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

[chris clepper]

On Thu, Jul 19, 2012 at 6:14 AM, Theo Burt <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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