Improve performance of clipping to a scaled QRectF

Clipping to a scaled QRectF was so far hitting the slow
code path in the raster paintengine that generates clip spans
for every line. This is not needed as we also clip translated
QRectF's to integer rects.

This patch does the same for scaled rectangles and ensures the
clipping really happens at the closest pixel boundary.

Reviewed-by: Samuel

2 files changed, 25 insertions, 10 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index 89202ac..4d06c9f 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -1212,7 +1212,7 @@ void QRasterPaintEngine::clip(const QVectorPath &path, Qt::ClipOperation op)
     // There are some cases that are not supported by clip(QRect)
     if (op != Qt::UniteClip && (op != Qt::IntersectClip || !s->clip
                                 || s->clip->hasRectClip || s->clip->hasRegionClip)) {
-        if (s->matrix.type() <= QTransform::TxTranslate
+        if (s->matrix.type() <= QTransform::TxScale
             && ((path.shape() == QVectorPath::RectangleHint)
                 || (isRect(points, path.elementCount())
                     && (!types || (types[0] == QPainterPath::MoveToElement
@@ -1224,8 +1224,8 @@ void QRasterPaintEngine::clip(const QVectorPath &path, Qt::ClipOperation op)
 #endif
 
             QRectF r(points[0], points[1], points[4]-points[0], points[5]-points[1]);
-            clip(r.toRect(), op);
-            return;
+            if (setClipRectInDeviceCoords(s->matrix.mapRect(r).toRect(), op))
+                return;
         }
     }
 
@@ -1286,7 +1286,6 @@ void QRasterPaintEngine::clip(const QRect &rect, Qt::ClipOperation op)
     qDebug() << "QRasterPaintEngine::clip(): " << rect << op;
 #endif
 
-    Q_D(QRasterPaintEngine);
     QRasterPaintEngineState *s = state();
 
     if (op == Qt::NoClip) {
@@ -1296,11 +1295,23 @@ void QRasterPaintEngine::clip(const QRect &rect, Qt::ClipOperation op)
         QPaintEngineEx::clip(rect, op);
         return;
 
-    } else if (op == Qt::ReplaceClip || s->clip == 0) {
+    } else if (!setClipRectInDeviceCoords(s->matrix.mapRect(rect), op)) {
+        QPaintEngineEx::clip(rect, op);
+        return;
+    }
+}
+
+
+bool QRasterPaintEngine::setClipRectInDeviceCoords(const QRect &r, Qt::ClipOperation op)
+{
+    Q_D(QRasterPaintEngine);
+    QRect clipRect = r & d->deviceRect;
+    QRasterPaintEngineState *s = state();
+
+    if (op == Qt::ReplaceClip || s->clip == 0) {
 
         // No current clip, hence we intersect with sysclip and be
         // done with it...
-        QRect clipRect = s->matrix.mapRect(rect) & d->deviceRect;
         QRegion clipRegion = systemClip();
         QClipData *clip = new QClipData(d->rasterBuffer->height());
 
@@ -1316,12 +1327,11 @@ void QRasterPaintEngine::clip(const QRect &rect, Qt::ClipOperation op)
         s->clip->enabled = true;
         s->flags.has_clip_ownership = true;
 
-    } else { // intersect clip with current clip
+    } else if (op == Qt::IntersectClip){ // intersect clip with current clip
         QClipData *base = s->clip;
 
         Q_ASSERT(base);
         if (base->hasRectClip || base->hasRegionClip) {
-            QRect clipRect = s->matrix.mapRect(rect) & d->deviceRect;
             if (!s->flags.has_clip_ownership) {
                 s->clip = new QClipData(d->rasterBuffer->height());
                 s->flags.has_clip_ownership = true;
@@ -1332,11 +1342,14 @@ void QRasterPaintEngine::clip(const QRect &rect, Qt::ClipOperation op)
                 s->clip->setClipRegion(base->clipRegion & clipRect);
             s->clip->enabled = true;
         } else {
-            QPaintEngineEx::clip(rect, op);
-            return;
+            return false;
         }
+    } else {
+        return false;
     }
+
     qrasterpaintengine_dirty_clip(d, s);
+    return true;
 }
 
 
diff --git a/src/gui/painting/qpaintengine_raster_p.h b/src/gui/painting/qpaintengine_raster_p.h
index 1016f8d..7d4d3b6 100644
--- a/src/gui/painting/qpaintengine_raster_p.h
+++ b/src/gui/painting/qpaintengine_raster_p.h
@@ -266,6 +266,8 @@ private:
     void drawGlyphsS60(const QPointF &p, const QTextItemInt &ti);
 #endif // Q_OS_SYMBIAN && QT_NO_FREETYPE
 
+    bool setClipRectInDeviceCoords(const QRect &r, Qt::ClipOperation op);
+
     inline void ensureBrush(const QBrush &brush) {
         if (!qbrush_fast_equals(state()->lastBrush, brush) || (brush.style() != Qt::NoBrush && state()->fillFlags))
             updateBrush(brush);