glReadPixels with null pointer

Hi all,

I had problems when using glReadPixels when the data buffer pointer 
passed to the function is zero:

glReadPixels(0, 0, capSize[0], capSize[1], GL_BGRA, GL_UNSIGNED_BYTE, 0)

I was doing this while reading from a pixel buffer object. This caused a 
segmentation fault in OpenGL/GL/images.py when simple.glReadPixels is 
called. I found a way to fix this by setting the variable to ensure it 
is a "None" pointer.

         if array is None:
             array = images.SetupPixelRead( format, (width,height), type )
         else:
             if array != 0:
                 array = arrayType.asArray( array )
             else:
                 array = arrayType.asArray( None )
         imageData = arrayType.voidDataPointer( array )
         simple.glReadPixels(
             x,y,
             width, height,
             format,type,
             imageData

This branch fixes the segfault problem: 
https://code.launchpad.net/~thetourist/pyopengl/tim

Regards,

Tim Sheerman-Chase


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