[PyOpenGL-Devel] Bug found in glReadPixels

[Geert H. V. <gee...@gm...>]

Hey guys,

Just wanted to report a bug I found in glReadPixels which has caused
me major annoyance yesterday.

glReadPixels returns a numpy array with a specific datatype. I found
out that the shape parameter given to this array has the rows and
columns switched. This will not be a problem for most users, as the
flattened array will be interpreted correctly. If one however does
some operations on it, like transposes or left right swapping, this
results in a corrupted image. For me there was an easy workaround by
using:

data = data.reshape((data.shape[1],data.shape[0]))

However, it would be nice if this was fixed in future versions.

It can be fixed in multiple points of the source code, like this line
in OpenGL/GL/images.py:

array = imageData = images.SetupPixelRead( format, (width,height), type )

Only width and height need to be swapped for it to work.

I tested this on both a windows and a linux distribution but would
like someone else to test it as well to rule out any stupidity. I
believe the cause of the bug is the way OpenGL presents the array data
is not consistent with the standard way numpy expects it.

Kind regards,
Geert Henk Visser