[GEM-dev] Problem with glitching on OS X at high frame rates

Theo Burt tb504 at york.ac.uk
Thu Jul 19 15:22:30 CEST 2012

Chris and Cyrille, thank you both for this very useful information and 
ideas for testing etc. I will investigate some more and post results 
when I get some.

Thanks to all

On 19/07/2012 13:49, chris clepper wrote:
> On Thu, Jul 19, 2012 at 6:14 AM, Theo Burt <tb504 at york.ac.uk 
> <mailto:tb504 at york.ac.uk>> wrote:
>     Does anyone know how the vsync works on OSX? I mean how does GEM
>     wait for the vsync, to flip the buffer? Does it block the process
>     at any point? Is the process blocked by any part of GEM at any
>     point, on a per frame basis?
> VBL sync is a single line of code that turns it on/off.  GEM's render 
> engine doesn't do anything different based on that state.
>     For example, after the all the opengl has been executed, I'm
>     presuming a system call is made to actually render the screen?
>     What is this call, and could it simply be that something, perhaps
>     operating system related, is causing it to take too long to
>     return? That would tie in with moving windows around the desktop
>     making the problem worse...
> The last call in any GL chain is glFinish() which flushes all of the 
> commands to the card via the driver.  The driver can block the 
> uploading of commands to the card for various reasons most of which 
> are not documented anywhere.  Apple has OpenGL profiling tools that 
> can show where time is being spent in the driver.

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