Fixed raster bug causing fully clipped images to be partially blended.

The blend functions assume the width / height of the images being
blended to be greater than 0. A width of 0 caused the first iteration of
a duff's device memcpy (QT_MEMCPY_USHORT) to be executed, thus blending
8 pixels instead of none.

BT: yes
Task-number: 255014
Reviewed-by: Trond

2 files changed, 28 insertions, 2 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index 58ffb02..1a1c204 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -1053,7 +1053,7 @@ void QRasterPaintEnginePrivate::drawImage(const QPointF &pt,
         int d = x + iw - cx2;
         iw -= d;
     }
-    if (iw < 0)
+    if (iw <= 0)
         return;
 
     // adapt the y paremeters...
@@ -1070,7 +1070,7 @@ void QRasterPaintEnginePrivate::drawImage(const QPointF &pt,
         int d = y + ih - cy2;
         ih -= d;
     }
-    if (ih < 0)
+    if (ih <= 0)
         return;
 
     // call the blend function...
diff --git a/tests/auto/qpainter/tst_qpainter.cpp b/tests/auto/qpainter/tst_qpainter.cpp
index 87f9c13..8d6c9d2 100644
--- a/tests/auto/qpainter/tst_qpainter.cpp
+++ b/tests/auto/qpainter/tst_qpainter.cpp
@@ -215,6 +215,7 @@ private slots:
     void imageCoordinateLimit();
     void imageBlending_data();
     void imageBlending();
+    void imageBlending_clipped();
 
     void paintOnNullPixmap();
     void checkCompositionMode();
@@ -3792,6 +3793,31 @@ void tst_QPainter::imageBlending()
     }
 }
 
+void tst_QPainter::imageBlending_clipped()
+{
+    QImage src(20, 20, QImage::Format_RGB16);
+    QPainter p(&src);
+    p.fillRect(src.rect(), Qt::red);
+    p.end();
+
+    QImage dst(40, 20, QImage::Format_RGB16);
+    p.begin(&dst);
+    p.fillRect(dst.rect(), Qt::white);
+    p.end();
+
+    QImage expected = dst;
+
+    p.begin(&dst);
+    p.setClipRect(QRect(23, 0, 20, 20));
+
+    // should be completely clipped
+    p.drawImage(QRectF(3, 0, 20, 20), src);
+    p.end();
+
+    // dst should be left unchanged
+    QCOMPARE(dst, expected);
+}
+
 void tst_QPainter::paintOnNullPixmap()
 {
     QPixmap pix(16, 16);