  can  exist  without  being associated with any
device or it may be associated with several devices simultaneously.

The display management system remembers the order  in  which  displays
are  associated with each device.  Associating several displays with a
device is called "stacking" since it is analogous to stacking up cards
on  a  flat surface; the order in which displays are associated with a
particular device  is  called  that  device's  "stacking  order."  The
position of a display in the stacking order can be altered.  It can be
brought to the top, pushed to the bottom, or  placed  above  or  below
another  virtual display in the stacking order.  If a display is moved
on the display screen, it  maintains  its  position  in  the  stacking

The stacking order is important  to  the  appearance  of  the  screen,
because  it helps determine which displays can hide other displays.  A
virtual display is said to be "occluded"  on  some  device  if  it  is
beneath  another virtual display in the stacking order for that device
and if some or all of its area is within the screen area  occupied  by
the other virtual display.

A virtual display, in addition to being associated with a device,  may
also   be   "exposed"  (rendered  visible)  or  "unexposed"  (rendered
invisible) on that device.  In order  for  a  virtual  display  to  be
visible  to  the  user on some device, it must be associated with that
device, be exposed, and not be  entirely  occluded  by  other  exposed
virtual  displays.   A  display can be made invisible but preserve its
position in the stacking order by making it unexposed.  In this state,
it cannot occlude other virtual displays.

Exposure is a property of an element (virtual display) in a particular
stacking  order,  not  a  property  of the element itself.  Since each
display device has its own stacking order, a display may be associated
with more than one device but be exposed on only some of the devices.
COMMON LISP Graphics Models                                    Page 23

11.2  Sensitive Regions

Rectangular areas of a virtual display may be made  sensitive  to  the
pointing  device.   A  sensitive  region is defined in virtual display
coordinates by specifying the lower left corner  and  the  height  and
width of the rectangle.

Designating a region as sensitive provides the programmer with several
capabilities for creating a user interface to the display system:

      o  The visual appearance of the sensitive region can be  altered
         either  automatically  when  the  pointing  device  enters or
         leaves the region,  or  under  program  control  without  the
         pointer moving at all.

      o  A LISP  function  can  be  invoked  asynchronously  when  the
         pointing device enters or leaves the region.

      o  The sensitive region can be returned as the result of a  user
         selection among a list of sensitive regions.

11.3  Menus

All display management systems should provide for a  special  type  of
virtual display called a "menu." There can be many types of menus, but
one kind should be provided with all Common LISP systems.  This  is  a
simple  choice  menu.   The  display  appears  as  a  vertical list of
options.  The pointing device is used to point to a desired  item  and
the  item  is  selected in an implementation-dependent fashion.  There
must be LISP functions which allow the programmer to create  the  menu
(providing both the selectable items and the value to be returned from
selection of each item) and to display the menu and query the user for
an  item  selection.   All  of  the usual display management functions
operate correctly on menus.

11.4  Pointer And Selection

Each implementation must provide a method for the user to "point" at a
particular location on the physical screen.  This might be implemented
with a mouse, light pen, cross hairs, or the cursor movement keys of a
simple  video  terminal.   This pointer should be able to indicate all
visible areas of the screen.

There must be a defined method of indicating  to  the  display  system
that  some  selection  has  been made relative to the pointing device.
The most common of these is the buttons on a mouse.  It  may  also  be
one or more special keys on the keyboard of the terminal device.  Each
implementation must define the number of selection  possibilities  and
the method for invoking each.
COMMON LISP Graphics Models                                    Page 24

Each implementation must also provide some way of indicating that  the
pointing device has moved.


Many video terminal devices operate by allocating  fixed-sized  blocks
of  display space (cells) for display of character and graphical data.
These  cells  are  individually  addressable  and  are  the   smallest
addressable  unit  from  the programmer's perspective.  Other graphics
devices  are  capable  of  doing  direct  vector  and  other   graphic
operations  on  the display.  Bitmapped terminals allow the programmer
to access individual pixels in the display directly.   The  method  of
access  is  to maintain a two-dimensional array of bits in memory that
directly controls the display of each pixel.  The array  is  called  a
bitmap.   All  operations to the terminal display are made by altering
the bitmap.

In any implementation that supports bitmapped  devices,  each  virtual
display  will have a bitmap and each device will have a device bitmap.
It will be possible to retrieve  all  or  portions  of  any  of  these
bitmaps  via  implementation-supplied  functions  as well as to create
bitmaps as  LISP  objects.   Functions  will  exist  to  do  arbitrary
operations  combining  bitmaps  (OR, AND, etc.).  These operations are
not clearly defined  at  this  time.   Suggestions  appreciated.   The
purpose of such bitmap operations is to provide special visual effects
such as shading and texturing.

∂09-Jan-85  1420	@MIT-MC:Henry%MIT-OZ@SCRC-RIVERSIDE 	Silence breaker   
Received: from MIT-MC.ARPA by SU-AI.ARPA with TCP; 9 Jan 85  14:19:18 PST
Received: from MIT-APIARY-3 by MIT-OZ via Chaosnet; 9 Jan 85 17:17-EST
Date: Wed, 9 Jan 85 17:17 EST
From: Henry Lieberman <Henry%MIT-OZ@SCRC-RIVERSIDE.ARPA>
Subject: Silence breaker
To: Cl-Windows@SU-AI.ARPA, Cl-Object-Oriented-Programming@SU-AI.ARPA,

As some of you may know, I am working on a kit for building menu-driven
graphical interfaces [such as document illustrators, circuit diagrammers,
etc.] called EzWin. The kit provides protocols for representing menu commands as
objects, mouse sensitivity and selection of graphical objects. It also tries to 
separate the functionality of commands from the interface techniques and allow
alternative interaction styles. It is at a level considerably above the "just
bits on the screen" one at which Boetje@Dec's proposal is aimed, but would be
complementary to such proposals. A wide range of interesting graphical interfaces
is easily specifiable using this approach. I hadn't designed it with a "language
standard" in mind, but perhaps standardizing things at this level as well might
productive, promoting portability of interfaces. 

I am currently preparing a paper on it for SigGraph '85. Interested people can
send me a message with US Mail address for a copy. It is too long for
transmission on this list and has many pictures.