QMacStyle: Make helper-NSViews layer-backed

This prevents the view from triggering display of its superview when
being temporarily added, which is both inefficient and causes issues
when those dirty-rects are wrong due to the wrong frame position of
the added view.

The additional drawRect: calls and corresponding expose events
resulting from the needsDisplay calls also caused repaint issues
in Qt Widgets. QWidgetBackingStore doesn't seem to take the exposed
region into account for an expose event, and will try to flush all
dirty regions. Some of those may be outside the exposed region,
and will be clipped away by the window system, never ending up on
the screen, but with Widgets still thinking it has flushed all
dirty regions.

This is a separate issue, possibly solvable by setting the
wantsDefaultClipping property on NSView to NO, but this needs
further testing, so applying this commit as workaround makes
sense, even if it's just hiding the real bug.

Task-number: QTBUG-67998
Task-number: QTBUG-68023
Task-number: QTBUG-69990
Task-number: QTBUG-69740
Task-number: QTBUG-69292
Task-number: QTBUG-69332
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
(cherry picked from commit 38979332d0a66666ebd178bccd7e7a2b300a7e42)
Change-Id: I4ef3fef29f749daa4f3a11fe9186ae77b359f966
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

0 files changed, 0 insertions, 0 deletions