ingo wrote:

> What are programmable shaders?
> Can sombody try explain this to me in laymens terms, or point me to a page
> that does so. I did a (very) quick search this morning but found only stuff
> that needs at least a basic understanding of shaders. And that I do not
> have.

Basically, shaders are functions written in the RenderMan Shading
Language
(a language that on first inspection looks very similar to C) that
explicitly describe the interaction between light and some element of
the scene being rendered. For instance, there are surface shaders (which
return the color of light reflected from a point on a surface),
displacement shaders (which allow the surface of a solid to be modified
in some algorithmic manner, such as regularly-spaced dimples or bumps),
volume shaders (which modify the characteristic of light passing through
a volume of space, the interior of an object, et cetera), and others.
Their power comes from the fact that shaders allow the artist to
describe
*exactly* how the light interacts with a surface, how light is generated
by a light source (light source shaders), how a surface interacts with
reflected light (by calculating intensity, direction, color of reflected
light), and so forth. The interaction need not even be realistic; you
have
total freedom in your calculations.

There is a rather significant learning curve involved in using shaders.
I'd recommend "The RenderMan Companion" by Steve Upstill as a start.
It's ten years old, but it's still considered the classic beginner's
text on RenderMan, and it gives a good overall view about what shaders
do.

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Ken wrote:

> Ron Parker wrote:
> >
> > On Sat, 22 Jan 2000 19:13:16 -0800, Ken wrote:
> > >I really think I could give you, Samual, and Mick a run for your money
> > >if I set my mind to it but Gilles I couldn't touch if I tried.
> >
> > Ooh, that sounds like a challenge.  Like our own little IRTC. :)
>
> Sounds like fun. The topic will be "Printed Circuit Board Plating Facility".

What's all this? If that is the challenge, I've already lost!

--
Samuel Benge

E-Mail: STB### [at] aolcom

Visit the still unfinished isosurface tutorial: http://members.aol.com/stbenge

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"SamuelT." wrote:

> > Sounds like fun. The topic will be "Printed Circuit Board Plating Facility".
> 
> What's all this? If that is the challenge, I've already lost!

It was a joke son.

I picked a topic that I know that I am intimately familiar with and no
one else would be.  Gives me that winning edge.

If the topic were "A Scene Developed with only Matematical Constructs"
I would likewise be at a severe dissadvantage.

If the topic were "Poser figures in Pov" Gilles and Mick would have the
advantage because they own a copy of Poser and I don't.

-- 
Ken Tyler -  1300+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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Ken wrote:

> Sounds like fun. The topic will be "Printed Circuit Board Plating Facility".
>

Count me in. Look at what I did with printed circuit boards...
http://www.synaptic.ch/Greve/gtran/tran.htm
http://www.synaptic.ch/Greve/gtran/tran2.htm
(these pages need Flash)
These objects were made for a collective "installation" 2 years ago.
I didn't know these things were so hard to break and tear apart (got a few
blisters after that)...

G.

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Gilles Tran wrote:
> 
> Ken wrote:
> 
> > Sounds like fun. The topic will be "Printed Circuit Board Plating Facility".
> >
> 
> Count me in. Look at what I did with printed circuit boards...
> http://www.synaptic.ch/Greve/gtran/tran.htm
> http://www.synaptic.ch/Greve/gtran/tran2.htm
> (these pages need Flash)
> These objects were made for a collective "installation" 2 years ago.

They are different :)

> I didn't know these things were so hard to break and tear apart (got a few
> blisters after that)...

Tougher than most people would give them credit for. We use high
speed routers with tungsten carbide router bits to fabricate them
with.

-- 
Ken Tyler -  1300+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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I really liked those, I checked them out a while ago and thought "gee I
wouldn't mind a few of those around here"

--
Lance.
The Zone - http://come.to/the.zone
Gilles Tran <tra### [at] inapginrafr> wrote in message
news:388C433F.B3A73851@inapg.inra.fr...
>
> Ken wrote:
>
> > Sounds like fun. The topic will be "Printed Circuit Board Plating
Facility".
> >
>
> Count me in. Look at what I did with printed circuit boards...
> http://www.synaptic.ch/Greve/gtran/tran.htm
> http://www.synaptic.ch/Greve/gtran/tran2.htm
> (these pages need Flash)
> These objects were made for a collective "installation" 2 years ago.
> I didn't know these things were so hard to break and tear apart (got a few
> blisters after that)...
>
> G.
>

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Ken wrote:
> 
> Has this situation changed with the addition of UV mapping to MegaPov ?
> 
> I announced the existence of the POV-Ray Tag on the IRTC mailing list
> yesterday and within 2 hrs. got a request for programmable shaders :)
> 
> --

Sorry for late reply, but I was for a week on the mountains and off from
civilization (i.e. internet). 

I'm currently working with Shader patch, which is based on Mercier's
POVMAN patch. I wrote letter to  mr. Mercier and got his permission to
use his work as suitable. So far I got his initial version integrated
with MegaPov and some example shaders working. Currently I'm working
with shader compiler, for POVMAN version was rather limited.(this was
initially going rather slowly due to my inexperience with LEXX and YACC,
but now I've got grip). I try to add as much support for RM SL version
3.8 as possible: so far I've added support for vector and normal
keywords, support for mixing of variable declarations and statements).
After that I was able to compile wood shader from BMRT distribution and
its rendering even resembled wood ;-) 
My next task is adding support for user defined functions, as quite a
number of shaders use them. Then will come (???) matrixes and arrays.

One important thing is to add support for uv stuff, hopefully when I get
so far, someone will help me, as I don't have experience with it. 

Some of RM features will probably never be implemented, e.g. message
passing. My intention is to make easier creation of new patterns or
extending old ones, all this without source code compilation (e.g. it
would be quite easy to create slope dependent pattern with this patch).
If one is lucky, then it could be possible to use other features of RM
SL as well, but generally it ain't that easy. I guess that best would
be, if unimplemented features produce warning and will be eaten up by
shading compiler.

Well, I hope that all of you, who want shaders, do not get expectations
too high, as I don't have mucho tiempo for my patching (worst of all,
during new year holidays I managed to delete my files and had to start
from scratch). But I'm intended to work on it until it gives some
results or it is clear, that I'm not able to do it...

P.S. I'd like to see, that in this group (and other groups as well, save
p.o-t) messages are more on-topic.

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Ron Parker wrote:

> >After all, and if I understood well, renderman shaders must
> >be compiled with an ordinary C++ compiler, and they are -sort of-
> >dynamically linked to the renderer (who gives some data to
> >the shader, and get a pixel color or some other data in return).
> 
> Not exactly.  They're compiled into bytecode (IIRC) by the shader
> compiler, which is not really a C compiler.  They're then executed
> by the renderer pretty much as you say.
> 
Adjustment:
IIRC new version of BMRT shader compiler (2.5???) will compile shader
into C code, and RenderDotC  (another RM compliant scanline renderer)
compiles as well shader into C code, from which shared library (or dll)
is created.

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Oh, I forgot:
All my previous message was about surface (one can say pigment/texture)
shader. Is there interest in displacement shader? If there is, then I
would appreciate links/hints, how this should be implemented (in
unofficial.patches perhaps).

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Vahur Krouverk wrote:
> 
> Oh, I forgot:
> All my previous message was about surface (one can say pigment/texture)
> shader. Is there interest in displacement shader? If there is, then I
> would appreciate links/hints, how this should be implemented (in
> unofficial.patches perhaps).

I am glad to here that someone is working on it even if it is a basic
implementation. While you are working on it and you need advice I
suggest you take your questions to the povray.programming group. The
unofficial.patches group is more for when you actually have a working
model and you need feedback on it from people trying it out for you.
Right now you need programming specific issues resolved and .programming
is ideal for this purpose.

Cheers and good luck,

-- 
Ken Tyler -  1300+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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