When using complex transformations rendering goes easily off by one pixel.

This happens because of differences in OpenVG and Qt pixel center point
handling. Currently there is no easy generic way to adjust Qt pixels to
match OpenVG. This patch adjusts pixels for simple affine transformations
by rounding them.

Task-number: QT-3791
Reviewed-by: Jason Barron

1 files changed, 92 insertions, 66 deletions

diff --git a/src/openvg/qpaintengine_vg.cpp b/src/openvg/qpaintengine_vg.cpp
index 75e5a60..1b0c5e8 100644
--- a/src/openvg/qpaintengine_vg.cpp
+++ b/src/openvg/qpaintengine_vg.cpp
@@ -196,7 +196,9 @@ public:
 #endif
 
     QTransform transform;   // Currently active transform.
-    bool simpleTransform;   // True if the transform is simple (non-projective).
+    bool affineTransform;   // True if the transform is non-projective.
+    bool simpleTransform;   // True if the transform is simple translate
+                            // or 0, 90, 180, and 270 degree rotation
     qreal penScale;         // Pen scaling factor from "transform".
 
     QTransform pathTransform;  // Calculated VG path transformation.
@@ -372,6 +374,7 @@ void QVGPaintEnginePrivate::init()
     roundRectPath = 0;
 #endif
 
+    affineTransform = true;
     simpleTransform = true;
     pathTransformSet = false;
     penScale = 1.0;
@@ -524,12 +527,59 @@ void QVGPaintEnginePrivate::setTransform
     vgLoadMatrix(mat);
 }
 
+// Determine if a co-ordinate transform is simple enough to allow
+// rectangle-based clipping with vgMask() and rounding translation
+// to integers. Simple transforms most often result from origin translations.
+static inline bool transformIsSimple(const QTransform& transform)
+{
+    QTransform::TransformationType type = transform.type();
+    if (type == QTransform::TxNone || type == QTransform::TxTranslate) {
+        return true;
+    } else if (type == QTransform::TxScale) {
+        // Check for 0 and 180 degree rotations.
+        // (0 might happen after 4 rotations of 90 degrees).
+        qreal m11 = transform.m11();
+        qreal m12 = transform.m12();
+        qreal m21 = transform.m21();
+        qreal m22 = transform.m22();
+        if (m12 == 0.0f && m21 == 0.0f) {
+            if (m11 == 1.0f && m22 == 1.0f)
+                return true; // 0 degrees
+            else if (m11 == -1.0f && m22 == -1.0f)
+                return true; // 180 degrees.
+            if(m11 == 1.0f && m22 == -1.0f)
+                return true; // 0 degrees inverted y.
+            else if(m11 == -1.0f && m22 == 1.0f)
+                return true; // 180 degrees inverted y.
+        }
+    } else if (type == QTransform::TxRotate) {
+        // Check for 90, and 270 degree rotations.
+        qreal m11 = transform.m11();
+        qreal m12 = transform.m12();
+        qreal m21 = transform.m21();
+        qreal m22 = transform.m22();
+        if (m11 == 0.0f && m22 == 0.0f) {
+            if (m12 == 1.0f && m21 == -1.0f)
+                return true; // 90 degrees.
+            else if (m12 == -1.0f && m21 == 1.0f)
+                return true; // 270 degrees.
+            else if (m12 == -1.0f && m21 == -1.0f)
+                return true; // 90 degrees inverted y.
+            else if (m12 == 1.0f && m21 == 1.0f)
+                return true; // 270 degrees inverted y.
+        }
+    }
+    return false;
+}
+
 Q_DECL_IMPORT extern bool qt_scaleForTransform(const QTransform &transform, qreal *scale);
 
 void QVGPaintEnginePrivate::updateTransform(QPaintDevice *pdev)
 {
     VGfloat devh = pdev->height();
 
+    simpleTransform = transformIsSimple(transform);
+
     // Construct the VG transform by combining the Qt transform with
     // the following viewport transformation:
     //        | 1  0  0   |
@@ -552,9 +602,9 @@ void QVGPaintEnginePrivate::updateTransform(QPaintDevice *pdev)
         // so we will have to convert the co-ordinates ourselves.
         // Change the matrix to just the viewport transformation.
         pathTransform = viewport;
-        simpleTransform = false;
+        affineTransform = false;
     } else {
-        simpleTransform = true;
+        affineTransform = true;
     }
     pathTransformSet = false;
 
@@ -583,7 +633,7 @@ VGPath QVGPaintEnginePrivate::vectorPathToVGPath(const QVectorPath& path)
     // Size is sufficient segments for drawRoundedRect() paths.
     QVarLengthArray<VGubyte, 20> segments;
 
-    if (sizeof(qreal) == sizeof(VGfloat) && elements && simpleTransform) {
+    if (sizeof(qreal) == sizeof(VGfloat) && elements && affineTransform) {
         // If Qt was compiled with qreal the same size as VGfloat,
         // then convert the segment types and use the incoming
         // points array directly.
@@ -618,7 +668,7 @@ VGPath QVGPaintEnginePrivate::vectorPathToVGPath(const QVectorPath& path)
     int curvePos = 0;
     QPointF temp;
 
-    if (elements && simpleTransform) {
+    if (elements && affineTransform) {
         // Convert the members of the element array.
         for (int i = 0; i < count; ++i) {
             switch (elements[i]) {
@@ -662,7 +712,7 @@ VGPath QVGPaintEnginePrivate::vectorPathToVGPath(const QVectorPath& path)
             }
             points += 2;
         }
-    } else if (elements && !simpleTransform) {
+    } else if (elements && !affineTransform) {
         // Convert the members of the element array after applying the
         // current transform to the path locally.
         for (int i = 0; i < count; ++i) {
@@ -711,7 +761,7 @@ VGPath QVGPaintEnginePrivate::vectorPathToVGPath(const QVectorPath& path)
             }
             points += 2;
         }
-    } else if (count > 0 && simpleTransform) {
+    } else if (count > 0 && affineTransform) {
         // If there is no element array, then the path is assumed
         // to be a MoveTo followed by several LineTo's.
         coords.append(points[0]);
@@ -724,7 +774,7 @@ VGPath QVGPaintEnginePrivate::vectorPathToVGPath(const QVectorPath& path)
             segments.append(VG_LINE_TO_ABS);
             --count;
         }
-    } else if (count > 0 && !simpleTransform) {
+    } else if (count > 0 && !affineTransform) {
         // Convert a simple path, and apply the transform locally.
         temp = transform.map(QPointF(points[0], points[1]));
         coords.append(temp.x());
@@ -785,7 +835,7 @@ VGPath QVGPaintEnginePrivate::painterPathToVGPath(const QPainterPath& path)
     bool haveStart = false;
     bool haveEnd = false;
 
-    if (simpleTransform) {
+    if (affineTransform) {
         // Convert the members of the element array.
         for (int i = 0; i < count; ++i) {
             switch (elements[i].type) {
@@ -1560,36 +1610,6 @@ void QVGPaintEngine::stroke(const QVectorPath &path, const QPen &pen)
     vgDestroyPath(vgpath);
 }
 
-// Determine if a co-ordinate transform is simple enough to allow
-// rectangle-based clipping with vgMask().  Simple transforms most
-// often result from origin translations.
-static inline bool clipTransformIsSimple(const QTransform& transform)
-{
-    QTransform::TransformationType type = transform.type();
-    if (type == QTransform::TxNone || type == QTransform::TxTranslate)
-        return true;
-    if (type == QTransform::TxRotate) {
-        // Check for 0, 90, 180, and 270 degree rotations.
-        // (0 might happen after 4 rotations of 90 degrees).
-        qreal m11 = transform.m11();
-        qreal m12 = transform.m12();
-        qreal m21 = transform.m21();
-        qreal m22 = transform.m22();
-        if (m11 == 0.0f && m22 == 0.0f) {
-            if (m12 == 1.0f && m21 == -1.0f)
-                return true;    // 90 degrees.
-            else if (m12 == -1.0f && m21 == 1.0f)
-                return true;    // 270 degrees.
-        } else if (m12 == 0.0f && m21 == 0.0f) {
-            if (m11 == -1.0f && m22 == -1.0f)
-                return true;    // 180 degrees.
-            else if (m11 == 1.0f && m22 == 1.0f)
-                return true;    // 0 degrees.
-        }
-    }
-    return false;
-}
-
 #if defined(QVG_SCISSOR_CLIP)
 
 void QVGPaintEngine::clip(const QVectorPath &path, Qt::ClipOperation op)
@@ -1607,7 +1627,7 @@ void QVGPaintEngine::clip(const QVectorPath &path, Qt::ClipOperation op)
 
     // We aren't using masking, so handle simple QRectF's only.
     if (path.shape() == QVectorPath::RectangleHint &&
-            path.elementCount() == 4 && clipTransformIsSimple(d->transform)) {
+            path.elementCount() == 4 && d->simpleTransform) {
         // Clipping region that resulted from QPainter::setClipRect(QRectF).
         // Convert it into a QRect and apply.
         const qreal *points = path.points();
@@ -1757,7 +1777,7 @@ void QVGPaintEngine::clip(const QVectorPath &path, Qt::ClipOperation op)
 
     // We don't have vgRenderToMask(), so handle simple QRectF's only.
     if (path.shape() == QVectorPath::RectangleHint &&
-            path.elementCount() == 4 && clipTransformIsSimple(d->transform)) {
+            path.elementCount() == 4 && d->simpleTransform) {
         // Clipping region that resulted from QPainter::setClipRect(QRectF).
         // Convert it into a QRect and apply.
         const qreal *points = path.points();
@@ -1809,7 +1829,7 @@ void QVGPaintEngine::clip(const QRect &rect, Qt::ClipOperation op)
     d->dirty |= QPaintEngine::DirtyClipRegion;
 
     // If we have a non-simple transform, then use path-based clipping.
-    if (op != Qt::NoClip && !clipTransformIsSimple(d->transform)) {
+    if (op != Qt::NoClip && !d->simpleTransform) {
         QPaintEngineEx::clip(rect, op);
         return;
     }
@@ -1928,7 +1948,7 @@ void QVGPaintEngine::clip(const QRegion &region, Qt::ClipOperation op)
     d->dirty |= QPaintEngine::DirtyClipRegion;
 
     // If we have a non-simple transform, then use path-based clipping.
-    if (op != Qt::NoClip && !clipTransformIsSimple(d->transform)) {
+    if (op != Qt::NoClip && !d->simpleTransform) {
         QPaintEngineEx::clip(region, op);
         return;
     }
@@ -2505,14 +2525,14 @@ void QVGPaintEngine::fillRect(const QRectF &rect, const QBrush &brush)
 
     // Check to see if we can use vgClear() for faster filling.
     if (brush.style() == Qt::SolidPattern && brush.isOpaque() &&
-            clipTransformIsSimple(d->transform) && d->opacity == 1.0f &&
+            d->simpleTransform && d->opacity == 1.0f &&
             clearRect(rect, brush.color())) {
         return;
     }
 
 #if !defined(QVG_NO_MODIFY_PATH)
     VGfloat coords[8];
-    if (d->simpleTransform) {
+    if (d->affineTransform) {
         coords[0] = rect.x();
         coords[1] = rect.y();
         coords[2] = rect.x() + rect.width();
@@ -2547,14 +2567,14 @@ void QVGPaintEngine::fillRect(const QRectF &rect, const QColor &color)
     Q_D(QVGPaintEngine);
 
     // Check to see if we can use vgClear() for faster filling.
-    if (clipTransformIsSimple(d->transform) && d->opacity == 1.0f && color.alpha() == 255 &&
+    if (d->simpleTransform && d->opacity == 1.0f && color.alpha() == 255 &&
             clearRect(rect, color)) {
         return;
     }
 
 #if !defined(QVG_NO_MODIFY_PATH)
     VGfloat coords[8];
-    if (d->simpleTransform) {
+    if (d->affineTransform) {
         coords[0] = rect.x();
         coords[1] = rect.y();
         coords[2] = rect.x() + rect.width();
@@ -2587,7 +2607,7 @@ void QVGPaintEngine::fillRect(const QRectF &rect, const QColor &color)
 void QVGPaintEngine::drawRoundedRect(const QRectF &rect, qreal xrad, qreal yrad, Qt::SizeMode mode)
 {
     Q_D(QVGPaintEngine);
-    if (d->simpleTransform) {
+    if (d->affineTransform) {
         QVGPainterState *s = state();
         VGPath vgpath = d->roundedRectPath(rect, xrad, yrad, mode);
         d->draw(vgpath, s->pen, s->brush);
@@ -2606,7 +2626,7 @@ void QVGPaintEngine::drawRects(const QRect *rects, int rectCount)
     QVGPainterState *s = state();
     for (int i = 0; i < rectCount; ++i, ++rects) {
         VGfloat coords[8];
-        if (d->simpleTransform) {
+        if (d->affineTransform) {
             coords[0] = rects->x();
             coords[1] = rects->y();
             coords[2] = rects->x() + rects->width();
@@ -2647,7 +2667,7 @@ void QVGPaintEngine::drawRects(const QRectF *rects, int rectCount)
     QVGPainterState *s = state();
     for (int i = 0; i < rectCount; ++i, ++rects) {
         VGfloat coords[8];
-        if (d->simpleTransform) {
+        if (d->affineTransform) {
             coords[0] = rects->x();
             coords[1] = rects->y();
             coords[2] = rects->x() + rects->width();
@@ -2685,7 +2705,7 @@ void QVGPaintEngine::drawLines(const QLine *lines, int lineCount)
     QVGPainterState *s = state();
     for (int i = 0; i < lineCount; ++i, ++lines) {
         VGfloat coords[4];
-        if (d->simpleTransform) {
+        if (d->affineTransform) {
             coords[0] = lines->x1();
             coords[1] = lines->y1();
             coords[2] = lines->x2();
@@ -2713,7 +2733,7 @@ void QVGPaintEngine::drawLines(const QLineF *lines, int lineCount)
     QVGPainterState *s = state();
     for (int i = 0; i < lineCount; ++i, ++lines) {
         VGfloat coords[4];
-        if (d->simpleTransform) {
+        if (d->affineTransform) {
             coords[0] = lines->x1();
             coords[1] = lines->y1();
             coords[2] = lines->x2();
@@ -2739,7 +2759,7 @@ void QVGPaintEngine::drawEllipse(const QRectF &r)
     // Based on the description of vguEllipse() in the OpenVG specification.
     // We don't use vguEllipse(), to avoid unnecessary library dependencies.
     Q_D(QVGPaintEngine);
-    if (d->simpleTransform) {
+    if (d->affineTransform) {
         QVGPainterState *s = state();
         VGPath path = vgCreatePath(VG_PATH_FORMAT_STANDARD,
                                    VG_PATH_DATATYPE_F,
@@ -2812,7 +2832,7 @@ void QVGPaintEngine::drawPoints(const QPointF *points, int pointCount)
 
     for (int i = 0; i < pointCount; ++i, ++points) {
         VGfloat coords[4];
-        if (d->simpleTransform) {
+        if (d->affineTransform) {
             coords[0] = points->x();
             coords[1] = points->y();
             coords[2] = coords[0];
@@ -2846,7 +2866,7 @@ void QVGPaintEngine::drawPoints(const QPoint *points, int pointCount)
 
     for (int i = 0; i < pointCount; ++i, ++points) {
         VGfloat coords[4];
-        if (d->simpleTransform) {
+        if (d->affineTransform) {
             coords[0] = points->x();
             coords[1] = points->y();
             coords[2] = coords[0];
@@ -2880,7 +2900,7 @@ void QVGPaintEngine::drawPolygon(const QPointF *points, int pointCount, PolygonD
     QVarLengthArray<VGfloat, 16> coords;
     QVarLengthArray<VGubyte, 10> segments;
     for (int i = 0; i < pointCount; ++i, ++points) {
-        if (d->simpleTransform) {
+        if (d->affineTransform) {
             coords.append(points->x());
             coords.append(points->y());
         } else {
@@ -2927,7 +2947,7 @@ void QVGPaintEngine::drawPolygon(const QPoint *points, int pointCount, PolygonDr
     QVarLengthArray<VGfloat, 16> coords;
     QVarLengthArray<VGubyte, 10> segments;
     for (int i = 0; i < pointCount; ++i, ++points) {
-        if (d->simpleTransform) {
+        if (d->affineTransform) {
             coords.append(points->x());
             coords.append(points->y());
         } else {
@@ -2962,7 +2982,7 @@ void QVGPaintEngine::drawPolygon(const QPoint *points, int pointCount, PolygonDr
 
 void QVGPaintEnginePrivate::setImageOptions()
 {
-    if (opacity != 1.0f && simpleTransform) {
+    if (opacity != 1.0f && affineTransform) {
         if (opacity != paintOpacity) {
             VGfloat values[4];
             values[0] = 1.0f;
@@ -3009,7 +3029,10 @@ static void drawVGImage(QVGPaintEnginePrivate *d,
     QTransform transform(d->imageTransform);
     VGfloat scaleX = sr.width() == 0.0f ? 0.0f : r.width() / sr.width();
     VGfloat scaleY = sr.height() == 0.0f ? 0.0f : r.height() / sr.height();
-    transform.translate(r.x(), r.y());
+    if (d->simpleTransform)
+        transform.translate(qRound(r.x()), qRound(r.y()));
+    else
+        transform.translate(r.x(), r.y());
     transform.scale(scaleX, scaleY);
     d->setTransform(VG_MATRIX_IMAGE_USER_TO_SURFACE, transform);
 
@@ -3027,7 +3050,10 @@ static void drawVGImage(QVGPaintEnginePrivate *d,
         return;
 
     QTransform transform(d->imageTransform);
-    transform.translate(pos.x(), pos.y());
+    if(d->simpleTransform)
+        transform.translate(qRound(pos.x()), qRound(pos.y()));
+    else
+        transform.translate(pos.x(), pos.y());
     d->setTransform(VG_MATRIX_IMAGE_USER_TO_SURFACE, transform);
 
     d->setImageOptions();
@@ -3070,7 +3096,7 @@ void QVGPaintEngine::drawPixmap(const QRectF &r, const QPixmap &pm, const QRectF
         QVGPixmapData *vgpd = static_cast<QVGPixmapData *>(pd);
         if (!vgpd->isValid())
             return;
-        if (d->simpleTransform)
+        if (d->affineTransform)
             drawVGImage(d, r, vgpd->toVGImage(), vgpd->size(), sr);
         else
             drawVGImage(d, r, vgpd->toVGImage(d->opacity), vgpd->size(), sr);
@@ -3089,7 +3115,7 @@ void QVGPaintEngine::drawPixmap(const QPointF &pos, const QPixmap &pm)
         QVGPixmapData *vgpd = static_cast<QVGPixmapData *>(pd);
         if (!vgpd->isValid())
             return;
-        if (d->simpleTransform)
+        if (d->affineTransform)
             drawVGImage(d, pos, vgpd->toVGImage());
         else
             drawVGImage(d, pos, vgpd->toVGImage(d->opacity));
@@ -3104,7 +3130,7 @@ void QVGPaintEngine::drawImage
 {
     Q_D(QVGPaintEngine);
     VGImage vgImg;
-    if (d->simpleTransform || d->opacity == 1.0f)
+    if (d->affineTransform || d->opacity == 1.0f)
         vgImg = toVGImageSubRect(image, sr.toRect(), flags);
     else
         vgImg = toVGImageWithOpacitySubRect(image, d->opacity, sr.toRect());
@@ -3127,7 +3153,7 @@ void QVGPaintEngine::drawImage(const QPointF &pos, const QImage &image)
 {
     Q_D(QVGPaintEngine);
     VGImage vgImg;
-    if (d->simpleTransform || d->opacity == 1.0f)
+    if (d->affineTransform || d->opacity == 1.0f)
         vgImg = toVGImage(image);
     else
         vgImg = toVGImageWithOpacity(image, d->opacity);
@@ -3160,7 +3186,7 @@ void QVGPaintEngine::drawPixmapFragments(const QPainter::PixmapFragment *drawing
     QPixmapData *pd = pixmap.pixmapData();
     if (!pd)
         return; // null QPixmap
-    if (pd->classId() != QPixmapData::OpenVGClass || !d->simpleTransform) {
+    if (pd->classId() != QPixmapData::OpenVGClass || !d->affineTransform) {
         QPaintEngineEx::drawPixmapFragments(drawingData, dataCount, pixmap, hints);
         return;
     }
@@ -3385,7 +3411,7 @@ void QVGPaintEngine::drawTextItem(const QPointF &p, const QTextItem &textItem)
 
     // If we are not using a simple transform, then fall back
     // to the default Qt path stroking algorithm.
-    if (!d->simpleTransform) {
+    if (!d->affineTransform) {
         QPaintEngineEx::drawTextItem(p, textItem);
         return;
     }