Fixed holes in border image drawing by introducing new API.

When rasterizing two adjacent QRectFs it's important that the shared x
or y-edges have the exact same coordinates, or there might be a hole or
an overlapping pixel when they are rasterized. Since the
drawPixmapFragments API was based on a center position and a scale, it
can not be used for this purpose, as the in the situation of two
horizontally adjacent rectangles the right edge of the left-most rect
and the left edge of the right-most edge are computed differently. Thus
rounding errors can cause them to not be equal, especially when there's
also a scaling / translating painter transform involved.

Thus, to not sacrifice performance, we need to introduce a new
drawPixmapFragments API that's simply takes an array of target
rectangles and an array of source rectangles. It should give a slight
performance boost for the border pixmap use case as well, since there
are less floating point multiplications / divisions involved.

Task-number: QTBUG-19079
Reviewed-by: Kim

1 files changed, 6 insertions, 5 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index 626100a498..d77ef8227e 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -2396,12 +2396,13 @@ void QRasterPaintEngine::drawImage(const QRectF &r, const QImage &img, const QRe
         d->image_filler_xform.setupMatrix(copy, s->flags.bilinear);
 
         if (!s->flags.antialiased && s->matrix.type() == QTransform::TxScale) {
-            QRectF rr = s->matrix.mapRect(r);
+            QPointF rr_tl = s->matrix.map(r.topLeft());
+            QPointF rr_br = s->matrix.map(r.bottomRight());
 
-            const int x1 = qRound(rr.x());
-            const int y1 = qRound(rr.y());
-            const int x2 = qRound(rr.right());
-            const int y2 = qRound(rr.bottom());
+            const int x1 = qRound(rr_tl.x());
+            const int y1 = qRound(rr_tl.y());
+            const int x2 = qRound(rr_br.x());
+            const int y2 = qRound(rr_br.y());
 
             fillRect_normalized(QRect(x1, y1, x2-x1, y2-y1), &d->image_filler_xform, d);
             return;