Fix data race with dirty flags set from property change events

Ensure that dirty flags (typically on buffers and textures) are set
as the very first thing we do in a frame by processing changes sent
from the frontend to the backend before scheduling any jobs.

Without this change, the dirty flag was sometimes being set whilst the
renderer submission thread was busy processing the RenderViews and
RenderCommands. This could result in the submission thread seeing the
dirty flag on a buffer and performing a glBufferData() call before the
jobs to populate the new data had been executed and then clearing the
dirty flag.

Depending upon the exact timings, updates appeared to lag a change
behind or just get missed entirely.

Later, when we have aspects that perform changes that need to be sent
to the frontend, it might be a good idea to add a set of flags to the
QChangeArbiter->syncChanges() call that allows to process events:

* From frontend to backend only (at start of frame)
* From backend to frontend only (at end of frame or other well defined
  times)
* From backend to backend (to allow aspects to sync with each other)

Task-Id: QTBUG-49602
Task-Id: QTBUG-49599
Change-Id: I5b2d4d6d81b119c8ec921ba4f8b90e3703c251da
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

0 files changed, 0 insertions, 0 deletions