Re: [PyOpenGL-Users] glVertexAttribPointer(); loading platform-specific functions

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

Joshua Davis wrote:
...
> Update: I've run the same program on a friend's computer, which is  
> GeForce 8600M GT (OpenGL 3.0), Mac OX 10.5.8, Python 2.5.1, Numpy  
> 1.3.0, PyOpenGL 3.0.1a3. The program works perfectly (whereas on my  
> machine, a Radeon 9600, it produces no fragments). The debugging  
> output is listed below. One thing I notice is that  
> glVertexAttribPointer() is used on my friend's computer, whereas  
> glVertexAttribPointerARB() is used on mine.
>   
Right, your machine doesn't provide OpenGL 2.x, theirs does.  The
extension *should* work if it is present, and as noted, when I use the
ARB versions of the entry points here, the code still produces fragments.
> I think that even a Radeon 9600 is capable of using vertex attribute  
> arrays, but if supporting hardware this old is not worth your time,  
> then let me know; I can take it.
>   
AFAICS the code is producing the correct calls to OpenGL to produce the
results.  Possibilities still open:

    * hardware doesn't "really" support shader attributes (or supports
      them with quirks/extra requirements)
    * the PyOpenGL OpenGL.GL.shaders module may have a bug in how it
      maps calls into ARB (but not into core), where the more modern
      implementations are able to handle the "off" mapping, but not the
      older implementations
          o may be some setup missing that older implementation requires?
          o may be some call that's not raising errors, but doesn't
            match required usage on 9600 implementation?
    * ??

we're probably to the point now where the paths to try to fix it would be:

    * ask on an OpenGL experts forum about what the code should do to
      get attributes working on 9600s
    * find some old (C) OpenGL code that worked with a 9600 and shader
      attributes, ATI's developer site might have something of this
      vintage kicking around.  Comparing against what we're doing may
      show something missing/wrong for the older hardware.

You might have luck in either of those directions.  I'm hesitant to
explore them without having hardware on which to test hypotheses, but if
you find something I can certainly try to help with it.

HTH,
Mike

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