Geometry Shaders from Python

If you have tried to use geometry shaders using python's PyOpenGL you will have noticed that the show-stopper here is glProgramParameteri. Using this function results in:

OpenGL.error.NullFunctionError: Attempt to call an undefined function glProgramParameteri, check for bool(glProgramParameteri) before calling

Here is an implementation that will define it using ctypes:

#These three defines exist in OpenGL.GL, but does not correspond to those used here

GL_GEOMETRY_INPUT_TYPE_EXT = 0x8DDB

GL_GEOMETRY_OUTPUT_TYPE_EXT = 0x8DDC

GL_GEOMETRY_VERTICES_OUT_EXT = 0x8DDA

_glProgramParameteri = None

def glProgramParameteri( program, pname, value ):

global _glProgramParameteri

if not _glProgramParameteri:

import ctypes

# Open the opengl32.dll

gldll = ctypes.windll.opengl32

# define a function pointer prototype of *(GLuint program, GLenum pname, GLint value)

prototype = ctypes.WINFUNCTYPE( ctypes.c_int, ctypes.c_uint, ctypes.c_uint, ctypes.c_int )

# Get the win gl func adress

fptr = gldll.wglGetProcAddress( 'glProgramParameteriEXT' )

if fptr==0:

raise Exception( "wglGetProcAddress('glProgramParameteriEXT') returned a zero adress, which will result in a nullpointer error if used.")

_glProgramParameteri = prototype( fptr )

_glProgramParameteri( program, pname, value )

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