When a GLKView is resized, there are some behind-the-scenes operations that take place on the buffers and context of that GLKView. During the time it takes to perform these behind-the-scenes operations, drawing to the GLKView does not produce correct results.
In my scenario, I have a GLKView that has setNeedsDisplay enabled, so that anytime I need to update it's contents on screen, I just call -setNeedsDisplay on that
GLKView. I'm using GLKView to draw images, so if I need to draw an image with a different size, I need to also change the size of the GLKView.
The problem: When I change the size of the GLKView and call setNeedsDisplay on that view, the result on screen is not correct. This is because the GLKView is not done finishing the behind-the-scenes operations invoked by the new size change before it tries to draw the new image.
I found a work-around to this by calling: performSelector:@selector(setNeedsDisplay) withObject:nil afterDelay:0 instead of just setNeedsDisplay on the GLKView. This basically forces the main thread to wait for all the behind-the-scenes openGL operations to be completed before calling setNeedsDisplay. Although this works ok, I am wondering if there is a better solution. For example, is there an openGL call to make the thread wait for all openGL operations to be completed before continuing?
The solution was to reset the CIContext object after the GLKView has been resized.