Add ObjectMode coordinate mode to QGradient

The ObjectBoundingMode coordinate mode of QGradient allows specifying
the gradient coordinates relative to the object being painted. But if
the gradient brush also has a transformation, that transformation is
applied in the logical, not object, coordinate space. That behavior is
counterintuitive. However, changing it now would break existing
code. Instead, we introduce a new coordinate mode enum with the
expected behavior, and document the old one as deprecated.

This prepares to fix the bugs below in qtsvg, by making
it possible to specify the same behavior in Qt as SVG has.

[ChangeLog][QtGui][QGradient] Add ObjectMode coordinate mode
[ChangeLog][Important Behavior Changes] QDataStream version bumped up to 18 to account for changes in the serialization of QGradient.

Task-number: QTBUG-59978
Task-number: QTBUG-67995
Change-Id: I8820a2555359812f3e1a46e37d6ac2cc29a2091d
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/corelib/serialization/qdatastream.h

@@ -98,7 +98,7 @@ public:
         Qt_5_9 = Qt_5_8,
         Qt_5_10 = Qt_5_9,
         Qt_5_11 = Qt_5_10,
-        Qt_5_12 = Qt_5_11,
+        Qt_5_12 = 18,
 #if QT_VERSION >= 0x050d00
 #error Add the datastream version for this Qt version and update Qt_DefaultCompiledVersion
 #endif

src/gui/painting/qbrush.cpp

@@ -1077,7 +1077,10 @@ QDataStream &operator<<(QDataStream &s, const QBrush &b)
         s << type_as_int;
         if (s.version() >= QDataStream::Qt_4_3) {
             s << int(gradient->spread());
-            s << int(gradient->coordinateMode());
+            QGradient::CoordinateMode co_mode = gradient->coordinateMode();
+            if (s.version() < QDataStream::Qt_5_12 && co_mode == QGradient::ObjectMode)
+                co_mode = QGradient::ObjectBoundingMode;
+            s << int(co_mode);
         }
 
         if (s.version() >= QDataStream::Qt_4_5)
@@ -1562,14 +1565,19 @@ QGradientStops QGradient::stops() const
 
     \value LogicalMode This is the default mode. The gradient coordinates
     are specified logical space just like the object coordinates.
+    \value ObjectMode In this mode the gradient coordinates are
+    relative to the bounding rectangle of the object being drawn, with
+    (0,0) in the top left corner, and (1,1) in the bottom right corner
+    of the object's bounding rectangle. This value was added in Qt
+    5.12.
     \value StretchToDeviceMode In this mode the gradient coordinates
     are relative to the bounding rectangle of the paint device,
     with (0,0) in the top left corner, and (1,1) in the bottom right
     corner of the paint device.
-    \value ObjectBoundingMode In this mode the gradient coordinates are
+    \value ObjectBoundingMode This mode is the same as ObjectMode, except that
-    relative to the bounding rectangle of the object being drawn, with
+    the {QBrush::transform()} {brush transform}, if any, is applied relative to
-    (0,0) in the top left corner, and (1,1) in the bottom right corner
+    the logical space instead of the object space. This enum value is
-    of the object's bounding rectangle.
+    deprecated and should not be used in new code.
 */
 
 /*!

src/gui/painting/qbrush.h

@@ -194,7 +194,8 @@ public:
     enum CoordinateMode {
         LogicalMode,
         StretchToDeviceMode,
-        ObjectBoundingMode
+        ObjectBoundingMode,
+        ObjectMode
     };
     Q_ENUM(CoordinateMode)
 

src/gui/painting/qemulationpaintengine.cpp

@@ -74,10 +74,11 @@ QPainterState *QEmulationPaintEngine::createState(QPainterState *orig) const
 
 static inline void combineXForm(QBrush *brush, const QRectF &r)
 {
-    QTransform t = brush->transform();
+    QTransform t(r.width(), 0, 0, r.height(), r.x(), r.y());
-    t.translate(r.x(), r.y());
+    if (brush->gradient()->coordinateMode() == QGradient::ObjectMode)
-    t.scale(r.width(), r.height());
+        brush->setTransform(brush->transform() * t);
-    brush->setTransform(t);
+    else
+        brush->setTransform(t * brush->transform());
 }
 
 void QEmulationPaintEngine::fill(const QVectorPath &path, const QBrush &brush)
@@ -96,7 +97,7 @@ void QEmulationPaintEngine::fill(const QVectorPath &path, const QBrush &brush)
         if (coMode > QGradient::LogicalMode) {
             QBrush copy = brush;
             const QPaintDevice *d = real_engine->painter()->device();
-            QRectF r = (coMode == QGradient::ObjectBoundingMode) ? path.controlPointRect() : QRectF(0, 0, d->width(), d->height());
+            QRectF r = (coMode == QGradient::StretchToDeviceMode) ? QRectF(0, 0, d->width(), d->height()) : path.controlPointRect();
             combineXForm(&copy, r);
             real_engine->fill(path, copy);
             return;
@@ -132,7 +133,7 @@ void QEmulationPaintEngine::stroke(const QVectorPath &path, const QPen &pen)
         QGradient::CoordinateMode coMode = brush.gradient()->coordinateMode();
         if (coMode > QGradient::LogicalMode) {
             const QPaintDevice *d = real_engine->painter()->device();
-            QRectF r = (coMode == QGradient::ObjectBoundingMode) ? path.controlPointRect() : QRectF(0, 0, d->width(), d->height());
+            QRectF r = (coMode == QGradient::StretchToDeviceMode) ? QRectF(0, 0, d->width(), d->height()) : path.controlPointRect();
             combineXForm(&brush, r);
             copy.setBrush(brush);
             real_engine->stroke(path, copy);
@@ -174,9 +175,9 @@ void QEmulationPaintEngine::drawTextItem(const QPointF &p, const QTextItem &text
             QBrush copy = s->pen.brush();
             const QPaintDevice *d = real_engine->painter()->device();
             const QTextItemInt &ti = static_cast<const QTextItemInt &>(textItem);
-            QRectF r = (g.coordinateMode() == QGradient::ObjectBoundingMode) ?
+            QRectF r = (g.coordinateMode() == QGradient::StretchToDeviceMode) ?
-                        QRectF(p.x(), p.y() - ti.ascent.toReal(), ti.width.toReal(), (ti.ascent + ti.descent + 1).toReal()) :
+                        QRectF(0, 0, d->width(), d->height()) :
-                        QRectF(0, 0, d->width(), d->height());
+                        QRectF(p.x(), p.y() - ti.ascent.toReal(), ti.width.toReal(), (ti.ascent + ti.descent + 1).toReal());
             combineXForm(&copy, r);
             g.setCoordinateMode(QGradient::LogicalMode);
             QBrush brush(g);

src/gui/painting/qpainter.cpp

@@ -530,7 +530,10 @@ static inline QBrush stretchGradientToUserSpace(const QBrush &brush, const QRect
     g.setCoordinateMode(QGradient::LogicalMode);
 
     QBrush b(g);
-    b.setTransform(gradientToUser * b.transform());
+    if (brush.gradient()->coordinateMode() == QGradient::ObjectMode)
+        b.setTransform(b.transform() * gradientToUser);
+    else
+        b.setTransform(gradientToUser * b.transform());
     return b;
 }
 
@@ -569,7 +572,7 @@ void QPainterPrivate::drawStretchedGradient(const QPainterPath &path, DrawOperat
         } else {
             needsFill = true;
 
-            if (brushMode == QGradient::ObjectBoundingMode) {
+            if (brushMode == QGradient::ObjectBoundingMode || brushMode == QGradient::ObjectMode) {
                 Q_ASSERT(engine->hasFeature(QPaintEngine::PatternTransform));
                 boundingRect = path.boundingRect();
                 q->setBrush(stretchGradientToUserSpace(brush, boundingRect));
@@ -613,11 +616,11 @@ void QPainterPrivate::drawStretchedGradient(const QPainterPath &path, DrawOperat
                 changedBrush = true;
             }
 
-            if (penMode == QGradient::ObjectBoundingMode) {
+            if (penMode == QGradient::ObjectBoundingMode || penMode == QGradient::ObjectMode) {
                 Q_ASSERT(engine->hasFeature(QPaintEngine::PatternTransform));
 
                 // avoid computing the bounding rect twice
-                if (!needsFill || brushMode != QGradient::ObjectBoundingMode)
+                if (!needsFill || (brushMode != QGradient::ObjectBoundingMode && brushMode != QGradient::ObjectMode))
                     boundingRect = path.boundingRect();
 
                 QPen p = pen;
@@ -849,8 +852,8 @@ void QPainterPrivate::updateEmulationSpecifier(QPainterState *s)
         gradientStretch |= (brushMode == QGradient::StretchToDeviceMode);
         gradientStretch |= (penMode == QGradient::StretchToDeviceMode);
 
-        objectBoundingMode |= (brushMode == QGradient::ObjectBoundingMode);
+        objectBoundingMode |= (brushMode == QGradient::ObjectBoundingMode || brushMode == QGradient::ObjectMode);
-        objectBoundingMode |= (penMode == QGradient::ObjectBoundingMode);
+        objectBoundingMode |= (penMode == QGradient::ObjectBoundingMode || penMode == QGradient::ObjectMode);
     }
     if (gradientStretch)
         s->emulationSpecifier |= QGradient_StretchToDevice;
@@ -6857,7 +6860,8 @@ static inline bool needsResolving(const QBrush &brush)
     Qt::BrushStyle s = brush.style();
     return ((s == Qt::LinearGradientPattern || s == Qt::RadialGradientPattern ||
              s == Qt::ConicalGradientPattern) &&
-            brush.gradient()->coordinateMode() == QGradient::ObjectBoundingMode);
+            (brush.gradient()->coordinateMode() == QGradient::ObjectBoundingMode ||
+             brush.gradient()->coordinateMode() == QGradient::ObjectMode));
 }
 
 /*!

src/widgets/kernel/qwidget.cpp

@@ -2403,7 +2403,8 @@ static inline void fillRegion(QPainter *painter, const QRegion &rgn, const QBrus
 #endif
 
     } else if (brush.gradient()
-               && brush.gradient()->coordinateMode() == QGradient::ObjectBoundingMode) {
+               && (brush.gradient()->coordinateMode() == QGradient::ObjectBoundingMode
+                   || brush.gradient()->coordinateMode() == QGradient::ObjectMode)) {
         painter->save();
         painter->setClipRegion(rgn);
         painter->fillRect(0, 0, painter->device()->width(), painter->device()->height(), brush);

tests/auto/other/lancelot/paintcommands.cpp

@@ -106,7 +106,8 @@ const char *PaintCommands::spreadMethodTable[] = {
 const char *PaintCommands::coordinateMethodTable[] = {
     "LogicalMode",
     "StretchToDeviceMode",
-    "ObjectBoundingMode"
+    "ObjectBoundingMode",
+    "ObjectMode"
 };
 
 const char *PaintCommands::sizeModeTable[] = {
@@ -2394,7 +2395,7 @@ void PaintCommands::command_gradient_setSpread(QRegularExpressionMatch re)
 
 void PaintCommands::command_gradient_setCoordinateMode(QRegularExpressionMatch re)
 {
-    int coord = translateEnum(coordinateMethodTable, re.captured(1), 3);
+    int coord = translateEnum(coordinateMethodTable, re.captured(1), 4);
 
     if (m_verboseMode)
         printf(" -(lance) gradient_setCoordinateMode %d=[%s]\n", coord,

tests/auto/other/lancelot/scripts/gradientxform_object.qps

@@ -62,7 +62,22 @@ repeat_block row
 restore
 end_block block
 
+save
 translate 400 0
 brushRotate 30.0
 brushScale 1.5 .5
 repeat_block block
+restore
+
+drawText 80 400 "BRUSH XFORM, OBJECT BOUNDING MODE"
+drawText 500 400 "BRUSH XFORM, OBJECT MODE"
+
+translate 0 400
+brushTranslate 0.5 0.5
+brushRotate 180.0
+brushTranslate -0.5 -0.5
+repeat_block block
+
+translate 400 0
+gradient_setCoordinateMode ObjectMode
+repeat_block block