[osg-users] Measure Render-Time prior to SwapBuffers with Multhreaded Rendering

[Philipp Meyer]

Hi,

I'm trying to measure the render time of my application. The render time is defined as the time between the start of a new frame (begin of frame loop) and the time where all operations on CPU and GPU for that frame have finished. 

However, I want to exclude swapBuffers from the measurement because I can not turn off VSYNC on my test system and swapBuffers will block until the VSYNC signal arrives, invalidating my measurements.

I have already successfully implemented this measurement by using a custom SwapCallback and attaching it to my graphicsContext. Within the SwapCallback, I first issue a call to glFinish() to make sure all GPU operations are finished, then measure the time and then call swapBuffers afterwards.

This works fine as long as the threading mode of the viewer is set to singleThreaded. However, I'm using multiple cameras viewing the same scene from different angles, so for maximum performance I've set the threading mode to ThreadPerCamera. Now Im getting measurements that no longer make sense (the duration is way too short), and I'm uncertain what actually causes this or how to fix it.

How do I best go about measuring this time?
In pseudocode, it would look smth like:

for(;;)
{
	tp1 = timepoint();
	//osg render scene multithreaded
	synchronizeWithOSGThreads();
	glFinish();
	tp2 = timepoint();
	renderTime = tp2 - tp1;
	swapBuffers();
}

Thank you!

Cheers,
Philipp

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http://forum.openscenegraph.org/viewtopic.php?p=69155#69155