macOS: Implement support for backing store static contents

We already had the machinery to copy one buffer to another, so this
machinery has been generalized a bit, so we can use it to preserve
the static content during buffer resize.

As explained in the comments, we need to do the buffer copies during
buffer creation, instead of relying on our back buffer finalization,
as we are not guaranteed that we can always copy the static content
from the front buffer.

Pick-to: 6.7
Change-Id: Ia9b3ac6ec982949990d172b0b14f35b13bbae92a
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

1 files changed, 5 insertions, 0 deletions

diff --git a/tests/auto/gui/kernel/qbackingstore/tst_qbackingstore.cpp b/tests/auto/gui/kernel/qbackingstore/tst_qbackingstore.cpp
index 8a3d61829a..a830d14be8 100644
--- a/tests/auto/gui/kernel/qbackingstore/tst_qbackingstore.cpp
+++ b/tests/auto/gui/kernel/qbackingstore/tst_qbackingstore.cpp
@@ -93,6 +93,11 @@ void tst_QBackingStore::paint()
     QRect rect(0, 0, 100, 100);
     backingStore.resize(rect.size());
 
+    // Partial fill of a fresh backingstore should not crash
+    backingStore.beginPaint(QRect(0, 0, 50, 50));
+    backingStore.endPaint();
+    backingStore.flush(rect);
+
     // Two rounds, with flush in between
     for (int i = 0; i < 2; ++i) {
         backingStore.beginPaint(rect);