Re: [PyOpenGL-Users] How to use shaders in pyopengl

[Don L. <go...@gm...>]

I'm having a similar problem with shaders in Windows.

I have a WxPython/PyOpenGL app that uses shaders and works fine in
Ubuntu 8.10, but when I try to run it in Windows XP, I get this error:

  File "c:\program
files\python\lib\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
glCreateProgram, check for bool(glCreateProgram) before calling

If I understand correctly, this is because OpenGL for Windows is stuck
at version 1.1 and needs extensions to use shaders. I'm not exactly
clear on how to use extensions, but judging from your
OpenGL/tests/tests.py file, all you have to do is import the proper
extension. I also found this snippet on your blog and in a tutorial:

from OpenGL.GL import *
from OpenGL.GL.ARB.shader_objects import *
from OpenGL.GL.ARB.fragment_shader import *
from OpenGL.GL.ARB.vertex_shader import *
from OpenGL.extensions import alternate
glCreateShader = alternate( 'glCreateShader', glCreateShader,
glCreateShaderObjectARB )
glShaderSource = alternate( 'glShaderSource', glShaderSource, glShaderSourceARB)
glCompileShader = alternate( 'glCompileShader', glCompileShader,
glCompileShaderARB)
glCreateProgram = alternate( 'glCreateProgram', glCreateProgram,
glCreateProgramObjectARB)
glAttachShader = alternate( 'glAttachShader', glAttachShader,glAttachObjectARB )
glValidateProgram = alternate(
'glValidateProgram',glValidateProgram,glValidateProgramARB )
glLinkProgram = alternate( 'glLinkProgram',glLinkProgram,glLinkProgramARB )
glDeleteShader = alternate( 'glDeleteShader', glDeleteShader,glDeleteObjectARB )
glUseProgram = alternate('glUseProgram',glUseProgram,glUseProgramObjectARB )

But adding this doesn't help. I just get this error instead:

  File "c:\program
files\python\lib\site-packages\PyOpenGL-3.0.0b6-py2.5.egg\OpenGL\extensions.py",
line 65, in __call__
    self.__name__,
OpenGL.error.NullFunctionError: Attempt to call an undefined alterate
function (glCreateProgram, glCreateProgramObjectARB), check for
bool(glCreateProgram) before calling

Do I need to do something first to make the extensions available to
use? To see which extensions are available, I added the following line
to my program just before the glCreateProgram call:

print "\n".join(glGetString(GL_EXTENSIONS).split(' '))

And this is what it says:

GL_WIN_swap_hint
GL_EXT_bgra
GL_EXT_paletted_texture

Do I need to use glewpy or something to get access to the shader
extensions in Windows? I've confirmed that OpenGL shader extensions
work on this computer with OpenGL Extensions Viewer. I've also tried
the release version of PyOpenGL 3.0.0b6 as well as the CVS head
version (but not the bzr version). I'm stumped... The OpenGL red book
states that "OpenGL 1.2 introduces the first ARB-approved extensions."
Is that relevant, considering OpenGL is 1.1 in Windows?

I've attached my program. The OpenGL code is in fft/map/viewer.py. Any
help would be appreciated.

Thanks,
-gomtuu