On 06/28/2017 08:48 PM, Axel Davy wrote:
On 28/06/2017 20:40, Thomas Hellstrom wrote:
On 06/28/2017 07:36 PM, Axel Davy wrote:
Hi,
To my knowledge, this is invalid to switch the front fake buffer
with the back buffer.
The front buffer is supposed to take into account what the app draws
with the xserver commands, etc.
SwapBuffers should bring the contents of the back buffer to the front
(and fake front if applicable) buffer, and the backbuffer contents
become undefined, or tagged with a certain age. None of this is
violated here. The old back buffer will become the new fake front and
appropriately synced with X rendering as needed.
Is there a specific scenario you are concerned with?
When I investigated the use of front buffer when writing the patch to
add secondary gpu support, I understood almost all apps don't use
front buffer at all, but when they do, it's to interact with the real
content displayed to the user, which can see some modifications.
So this behaviour doesn't change with the patch. As soon as the old back
buffer is swapped in place as the new fake front, it starts
synchronizing with the X rendered content when needed. Specifically that
happens during glXWaitGL and glXWaitX.
/Thomas
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