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

2 files changed, 52 insertions, 25 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index e249b3e..788b722 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -2664,7 +2664,13 @@ void QRasterPaintEngine::drawImage(const QRectF &r, const QImage &img, const QRe
 
         QRectF rr = r;
         rr.translate(s->matrix.dx(), s->matrix.dy());
-        fillRect_normalized(toRect_normalized(rr), &d->image_filler, d);
+
+        const int x1 = qRound(rr.x());
+        const int y1 = qRound(rr.y());
+        const int x2 = qRound(rr.right());
+        const int y2 = qRound(rr.bottom());
+
+        fillRect_normalized(QRect(x1, y1, x2-x1, y2-y1), &d->image_filler, d);
     }
 }
 
@@ -5147,7 +5153,11 @@ void QSpanData::adjustSpanMethods()
 
 void QSpanData::setupMatrix(const QTransform &matrix, int bilin)
 {
-    QTransform inv = matrix.inverted();
+    QTransform delta;
+    // make sure we round off correctly in qdrawhelper.cpp
+    delta.translate(1.0 / 65536, 1.0 / 65536);
+
+    QTransform inv = (delta * matrix).inverted();
     m11 = inv.m11();
     m12 = inv.m12();
     m13 = inv.m13();
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);