Fix blending of RGB32 on RGB32 with partial opacity

The alpha channel of an RGB32 image was not properly ignored when doing
blending with partial opacity.

Now the alpha value is properly ignored, which is both more correct
and faster. This also makes SSE2 and AVX2 implementations match NEON
which was already doing the right thing (though had dead code for
doing it wrong).

Change-Id: I4613b8d70ed8c2e36ced10baaa7a4a55bd36a940
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
index 254ab1f8ad..c729b2f94c 100644
--- a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
+++ b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
@@ -300,6 +300,8 @@ private slots:
 
     void QTBUG56252();
 
+    void blendNullRGB32();
+
 private:
     void fillData();
     void setPenColor(QPainter& p);
@@ -5139,6 +5141,24 @@ void tst_QPainter::QTBUG56252()
     // If no crash or illegal memory read, all is fine
 }
 
+void tst_QPainter::blendNullRGB32()
+{
+    quint32 data[16] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+
+    QImage nullImage((const uchar*)data, 16, 1,  QImage::Format_RGB32);
+    QImage image(16, 1, QImage::Format_RGB32);
+    image.fill(Qt::white);
+
+    QPainter paint(&image);
+    paint.setCompositionMode(QPainter::CompositionMode_Source);
+    paint.setOpacity(0.5);
+    paint.drawImage(0, 0, nullImage);
+    paint.end();
+
+    for (int i=0; i < image.width(); ++i)
+        QVERIFY(image.pixel(i,0) != 0xffffffff);
+}
+
 QTEST_MAIN(tst_QPainter)
 
 #include "tst_qpainter.moc"