Re: [PyOpenGL-Users] Shader problems

[Tim B. <tim...@gm...>]

Mike-
Thanks for your comprehensive response!  I've managed to figure out that I
need to use the ARB extensions but that they do work (downloaded a c example
program that convinced myself of this).  Now I gotta figure out whether
there's an ARB-supporting computer I can demo to my instructor with, if not
it doesn't look too bad to support both with a runtime switch ;)

Thanks again!
-Tim

On Sun, Nov 16, 2008 at 11:07 AM, Mike C. Fletcher
<mcf...@vr...>wrote:

> Tim Bocek wrote:
>
>> Using Kubuntu Intrepid (8.10), PyOpenGL 3.0b6, proprietary nvidia
>> drivers (though I'm not sure what specific card is in this computer).
>> I am trying to get shaders to work using PyOpenGL, but calling
>>
>> glCreateShader(GL_FRAGMENT_SHADER) produces the exception:
>>
>> Traceback (most recent call last):
>>  File "./main.py", line 154, in <module>
>>    testShader = shader.FragmentShader("testShader.glsl")
>>  File "/home/rya/hw3/shader.py", line 11, in __init__
>>    self.__shader = glCreateShader(GL_FRAGMENT_SHADER)
>>  File
>> "/usr/lib/python2.5/site-packages/PyOpenGL-3.0.0b6-py2.5.egg/OpenGL/platform/baseplatform.py",
>> line 280, in __call__
>>    self.__name__, self.__name__,
>> OpenGL.error.NullFunctionError: Attempt to call an undefined function
>> glCreateShader, check for bool(glCreateShader) before calling
>>
>> Does this mean that my video card and/or opengl install does not
>> support shaders?  If that's not what this means, then what could be
>> going on?
>>
>>
> The possibilities are (there are probably other ones, but these are what
> comes to mind immediately):
>
>   * Your card does not support shaders
>         o possible for fairly old/low-level hardware
>   * Your card only supports shaders with the ARB extension
>     (glCreateShaderARB)
>         o common for slightly older hardware or drivers
>   * Your card only supports lower-level "program" shaders (pre-GLSL)
>         o common for older integrated graphics solutions
>   * Your card is currently running in non-accelerated mode
>         o e.g. because of a kernel mismatch versus the X driver
>   * You are calling the shader creation before you have an active
>     OpenGL context
>         o many implementations require a valid GL context before they
>           let you create shaders and the like
>   * You are calling the code on a software-only context
>         o e.g. because of requesting a context which can't be hardware
>           accelerated
>
> To debug these kinds of things:
>
>   * lspci | grep nVidia | grep VGA
>         o should tell you your card name, you can then google to see
>           what features the card supports
>   * glxinfo | grep -ir version
>         o should tell you whether your drivers support GL version
>           2.0.0 or greater
>   * add glGetString( GL_VERSION ) and print the result in your code
>         o if > 2.0.0 you should have glCreateShader available
>   * add glGetString( GL_EXTENSIONS ) and print the result in your code
>         o if GL_ARB_shader_objects is in the list, then you need to
>           use the ARB form of the functionality
>   * import OpenGL.GL.ARB.shader_objects and check for bool(
>     glCreateShaderObjectARB )
>         o when it's true, you can use it...
>   * try different (known-to-work) code for initializing the context to
>     be sure you get a shader-friendly context
>
> HTH,
> Mike
>
> --
> ________________________________________________
>  Mike C. Fletcher
>  Designer, VR Plumber, Coder
>  http://www.vrplumber.com
>  http://blog.vrplumber.com
>
>