Fixed QRasterPaintEngine::drawImage() for 1x1 source rectangles.

QRasterPaintEngine::drawImage() used an optimized code path when the
source rectangle was 1x1. It would sample the source image at the
source rectangle's top-left corner and use the sampled color to fill
the entire target rectangle. There were two bugs, however:

1) The sampled color was assumed to be non-premultiplied, so you could
   end up with premultiplying the color twice. This was fixed by
   avoiding premultiplying a second time if the source image has a
   premultiplied format.

2) Since the source rectangle is a QRectF, it could easily cross pixel
   boundaries even if it's 1x1. In this case, it is not correct to fill
   the target rectangle with a single color. This was fixed by checking
   if the entire source rectangle is contained in a single pixel before
   taking the optimized code path.

Task-number: 256950
Reviewed-by: Trond

1 files changed, 34 insertions, 2 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index 547818c..63c4e32 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -2544,12 +2544,44 @@ void QRasterPaintEngine::drawImage(const QRectF &r, const QImage &img, const QRe
     Q_D(QRasterPaintEngine);
     QRasterPaintEngineState *s = state();
     const bool aa = s->flags.antialiased || s->flags.bilinear;
-    if (!aa && sr.size() == QSize(1, 1)) {
+    int sr_l = qFloor(sr.left());
+    int sr_r = qCeil(sr.right()) - 1;
+    int sr_t = qFloor(sr.top());
+    int sr_b = qCeil(sr.bottom()) - 1;
+
+    if (!aa && sr_l == sr_r && sr_t == sr_b) {
         // as fillRect will apply the aliased coordinate delta we need to
         // subtract it here as we don't use it for image drawing
         QTransform old = s->matrix;
         s->matrix = s->matrix * QTransform::fromTranslate(-aliasedCoordinateDelta, -aliasedCoordinateDelta);
-        fillRect(r, QColor::fromRgba(img.pixel(sr.x(), sr.y())));
+
+        // Do whatever fillRect() does, but without premultiplying the color if it's already premultiplied.
+        QRgb color = img.pixel(sr_l, sr_t);
+        switch (img.format()) {
+        case QImage::Format_ARGB32_Premultiplied:
+        case QImage::Format_ARGB8565_Premultiplied:
+        case QImage::Format_ARGB6666_Premultiplied:
+        case QImage::Format_ARGB8555_Premultiplied:
+        case QImage::Format_ARGB4444_Premultiplied:
+            // Combine premultiplied color with the opacity set on the painter.
+            d->solid_color_filler.solid.color =
+                ((((color & 0x00ff00ff) * s->intOpacity) >> 8) & 0x00ff00ff)
+                | ((((color & 0xff00ff00) >> 8) * s->intOpacity) & 0xff00ff00);
+            break;
+        default:
+            d->solid_color_filler.solid.color = PREMUL(ARGB_COMBINE_ALPHA(color, s->intOpacity));
+            break;
+        }
+
+        if ((d->solid_color_filler.solid.color & 0xff000000) == 0
+            && s->composition_mode == QPainter::CompositionMode_SourceOver) {
+            return;
+        }
+
+        d->solid_color_filler.clip = d->clip();
+        d->solid_color_filler.adjustSpanMethods();
+        fillRect(r, &d->solid_color_filler);
+
         s->matrix = old;
         return;
     }