[PyOpenGL-Users] glutSetWindow in a thread segfaults

[U. T. <afr...@go...>]

Hi people,

We are working on a small program using pyode and pyopengl to simulate
a very simple robot. Nearly all the modelling is finished, and the
last thing left is a virtual camera that takes a snapshot of the field
of view of the robot. A class called display handles visualization and
the virtual camera. This class is in a thread of its own. Our program
has two windows; one displays the complete simulation environment, the
other displays the viewpoint of the camera. In order to save what is
in the camera window as an image, we do the following:

def capture(self, path):
        self.draw_lock.acquire()
        glutSetWindow(self.subwindow)
        glPixelStorei(GL_PACK_ALIGNMENT, 1)
        data = glReadPixelsub(0, 0, self.subwindow_width,
self.subwindow_height, GL_RGB)
	image = Image.fromstring( 'RGB',
(int(self.subwindow_width),int(self.subwindow_height)), data )
	image = image.transpose( Image.FLIP_TOP_BOTTOM)
        image.save(path)
        self.draw_lock.release()
        return True

The Image object is from PIL. As you can see, thread locks are
necessary to stop the display functions from changing the displays;
otherwise, an OpenGL error is thrown.

When this routine is called from the display class of which it is a
member, there are no errors; the image is saved in the given path.
When it is called from outside the thread, however, glutSetWindow
causes a segmentation fault. This happens not each and every time but
most of the time, which puzzled me even more. Before we put in locks
for the drawing functions, segfaults and OpenGL errors would each
happen.

I am suspecting that there is another resource which has to be locked,
but no idea what and how. Any ideas what the reason might be, or how
to find a workaround?

Cheers,
Ulas