[PyOpenGL-Users] glPixelStorei causes glReadPixelsub Segmentation Fault (PyOpenGL 3.0.0b1)

[U. A. E. <ar...@cd...>]

I am receiving this error after upgrading my project to use PyOpenGL
3.0.0b1 (the same code works in version 2.0.2.01):

########################################
Traceback (most recent call last):
  File "C:\Python25\Lib\site-packages\wx-2.8-msw-unicode\wx\_core.py",
line 14099, in <lambda>
    lambda event: event.callable(*event.args, **event.kw) )
  File
"C:\bicspe\construct\python\src\cdr\cellsim\clients\gui\OpenGLRenderer.py",
line 933, in EventUpdate
    tr.endTile()
  File
"C:\bicspe\construct\python\src\cdr\cellsim\clients\gui\TileRenderer.py",
line 118, in endTile
    data = array(GL.glReadPixelsub(0, 0, width, height, GL.GL_RGB))
  File
"C:\Python25\lib\site-packages\pyopengl-3.0.0b1-py2.5.egg\OpenGL\GL\images.py",
line 233, in glReadPixels
    ctypes.c_void_p( imageData )
WindowsError: exception: access violation writing 0x00000000
#########################################

Of course, the error shown occurs on windows xp... however, it
segmentation faults on Mac OSX and Fedora 8 in the same location. 
Basically, I am doing a large opengl capture using tile rendering.  Here
is my class function where the error occurs:

<div>
#########################################
    def endTile(self):
        GL.glFlush()

        prevRowLength = GL.glGetIntegerv(GL.GL_PACK_ROW_LENGTH)
        prevSkipRows = GL.glGetIntegerv(GL.GL_PACK_SKIP_ROWS)
        prevSkipPixels = GL.glGetIntegerv(GL.GL_PACK_SKIP_PIXELS)

        destX = self.tileWidth * self.currentColumn
        destY = self.tileHeight * self.currentRow

        GL.glPixelStorei(GL.GL_PACK_ROW_LENGTH, int(self.imageWidth))
        GL.glPixelStorei(GL.GL_PACK_SKIP_ROWS, int(destY))
        GL.glPixelStorei(GL.GL_PACK_SKIP_PIXELS, int(destX))

        width = self.tileWidth
        height = self.tileHeight
        #grab only the pixels we need on the edges
        if self.currentRow == self.rows - 1 and self.tileHeightEdge:
            height = self.tileHeightEdge
        if self.currentColumn == self.columns - 1 and self.tileWidthEdge:
            width = self.tileWidthEdge

        data = array(GL.glReadPixelsub(0, 0, width, height, GL.GL_RGB))

        GL.glPixelStorei(GL.GL_PACK_ROW_LENGTH, int(prevRowLength))
        GL.glPixelStorei(GL.GL_PACK_SKIP_ROWS, int(prevSkipRows))
        GL.glPixelStorei(GL.GL_PACK_SKIP_PIXELS, int(prevSkipPixels))

        self.currentTile += 1

        if self.currentTile > self.rows * self.columns:
            GL.glViewport(self.viewportSave[0], self.viewportSave[1], self.viewportSave[2], self.viewportSave[3])
            self.currentTile = -1
        else:
            GL.glPixelStorei(GL.GL_PACK_ALIGNMENT, 1)
            image = Image.fromstring("RGB", (width, height), data.tostring())
            self.image.paste(image, (destX, destY))
#########################################
</div>

If I comment out all the GL.glPixelStorei(GL.GL_PACK_ROW_LENGTH, ...),
GL.glPixelStorei(GL.GL_PACK_SKIP_ROWS, ...), and
GL.glPixelStorei(GL.GL_PACK_SKIP_PIXELS, ...) calls, the error DISAPPEARS
on all platforms mentioned above; however, the end result that I seek is
not right.

Is this a known bug or does anyone have a workaround?

Thanks,
U. Artie Eoff