Fix QHighDpi::fromNativeLocalExposedRegion rounding errors

Ceiling width/height fails to take into account rects that do no have
their top left position on an exact point boundary.

Example: QRect(0,0 20x20) and QRect(1,1 20x20) with scale 2.0 would give
the same result of QRect(0,0 10x10). The correct rects are QRect(0,0 10x10)
and QRect(0,0 11x11), so that we are sure to repaint all pixels within the
exposed region.

Before 5138fada0b9c, rects were also rounded incorrectly. The old method
would give the result of QRect(0,0 11x11) in both cases, causing the
exposed region to be larger than a window.

Amends 5138fada0b9ce3968b23ec11df5f0d4e67544c43

Task-number: QTBUG-63943
Change-Id: I9f3dddf649bdc506c23bce1b6704860d61481459
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/gui/kernel/qhighdpiscaling_p.h b/src/gui/kernel/qhighdpiscaling_p.h
index 0a060a2d2c..83fc9452c5 100644
--- a/src/gui/kernel/qhighdpiscaling_p.h
+++ b/src/gui/kernel/qhighdpiscaling_p.h
@@ -402,7 +402,8 @@ inline QRegion fromNativeLocalExposedRegion(const QRegion &pixelRegion, const QW
         const QPointF topLeftP = rect.topLeft() / scaleFactor;
         const QSizeF sizeP = rect.size() / scaleFactor;
         pointRegion += QRect(QPoint(qFloor(topLeftP.x()), qFloor(topLeftP.y())),
-                             QSize(qCeil(sizeP.width()), qCeil(sizeP.height())));
+                             QPoint(qCeil(topLeftP.x() + sizeP.width()  - 1.0),
+                                    qCeil(topLeftP.y() + sizeP.height() - 1.0)));
     }
     return pointRegion;
 }