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, 16 insertions, 0 deletions

diff --git a/src/gui/painting/qpaintengineex.cpp b/src/gui/painting/qpaintengineex.cpp
index 5105d9a963..6df410b27d 100644
--- a/src/gui/painting/qpaintengineex.cpp
+++ b/src/gui/painting/qpaintengineex.cpp
@@ -1003,6 +1003,22 @@ void QPaintEngineEx::drawPixmapFragments(const QPainter::PixmapFragment *fragmen
     transformChanged();
 }
 
+void QPaintEngineEx::drawPixmapFragments(const QRectF *targetRects, const QRectF *sourceRects, int fragmentCount,
+                                         const QPixmap &pixmap, QPainter::PixmapFragmentHints /*hints*/)
+{
+    if (pixmap.isNull())
+        return;
+
+    if (sourceRects) {
+        for (int i = 0; i < fragmentCount; ++i)
+            drawPixmap(targetRects[i], pixmap, sourceRects[i]);
+    } else {
+        QRectF sourceRect = pixmap.rect();
+        for (int i = 0; i < fragmentCount; ++i)
+            drawPixmap(targetRects[i], pixmap, sourceRect);
+    }
+}
+
 void QPaintEngineEx::setState(QPainterState *s)
 {
     QPaintEngine::state = s;