Fixed inconsistent QPainter fill rules for aliased painting.

Qt 5 is the time to get rid of all the old inconsistencies in the raster
paint engine caused by trying to preserve the old X11 based
coordinate system where (0, 0) is in the center of the top-left pixel
instead of the upper left corner of said pixel. However, this was only
adhered for line drawing and path / rect filling, and not for image or
pixmap drawing and not at all when doing antialiased painting. By
defining the antialiased coordinate system as being the right one and
letting the aliased fill rules follow from that we finally end up with
some consistent behavior that doesn't lead to surprises and workarounds
in application code.

It is still possible for applications to get the old behavior by
setting the QPainter::Qt4CompatiblePainting render hint. This should
make porting easier for the few cases where an application relies on the
aliased fill rules we used to have in Qt 4.

Task-number: QTBUG-27500
Change-Id: If86b95e77d838ec83033d64af86632b9a73c74a9
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 30 insertions, 9 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index 5228fdcf1d..e0eab8dc73 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -644,6 +644,7 @@ QRasterPaintEngineState::QRasterPaintEngineState()
     flags.fast_pen = true;
     flags.antialiased = false;
     flags.bilinear = false;
+    flags.legacy_rounding = false;
     flags.fast_text = true;
     flags.int_xform = true;
     flags.tx_noshear = true;
@@ -927,6 +928,7 @@ void QRasterPaintEngine::renderHintsChanged()
 
     s->flags.antialiased = bool(s->renderHints & QPainter::Antialiasing);
     s->flags.bilinear = bool(s->renderHints & QPainter::SmoothPixmapTransform);
+    s->flags.legacy_rounding = !bool(s->renderHints & QPainter::Antialiasing) && bool(s->renderHints & QPainter::Qt4CompatiblePainting);
 
     if (was_aa != s->flags.antialiased)
         s->strokeFlags |= DirtyHints;
@@ -1524,6 +1526,7 @@ void QRasterPaintEngine::drawRects(const QRect *rects, int rectCount)
         QRectVectorPath path;
         if (s->flags.fast_pen) {
             QCosmeticStroker stroker(s, d->deviceRect);
+            stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
             for (int i = 0; i < rectCount; ++i) {
                 path.set(rects[i]);
                 stroker.drawPath(path);
@@ -1570,6 +1573,7 @@ void QRasterPaintEngine::drawRects(const QRectF *rects, int rectCount)
             QRectVectorPath path;
             if (s->flags.fast_pen) {
                 QCosmeticStroker stroker(s, d->deviceRect);
+                stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
                 for (int i = 0; i < rectCount; ++i) {
                     path.set(rects[i]);
                     stroker.drawPath(path);
@@ -1603,6 +1607,7 @@ void QRasterPaintEngine::stroke(const QVectorPath &path, const QPen &pen)
 
     if (s->flags.fast_pen) {
         QCosmeticStroker stroker(s, d->deviceRect);
+        stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
         stroker.drawPath(path);
     } else if (s->flags.non_complex_pen && path.shape() == QVectorPath::LinesHint) {
         qreal width = s->lastPen.isCosmetic()
@@ -1658,12 +1663,16 @@ void QRasterPaintEngine::stroke(const QVectorPath &path, const QPen &pen)
         QPaintEngineEx::stroke(path, pen);
 }
 
-static inline QRect toNormalizedFillRect(const QRectF &rect)
+QRect QRasterPaintEngine::toNormalizedFillRect(const QRectF &rect)
 {
-    int x1 = qRound(rect.x() + aliasedCoordinateDelta);
-    int y1 = qRound(rect.y() + aliasedCoordinateDelta);
-    int x2 = qRound(rect.right() + aliasedCoordinateDelta);
-    int y2 = qRound(rect.bottom() + aliasedCoordinateDelta);
+    QRasterPaintEngineState *s = state();
+
+    qreal delta = s->flags.legacy_rounding ? aliasedCoordinateDelta : qreal(0);
+
+    int x1 = qRound(rect.x() + delta);
+    int y1 = qRound(rect.y() + delta);
+    int x2 = qRound(rect.right() + delta);
+    int y2 = qRound(rect.bottom() + delta);
 
     if (x2 < x1)
         qSwap(x1, x2);
@@ -1941,6 +1950,7 @@ void QRasterPaintEngine::drawPolygon(const QPointF *points, int pointCount, Poly
         QVectorPath vp((qreal *) points, pointCount, 0, QVectorPath::polygonFlags(mode));
         if (s->flags.fast_pen) {
             QCosmeticStroker stroker(s, d->deviceRect);
+            stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
             stroker.drawPath(vp);
         } else {
             QPaintEngineEx::stroke(vp, s->lastPen);
@@ -2005,6 +2015,7 @@ void QRasterPaintEngine::drawPolygon(const QPoint *points, int pointCount, Polyg
 
         if (s->flags.fast_pen) {
             QCosmeticStroker stroker(s, d->deviceRect);
+            stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
             stroker.drawPath(vp);
         } else {
             QPaintEngineEx::stroke(vp, s->lastPen);
@@ -2233,7 +2244,9 @@ void QRasterPaintEngine::drawImage(const QRectF &r, const QImage &img, const QRe
         // as fillRect will apply the aliased coordinate delta we need to
         // subtract it here as we don't use it for image drawing
         QTransform old = s->matrix;
-        s->matrix = s->matrix * QTransform::fromTranslate(-aliasedCoordinateDelta, -aliasedCoordinateDelta);
+
+        if (s->flags.legacy_rounding)
+            s->matrix = s->matrix * QTransform::fromTranslate(-aliasedCoordinateDelta, -aliasedCoordinateDelta);
 
         // Do whatever fillRect() does, but without premultiplying the color if it's already premultiplied.
         QRgb color = img.pixel(sr_l, sr_t);
@@ -2376,8 +2389,9 @@ void QRasterPaintEngine::drawImage(const QRectF &r, const QImage &img, const QRe
         if (s->flags.tx_noshear || s->matrix.type() == QTransform::TxScale) {
             d->initializeRasterizer(&d->image_filler_xform);
             d->rasterizer->setAntialiased(s->flags.antialiased);
+            d->rasterizer->setLegacyRoundingEnabled(s->flags.legacy_rounding);
 
-            const QPointF offs = s->flags.antialiased ? QPointF() : QPointF(aliasedCoordinateDelta, aliasedCoordinateDelta);
+            const QPointF offs = s->flags.legacy_rounding ? QPointF(aliasedCoordinateDelta, aliasedCoordinateDelta) : QPointF();
 
             const QRectF &rect = r.normalized();
             const QPointF a = s->matrix.map((rect.topLeft() + rect.bottomLeft()) * 0.5f) - offs;
@@ -2390,7 +2404,7 @@ void QRasterPaintEngine::drawImage(const QRectF &r, const QImage &img, const QRe
             return;
         }
 #endif
-        const qreal offs = s->flags.antialiased ? qreal(0) : aliasedCoordinateDelta;
+        const qreal offs = s->flags.legacy_rounding ? aliasedCoordinateDelta : qreal(0);
         QPainterPath path;
         path.addRect(r);
         QTransform m = s->matrix;
@@ -2471,6 +2485,7 @@ void QRasterPaintEngine::drawTiledPixmap(const QRectF &r, const QPixmap &pixmap,
         if (s->flags.tx_noshear || s->matrix.type() == QTransform::TxScale) {
             d->initializeRasterizer(&d->image_filler_xform);
             d->rasterizer->setAntialiased(s->flags.antialiased);
+            d->rasterizer->setLegacyRoundingEnabled(s->flags.legacy_rounding);
 
             const QRectF &rect = r.normalized();
             const QPointF a = s->matrix.map((rect.topLeft() + rect.bottomLeft()) * 0.5f);
@@ -2802,7 +2817,7 @@ bool QRasterPaintEngine::drawCachedGlyphs(int numGlyphs, const glyph_t *glyphs,
             rightShift = 3; // divide by 8
 
         int margin = fontEngine->glyphMargin(glyphType);
-        const QFixed offs = QFixed::fromReal(aliasedCoordinateDelta);
+        const QFixed offs = s->flags.legacy_rounding ? QFixed::fromReal(aliasedCoordinateDelta) : QFixed();
         const uchar *bits = image.bits();
         for (int i=0; i<numGlyphs; ++i) {
 
@@ -3078,6 +3093,7 @@ void QRasterPaintEngine::drawPoints(const QPointF *points, int pointCount)
     }
 
     QCosmeticStroker stroker(s, d->deviceRect);
+    stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
     stroker.drawPoints(points, pointCount);
 }
 
@@ -3097,6 +3113,7 @@ void QRasterPaintEngine::drawPoints(const QPoint *points, int pointCount)
     }
 
     QCosmeticStroker stroker(s, d->deviceRect);
+    stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
     stroker.drawPoints(points, pointCount);
 }
 
@@ -3117,6 +3134,7 @@ void QRasterPaintEngine::drawLines(const QLine *lines, int lineCount)
 
     if (s->flags.fast_pen) {
         QCosmeticStroker stroker(s, d->deviceRect);
+        stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
         for (int i=0; i<lineCount; ++i) {
             const QLine &l = lines[i];
             stroker.drawLine(l.p1(), l.p2());
@@ -3188,6 +3206,7 @@ void QRasterPaintEngine::drawLines(const QLineF *lines, int lineCount)
         return;
     if (s->flags.fast_pen) {
         QCosmeticStroker stroker(s, d->deviceRect);
+        stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
         for (int i=0; i<lineCount; ++i) {
             QLineF line = lines[i];
             stroker.drawLine(line.p1(), line.p2());
@@ -3420,6 +3439,7 @@ void QRasterPaintEnginePrivate::initializeRasterizer(QSpanData *data)
     QRasterPaintEngineState *s = q->state();
 
     rasterizer->setAntialiased(s->flags.antialiased);
+    rasterizer->setLegacyRoundingEnabled(s->flags.legacy_rounding);
 
     QRect clipRect(deviceRect);
     ProcessSpans blend;
@@ -3484,6 +3504,7 @@ void QRasterPaintEnginePrivate::rasterize(QT_FT_Outline *outline,
 
     if (!s->flags.antialiased) {
         rasterizer->setAntialiased(s->flags.antialiased);
+        rasterizer->setLegacyRoundingEnabled(s->flags.legacy_rounding);
         rasterizer->setClipRect(deviceRect);
         rasterizer->initialize(callback, userData);