Ensured correct rounding of scaled image drawing at non-integer coords.

Images coordinates should simply be rounded and are not to be subject
to the aliased coordinate delta. The patch also adds a tiny delta in
QSpanData::setupMatrix() to ensure coordinates for fetching from source
images are rounded the opposite direction of the target rectangle.
This removes a lot of artifacts when trying to do border-image based
drawing on non-integer coordinates. A new qps test for border-image
drawing is included.

Task-number: 251561
Reviewed-by: Trond

1 files changed, 40 insertions, 23 deletions

diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index 759bd7e..afc4211 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -5142,6 +5142,11 @@ void QPainter::drawConvexPolygon(const QPointF *points, int pointCount)
     d->engine->drawPolygon(points, pointCount, QPaintEngine::ConvexMode);
 }
 
+static inline QPointF roundInDeviceCoordinates(const QPointF &p, const QTransform &m)
+{
+    return m.inverted().map(QPointF(m.map(p).toPoint()));
+}
+
 /*!
     \fn void QPainter::drawPixmap(const QRectF &target, const QPixmap &pixmap, const QRectF &source)
 
@@ -5210,11 +5215,12 @@ void QPainter::drawPixmap(const QPointF &p, const QPixmap &pm)
         || (d->state->opacity != 1.0 && !d->engine->hasFeature(QPaintEngine::ConstantOpacity)))
     {
         save();
-        // If there is no scaling or transformation involved we have to make sure we use the
+        // If there is no rotation involved we have to make sure we use the
         // antialiased and not the aliased coordinate system by rounding the coordinates.
-        if (d->state->matrix.type() <= QTransform::TxTranslate) {
-            x = qRound(x + d->state->matrix.dx()) - d->state->matrix.dx();
-            y = qRound(y + d->state->matrix.dy()) - d->state->matrix.dy();
+        if (d->state->matrix.type() <= QTransform::TxScale) {
+            const QPointF p = roundInDeviceCoordinates(QPointF(x, y), d->state->matrix);
+            x = p.x();
+            y = p.y();
         }
         translate(x, y);
         setBackgroundMode(Qt::TransparentMode);
@@ -5324,16 +5330,21 @@ void QPainter::drawPixmap(const QRectF &r, const QPixmap &pm, const QRectF &sr)
         || ((sw != w || sh != h) && !d->engine->hasFeature(QPaintEngine::PixmapTransform)))
     {
         save();
-        // If there is no scaling or transformation involved we have to make sure we use the
+        // If there is no rotation involved we have to make sure we use the
         // antialiased and not the aliased coordinate system by rounding the coordinates.
+        if (d->state->matrix.type() <= QTransform::TxScale) {
+            const QPointF p = roundInDeviceCoordinates(QPointF(x, y), d->state->matrix);
+            x = p.x();
+            y = p.y();
+        }
+
         if (d->state->matrix.type() <= QTransform::TxTranslate && sw == w && sh == h) {
-            x = qRound(x + d->state->matrix.dx()) - d->state->matrix.dx();
-            y = qRound(y + d->state->matrix.dy()) - d->state->matrix.dy();
             sx = qRound(sx);
             sy = qRound(sy);
             sw = qRound(sw);
             sh = qRound(sh);
         }
+
         translate(x, y);
         scale(w / sw, h / sh);
         setBackgroundMode(Qt::TransparentMode);
@@ -5483,11 +5494,12 @@ void QPainter::drawImage(const QPointF &p, const QImage &image)
         || (d->state->opacity != 1.0 && !d->engine->hasFeature(QPaintEngine::ConstantOpacity)))
     {
         save();
-        // If there is no scaling or transformation involved we have to make sure we use the
+        // If there is no rotation involved we have to make sure we use the
         // antialiased and not the aliased coordinate system by rounding the coordinates.
-        if (d->state->matrix.type() <= QTransform::TxTranslate) {
-            x = qRound(x + d->state->matrix.dx()) - d->state->matrix.dx();
-            y = qRound(y + d->state->matrix.dy()) - d->state->matrix.dy();
+        if (d->state->matrix.type() <= QTransform::TxScale) {
+            const QPointF p = roundInDeviceCoordinates(QPointF(x, y), d->state->matrix);
+            x = p.x();
+            y = p.y();
         }
         translate(x, y);
         setBackgroundMode(Qt::TransparentMode);
@@ -5586,11 +5598,15 @@ void QPainter::drawImage(const QRectF &targetRect, const QImage &image, const QR
         || (d->state->opacity != 1.0 && !d->engine->hasFeature(QPaintEngine::ConstantOpacity)))
     {
         save();
-        // If there is no scaling or transformation involved we have to make sure we use the
+        // If there is no rotation involved we have to make sure we use the
         // antialiased and not the aliased coordinate system by rounding the coordinates.
+        if (d->state->matrix.type() <= QTransform::TxScale) {
+            const QPointF p = roundInDeviceCoordinates(QPointF(x, y), d->state->matrix);
+            x = p.x();
+            y = p.y();
+        }
+
         if (d->state->matrix.type() <= QTransform::TxTranslate && sw == w && sh == h) {
-            x = qRound(x + d->state->matrix.dx()) - d->state->matrix.dx();
-            y = qRound(y + d->state->matrix.dy()) - d->state->matrix.dy();
             sx = qRound(sx);
             sy = qRound(sy);
             sw = qRound(sw);
@@ -6333,17 +6349,18 @@ void QPainter::drawTiledPixmap(const QRectF &r, const QPixmap &pixmap, const QPo
         setBrush(QBrush(d->state->pen.color(), pixmap));
         setPen(Qt::NoPen);
 
-        // If there is no scaling or transformation involved we have to make sure we use the
+        // If there is no rotation involved we have to make sure we use the
         // antialiased and not the aliased coordinate system by rounding the coordinates.
-        if (d->state->matrix.type() <= QTransform::TxTranslate) {
-            qreal x = qRound(r.x() + d->state->matrix.dx()) - d->state->matrix.dx();
-            qreal y = qRound(r.y() + d->state->matrix.dy()) - d->state->matrix.dy();
-            qreal w = qRound(r.width());
-            qreal h = qRound(r.height());
-            sx = qRound(sx);
-            sy = qRound(sy);
+        if (d->state->matrix.type() <= QTransform::TxScale) {
+            const QPointF p = roundInDeviceCoordinates(r.topLeft(), d->state->matrix);
+
+            if (d->state->matrix.type() <= QTransform::TxTranslate) {
+                sx = qRound(sx);
+                sy = qRound(sy);
+            }
+
             setBrushOrigin(QPointF(r.x()-sx, r.y()-sy));
-            drawRect(QRectF(x, y, w, h));
+            drawRect(QRectF(p, r.size()));
         } else {
             setBrushOrigin(QPointF(r.x()-sx, r.y()-sy));
             drawRect(r);