Add QQuickPathItem and its backend infra

The generic backend uses the triangulator from QtGui, but is in
fact OpenGL-only for now due to materials.

The NVPR backend uses GL_NV_path_rendering on NVIDIA hardware with
OpenGL 4.3+ or OpenGL ES 3.1+.

The software backend simply uses QPainter.

With the generic backend each PathItem is backed by a non-visual root node
and 0, 1 or 2 child geometry nodes, depending on the presence of visible
stroking and filling. The potentially expensive triangulation happens on
updatePolish(), on the gui thread. This is proven to provide much smoother
results when compared to doing the geometry generation on the render thread
in updatePaintNode(), in particular on power-limited embedded devices.

The NVPR backend uses a QSGRenderNode in DepthAware mode so that the batch
renderer can continue to rely on the depth buffer and use opaque batches.
Due to not relying on slow CPU-side triangulation, this backend uses 5-10
times less CPU, even when properties of the path or its elements are
animated.

The path itself is specified with the PathView's Path, PathLine, PathArc,
PathQuad, etc. types. This allows for consistency with PathView and the
2D Canvas and avoids a naming mess in the API. However, there won't be a
100% symmetry: backends like NVPR will not rely on QPainterPath but process
the path elements on their own (as QPainterPath is essentially useless with
these APIs), which can lead to differences in the supported path elements.

The supported common set is currently Move, Line, Quad, Cubic, Arc.

The patch introduces PathMove, which is essentially PathLine but maps to
moveTo instead of lineTo. More types may get added later (e.g. NVPR can do
a wide variety of optimized rounded rects, but this requires directly
specifying a GL_ROUNDED_RECTx_NV command, thus neededing a dedicated Path
type on our side too)

For filling with gradients only linear gradients are supported at the
moment.

In addition to the declarative API, a more lightweight, QObject-less
JS-callable API should be considered as well for the future.

Change-Id: I335ad64b425ee279505d60e3e57ac6841e1cbd24
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 67 insertions, 3 deletions

diff --git a/src/quick/util/qquickpath.cpp b/src/quick/util/qquickpath.cpp
index 25a4433a9b..a6fa21d696 100644
--- a/src/quick/util/qquickpath.cpp
+++ b/src/quick/util/qquickpath.cpp
@@ -68,7 +68,7 @@ QT_BEGIN_NAMESPACE
     \instantiates QQuickPath
     \inqmlmodule QtQuick
     \ingroup qtquick-animation-paths
-    \brief Defines a path for use by \l PathView
+    \brief Defines a path for use by \l PathView and \l PathItem
 
     A Path is composed of one or more path segments - PathLine, PathQuad,
     PathCubic, PathArc, PathCurve, PathSvg.
@@ -79,7 +79,7 @@ QT_BEGIN_NAMESPACE
     PathAttribute allows named attributes with values to be defined
     along the path.
 
-    \sa PathView, PathAttribute, PathPercent, PathLine, PathQuad, PathCubic, PathArc, PathCurve, PathSvg
+    \sa PathView, PathItem, PathAttribute, PathPercent, PathLine, PathMove, PathQuad, PathCubic, PathArc, PathCurve, PathSvg
 */
 QQuickPath::QQuickPath(QObject *parent)
  : QObject(*(new QQuickPathPrivate), parent)
@@ -1017,7 +1017,7 @@ void QQuickPathAttribute::setValue(qreal value)
     }
     \endqml
 
-    \sa Path, PathQuad, PathCubic, PathArc, PathCurve, PathSvg
+    \sa Path, PathQuad, PathCubic, PathArc, PathCurve, PathSvg, PathMove
 */
 
 /*!
@@ -1060,6 +1060,66 @@ void QQuickPathLine::addToPath(QPainterPath &path, const QQuickPathData &data)
 /****************************************************************************/
 
 /*!
+    \qmltype PathMove
+    \instantiates QQuickPathMove
+    \inqmlmodule QtQuick
+    \ingroup qtquick-animation-paths
+    \brief Moves the Path's position
+
+    While not relevant with PathView, for Path elements used with PathItem it
+    is important to distinguish between the operations of drawing a straight
+    line and moving the path position without drawing anything.
+
+    \note PathMove should not be used in a Path associated with a PathView. Use
+    PathLine instead.
+
+    The example below creates a path consisting of two horizontal lines with
+    some empty space between them. All three segments have a width of 100:
+
+    \qml
+    Path {
+        startX: 0; startY: 100
+        PathLine { relativeX: 100; y: 100 }
+        PathMove { relativeX: 100; y: 100 }
+        PathLine { relativeX: 100; y: 100 }
+    }
+    \endqml
+
+    \sa Path, PathQuad, PathCubic, PathArc, PathCurve, PathSvg, PathLine
+*/
+
+/*!
+    \qmlproperty real QtQuick::PathMove::x
+    \qmlproperty real QtQuick::PathMove::y
+
+    Defines the position to move to.
+
+    \sa relativeX, relativeY
+*/
+
+/*!
+    \qmlproperty real QtQuick::PathMove::relativeX
+    \qmlproperty real QtQuick::PathMove::relativeY
+
+    Defines the position to move to relative to its start.
+
+    If both a relative and absolute end position are specified for a single axis, the relative
+    position will be used.
+
+    Relative and absolute positions can be mixed, for example it is valid to set a relative x
+    and an absolute y.
+
+    \sa x, y
+*/
+
+void QQuickPathMove::addToPath(QPainterPath &path, const QQuickPathData &data)
+{
+    path.moveTo(positionForCurve(data, path.currentPosition()));
+}
+
+/****************************************************************************/
+
+/*!
     \qmltype PathQuad
     \instantiates QQuickPathQuad
     \inqmlmodule QtQuick
@@ -1655,6 +1715,7 @@ void QQuickPathArc::setRadiusX(qreal radius)
 
     _radiusX = radius;
     emit radiusXChanged();
+    emit changed();
 }
 
 qreal QQuickPathArc::radiusY() const
@@ -1669,6 +1730,7 @@ void QQuickPathArc::setRadiusY(qreal radius)
 
     _radiusY = radius;
     emit radiusYChanged();
+    emit changed();
 }
 
 /*!
@@ -1702,6 +1764,7 @@ void QQuickPathArc::setUseLargeArc(bool largeArc)
 
     _useLargeArc = largeArc;
     emit useLargeArcChanged();
+    emit changed();
 }
 
 /*!
@@ -1733,6 +1796,7 @@ void QQuickPathArc::setDirection(ArcDirection direction)
 
     _direction = direction;
     emit directionChanged();
+    emit changed();
 }
 
 void QQuickPathArc::addToPath(QPainterPath &path, const QQuickPathData &data)