When filling a pixmap after an assignment ensure the set DPR is not lost

Pick-to: 6.2 5.15
Change-Id: I649547ea277f9d074e6638e4b7b1206d3d3d976b
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

src/gui/image/qpixmap.cpp

@@ -899,6 +899,7 @@ void QPixmap::fill(const QColor &color)
         // it will be filled with new pixel data anyway.
         QPlatformPixmap *d = data->createCompatiblePlatformPixmap();
         d->resize(data->width(), data->height());
+        d->setDevicePixelRatio(data->devicePixelRatio());
         data = d;
     }
     data->fill(color);

tests/auto/gui/image/qpixmap/tst_qpixmap.cpp

@@ -121,6 +121,7 @@ private slots:
     void copy();
     void move();
     void deepCopyPreservesDpr();
+    void fillPreservesDpr();
     void dprPassthrough();
     void depthOfNullObjects();
 
@@ -1172,6 +1173,19 @@ void tst_QPixmap::deepCopyPreservesDpr()
     QCOMPARE(dest.devicePixelRatio(), dpr);
 }
 
+// Check that the DPR is preserved after doing a fill after an
+// assigned copy of the QPixmap
+void tst_QPixmap::fillPreservesDpr()
+{
+    const qreal dpr = 2;
+    QPixmap src(32, 32);
+    src.setDevicePixelRatio(dpr);
+    src.fill(Qt::red);
+    QPixmap dest = src;
+    dest.fill(Qt::blue);
+    QCOMPARE(dest.devicePixelRatio(), dpr);
+}
+
 void tst_QPixmap::dprPassthrough()
 {
     const qreal dpr = 2;