Q: What’s the difference between glFlush() and glFinish()?
A: OpenGL commands are not executed immediately. Instead, they are submitted to a command buffer that is then fed into to the hardware. The glFlush() and glFinish() commands are both used to force submission of the command buffer to the hardware for execution. glFlush() causes all OpenGL commands currently queued to be submitted to the hardware for execution. This function returns immediately after having transferred the pending OpenGL command queue to the hardware (or software) renderer. These commands are queued for execution in some finite amount of time, but glFlush() does not block waiting for command completion.