HiDPI: Fix calculating window mask from pixmap on drag and drop

Use platform window directly for setting a mask to prevent bitmap
scaling if pixmap and window DPR are the same.

Amends: 42f788ffe26d67864d569c3a3044619d49fc693a

Task-number: QTBUG-61948
Change-Id: I5eec85c01f20bdefff7343e83ff10cbcb2c79508
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/gui/kernel/qshapedpixmapdndwindow.cpp b/src/gui/kernel/qshapedpixmapdndwindow.cpp
index b54c6b67a2..8509eb0961 100644
--- a/src/gui/kernel/qshapedpixmapdndwindow.cpp
+++ b/src/gui/kernel/qshapedpixmapdndwindow.cpp
@@ -39,6 +39,8 @@
 
 #include "qshapedpixmapdndwindow_p.h"
 
+#include "qplatformwindow.h"
+
 #include <QtGui/QPainter>
 #include <QtGui/QCursor>
 #include <QtGui/QGuiApplication>
@@ -70,7 +72,12 @@ void QShapedPixmapWindow::setPixmap(const QPixmap &pixmap)
         if (!mask.isNull()) {
             if (!handle())
                 create();
-            setMask(mask);
+            if (auto platformWindow = handle()) {
+                const auto pixmapDpr = m_pixmap.devicePixelRatio();
+                const auto winDpr = devicePixelRatio();
+                const auto maskSize = (QSizeF(m_pixmap.size()) * winDpr / pixmapDpr).toSize();
+                platformWindow->setMask(QBitmap(mask.scaled(maskSize)));
+            }
         }
     }
 }