Fix QHighDpi::fromNativeLocalExposedRegion rounding errors

Calling bottom/right/bottomRight on a QRect is discouraged, as it does
not give the true bottom-right corner of the rectangle, instead giving
a point one unit to the left and top of the true bottom right.

Dividing this point by a scale factor of e.g. 2, and then using qCeil
on the bottom right x and y coordinates would result in a pointRegion
that was 1x1 * scaleFactor larger than it should, manifesting as
rendering issues at later stages.

We can get away from the whole problem by initially converting the
QRect to a QRectF, and basing the pointRegion's rect on the scaled
size instead of bottom-right coordinates.

Change-Id: I4d4895660655cfa8749c93c7d2573ae79cd7898b
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/gui/kernel/qhighdpiscaling_p.h b/src/gui/kernel/qhighdpiscaling_p.h
index 32c8f07dc0..0a060a2d2c 100644
--- a/src/gui/kernel/qhighdpiscaling_p.h
+++ b/src/gui/kernel/qhighdpiscaling_p.h
@@ -398,11 +398,11 @@ inline QRegion fromNativeLocalExposedRegion(const QRegion &pixelRegion, const QW
 
     const qreal scaleFactor = QHighDpiScaling::factor(window);
     QRegion pointRegion;
-    for (const QRect &rect : pixelRegion) {
-        const QPointF topLeftP = QPointF(rect.topLeft()) / scaleFactor;
-        const QPointF bottomRightP = QPointF(rect.bottomRight()) / scaleFactor;
+    for (const QRectF &rect : pixelRegion) {
+        const QPointF topLeftP = rect.topLeft() / scaleFactor;
+        const QSizeF sizeP = rect.size() / scaleFactor;
         pointRegion += QRect(QPoint(qFloor(topLeftP.x()), qFloor(topLeftP.y())),
-                             QPoint(qCeil(bottomRightP.x()), qCeil(bottomRightP.y())));
+                             QSize(qCeil(sizeP.width()), qCeil(sizeP.height())));
     }
     return pointRegion;
 }