protocol: add Presentation feedback flags

Graphics / Wayland / Weston - Pekka Paalanen [collabora.co.uk] - 20 January 2015 19:12 UTC

Add the missing feedback flags to the Presentation extension protocol specification.

These flags are slightly different from the previous RFCv3.1 definition: http://lists.freedesktop.org/archives/wayland-devel/2014-March/013598.html

Now, all compositors are safe to use 0 as the flags if they don't bother setting them properly. 0 is the "worst case" with the least guarantees.

The meaning of ZERO_COPY is not exactly the opposite of the old COPY flag. ZERO_COPY is more strict, but applies only to that one surface. Therefore it can be used to verify a zero-copy video playback pipeline, also to a hardware overlay.

There is no longer a flag to clearly indicate if the final presentation was done by a copy or a page flip. ZERO_COPY forbids the copy, but VSYNC alone does allow copy in case it cannot tear. It is possible to have first a compositing pass, and then another copy into the frontbuffer, and still set VSYNC if it cannot tear. Usually "cannot tear" is too hard to guarantee with a copy, so it often implies a page flip.

0de22a3 protocol: add Presentation feedback flags
protocol/presentation_timing.xml | 42 +++++++++++++++++++++++++++++++++++---
1 file changed, 39 insertions(+), 3 deletions(-)

Upstream: cgit.freedesktop.org

  • Share