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From: zap@lysator.liu.se (Zap Andersson)
Newsgroups: comp.graphics
Subject: Scene description: RayMond, comp.gfx's own scene description...:-)
Summary: C'est ne pas une summary
Keywords: Ray Scene
Message-ID: <625@lysator.liu.se>
Date: 9 May 91 06:47:30 GMT
Sender: news@isy.liu.se (Lord of the News)
Distribution: comp
Organization: Lysator Computer Club, Linkoping University, Sweden
Lines: 76

I think that a scene description language, empasizing the word SCENE, as
RenderMan does is problematic (not saying it's a Bad Thing). What I
propose is a Model description language, describing:

* Geometries
* Lights
* Semi-surfaces
* Named transformations that can later be changed ?

(The latter for the animation folks... :-)

Note the 'semi' on surfaces, that is a big hitch in renderers. Of course
we should pass the geometries as good as possible. But surfaces ARE a
problem. In my mind, the Pixar approach with user-programmable shading, is
 
a) Too complex to implement (yes I'm lazy)
b) Too complex to the average luser

Also, if the shading is part of the interface, it is bound to lay some
constrains on what can and what cannot be done, thus limiting creativity.
 
As I see it, the difference between most PD tracers is not what geometries
they eat (even if they eat NFF, OFF, DXF, RTK, XYZ, HIC, ETC) but how they
shade them. Some use 3d textures, some use 2d bitmapps, some use wavesources
and other use other things. Some use projective mapping, some use parameters
on the surfaces for mapping, and some has texturemap coordinates stored in
each vertex...
 
This is a problem to standardize, and is why I cant support renderman in 
my renderer. Where do I put the texturemap coordinates 'per vertex' in
a sphere :-)

Also, to MY warped mind, all these differences are the strengths and
weaknesses of the renderers! If we standardize these, why write more than
one renderer in the first place (and take all the fun out of it) :-( ?
 
I'm not saying standards is a Bad Thing. I'm not saying Renderman is a
Bad Thing. I'm just saying that they might somehow kick creativity, an
d they may take an awful lot of time, if they are too complex.

Like I said in an earlier post: Let's define RayMond interface as:

* Renderman primitives
* All features of renderman with things impossible in raytracing
  (e.g. true displacement shading) ripped out
* Effichiency shemes thrown in
* Editable objects (move, squach, fiddle)
* Not nessecarily having standardized shading
 
When a raymond surface wants to be wood, it should say so, and spit out
the settings for 'wood' as it was defined in the renderer/modeller
creating that file. However, if the other renderer is different, it
only cares about those parts of the shading it can understand, such as
ambient light, surface color e.t.c. and tells the user: Hey user,
this is supposed to be wood, want to alster something to make it look
more like that? 

And the user can.
 
Sorry for being incmprhnsibl, I'm under timestrain (bus in 1 minute ;-)
and a stupid keyboard.

CU all!



-- 
* * * * * * * * * * * * * * * * *          (This rent for space)
* My signature is smaller than  * Be warned! The letter 'Z' is Copyright 1991
* yours!  - zap@lysator.liu.se  * by Zap Inc. So are the colors Red, Green and
* * * * * * * * * * * * * * * * * Greenish-yellow (Blue was taken by IBM) 
--
* * * * * * * * * * * * * * * * *          (This rent for space)
* My signature is smaller than  * Be warned! The letter 'Z' is Copyright 1991
* yours!  - zap@lysator.liu.se  * by Zap Inc. So are the colors Red, Green and
* * * * * * * * * * * * * * * * * Greenish-yellow (Blue was taken by IBM)