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.
Plus, if there is draw->width and back->width, I guess they can be
different size, thus switching may be incorrect relative to buffer
size too.
Fake front and back are resized at the same time with dri3 AFAICT.
This means that with respect to dimensions, the new code should be
equivalent to the old one.
I don't remember the code enough to remember if and why the sizes can be
different.
Thanks,
Thomas
Yours,
Axel Davy
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