title: glFlush() takes very long time on window with transparent background
body: <p>I used the code from <a href="https://stackoverflow.com/questions/4052940/win32-how-to-make-an-opengl-rendering-context-with-transparent-background">How to make an OpenGL rendering context with transparent background?</a> to create a window with transparent background. My problem is that the frame rate is very low - I have around 20 frames/sec even when I draw one quad(made from 2 triangles). I tried to find out why and glFlush() takes around 0.047 seconds. Do you have any idea why? Same thing is rendered in a window that does not have transparent background at 6000 fps(when I remove 60 fps limitation). It also takes one core to 100%. I test it on a Q9450@2.66GHz with ATI Radeon 4800 using Win7.</p>