pyopengl-users

[PyOpenGL-Users] Shader Function Problems

[Ian M. <geo...@gm...>]

Hi,

I finally got some sort of error checking working for ATI cards.  The errors
are weird.  glGetShaderInfoLog(...) for each part of the program spits out:

Vertex shader was successfully compiled to run on hardware.
Fragment shader was successfully compiled to run on hardware.

But strangely, glGetInfoLogARB(...) spits out:

Fragment shader(s) failed to link,  vertex shader(s) linked.
Fragment Shader not supported by HW

Needless to say, it crashes later on glUseProgramObjectARB(...) with
an 'invalid operation'.  These problems occur when certain functions
are called in my program.  Here's a function that causes such an
error:

float diffuse_coefficient(int lightnum) {
    vec3 l = normalize(gl_LightSource[lightnum].position.xyz-vVertex);
    return max(dot(normal,l),0.0);
}

My ideas:
vVertex is a varying vec3.  Could this be the problem?
is max(dot(normal,l),0.0) too much for one line?  I saw something about ALU
limits.  I don't know if this qualifies.

Any other ideas?  What's going on here?  How can I make this work?

Ian

Re: [PyOpenGL-Users] Shader Function Problems

[Mike C. F. <mcf...@vr...>]

Ian Mallett wrote:
...
> But strangely, glGetInfoLogARB(...) spits out:
>
>
>
> Fragment shader(s) failed to link,  vertex shader(s) linked. 
> Fragment Shader not supported by HW
>
> Needless to say, it crashes later on glUseProgramObjectARB(...) with an 'invalid operation'.
Yeah, saw the same with my ATI Radeon 3650, I wound up using both 
glGetInfoLog and glGetProgramInfoLog and found that with both I'd 
normally get some description of a failure, but that the shaders would 
pass validation (i.e. the first programmatic indication of the error was 
on the invalid operation error).  For OpenGLContext's shader support I 
wound up doing a try:except around the glUseProgram call and if there's 
a GL error raised I print all of the logs for all of the linked 
components as well as the program's logs.
>   These problems occur when certain functions are called in my program.  Here's a function that causes such an error:
>
>
>   
> float diffuse_coefficient(int lightnum) {
>     vec3 l = normalize(gl_LightSource[lightnum].position.xyz-vVertex);
>     return max(dot(normal,l),0.0);
> }
>
> My ideas:
> vVertex is a varying vec3.  Could this be the problem?
Doesn't look like a problem to me, I seem to recall using varying 
vectors in such ways many times.
> is max(dot(normal,l),0.0) too much for one line?  I saw something 
> about ALU limits.  I don't know if this qualifies. 
I'd be surprised if that went over any limit, I've certainly written 
more complex calculations.

Sorry I don't have more help to offer here.  Might want to check that 
lightnum is the proper value?  Also, stupid question, where'd you get 
"normal" there?  I don't see it in my handy GLSL quickref.  Is it from 
some outer scope (or an attribute/uniform)?

HTH,
Mike

-- 
________________________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://www.vrplumber.com
  http://blog.vrplumber.com

Re: [PyOpenGL-Users] Shader Function Problems

[Ian M. <geo...@gm...>]

Yea, normal is custom defined.

I'm working on a fix which works, I think.  The problem was with sending
variable ints to gl_LightSource[n].