QGraphicsBlurEffect: Fix for high DPI scaling

Preserve the device pixel ratio in the various helper functions
and when drawing.

Task-number: QTBUG-60026
Change-Id: Ieac9360b00044b6aedd0d3e1ad6e3b16d436f20f
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

2 files changed, 10 insertions, 1 deletions

diff --git a/src/widgets/effects/qpixmapfilter.cpp b/src/widgets/effects/qpixmapfilter.cpp
index bb949fcebf..999e551af4 100644
--- a/src/widgets/effects/qpixmapfilter.cpp
+++ b/src/widgets/effects/qpixmapfilter.cpp
@@ -719,6 +719,7 @@ void expblur(QImage &img, qreal radius, bool improvedQuality = false, int transp
     }
 
     QImage temp(img.height(), img.width(), img.format());
+    temp.setDevicePixelRatio(img.devicePixelRatioF());
     if (transposed >= 0) {
         if (img.depth() == 8) {
             qt_memrotate270(reinterpret_cast<const quint8*>(img.bits()),
@@ -780,6 +781,7 @@ Q_WIDGETS_EXPORT QImage qt_halfScaled(const QImage &source)
     if (source.format() == QImage::Format_Indexed8 || source.format() == QImage::Format_Grayscale8) {
         // assumes grayscale
         QImage dest(source.width() / 2, source.height() / 2, srcImage.format());
+        dest.setDevicePixelRatio(source.devicePixelRatioF());
 
         const uchar *src = reinterpret_cast<const uchar*>(const_cast<const QImage &>(srcImage).bits());
         int sx = srcImage.bytesPerLine();
@@ -801,6 +803,7 @@ Q_WIDGETS_EXPORT QImage qt_halfScaled(const QImage &source)
         return dest;
     } else if (source.format() == QImage::Format_ARGB8565_Premultiplied) {
         QImage dest(source.width() / 2, source.height() / 2, srcImage.format());
+        dest.setDevicePixelRatio(source.devicePixelRatioF());
 
         const uchar *src = reinterpret_cast<const uchar*>(const_cast<const QImage &>(srcImage).bits());
         int sx = srcImage.bytesPerLine();
@@ -837,6 +840,7 @@ Q_WIDGETS_EXPORT QImage qt_halfScaled(const QImage &source)
     }
 
     QImage dest(source.width() / 2, source.height() / 2, srcImage.format());
+    dest.setDevicePixelRatio(source.devicePixelRatioF());
 
     const quint32 *src = reinterpret_cast<const quint32*>(const_cast<const QImage &>(srcImage).bits());
     int sx = srcImage.bytesPerLine() >> 2;
@@ -881,7 +885,7 @@ Q_WIDGETS_EXPORT void qt_blurImage(QPainter *p, QImage &blurImage, qreal radius,
     if (p) {
         p->scale(scale, scale);
         p->setRenderHint(QPainter::SmoothPixmapTransform);
-        p->drawImage(QRect(0, 0, blurImage.width(), blurImage.height()), blurImage);
+        p->drawImage(QRect(QPoint(0, 0), blurImage.size() / blurImage.devicePixelRatioF()), blurImage);
     }
 }
 
diff --git a/tests/auto/widgets/effects/qpixmapfilter/tst_qpixmapfilter.cpp b/tests/auto/widgets/effects/qpixmapfilter/tst_qpixmapfilter.cpp
index 08f4944d49..7d7c1e79a9 100644
--- a/tests/auto/widgets/effects/qpixmapfilter/tst_qpixmapfilter.cpp
+++ b/tests/auto/widgets/effects/qpixmapfilter/tst_qpixmapfilter.cpp
@@ -390,6 +390,7 @@ QT_END_NAMESPACE
 void tst_QPixmapFilter::blurIndexed8()
 {
     QImage img(16, 32, QImage::Format_Indexed8);
+    img.setDevicePixelRatio(2);
     img.setColorCount(256);
     for (int i = 0; i < 256; ++i)
         img.setColor(i, qRgb(i, i, i));
@@ -399,9 +400,13 @@ void tst_QPixmapFilter::blurIndexed8()
     QImage original = img;
     qt_blurImage(img, 10, true, false);
     QCOMPARE(original.size(), img.size());
+    QVERIFY2(qFuzzyCompare(img.devicePixelRatioF(), qreal(2)),
+             QByteArray::number(img.devicePixelRatioF()).constData());
 
     original = img;
     qt_blurImage(img, 10, true, true);
+    QVERIFY2(qFuzzyCompare(img.devicePixelRatioF(), qreal(2)),
+             QByteArray::number(img.devicePixelRatioF()).constData());
     QCOMPARE(original.size(), QSize(img.height(), img.width()));
 }