macOS: Optionally flush sub-layers via sub-image copies of the backingstore

When we're flushing the backingstore to sub-views with their own layers
we don't want to pay the cost of uploading the whole backingstore to the
GPU in the case where we're dealing with a discrete GPU.

To work around this we make a copy of the appropriate part of the surfcace.

This results in additional copies of the data, and will need further
investigation to limit these.

Task-number: QTBUG-77447
Change-Id: I318ae80e433dd7b0a55fd5a598b19f114d8bd28e
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
(cherry picked from commit eaf4911db29a82b3d94826a8ff09afe075a2b636)
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

0 files changed, 0 insertions, 0 deletions