Shape QML Type

Renders a path. More...

Import Statement: import QtQuick.Shapes 1.6


Inherited By:

EllipseShape and MaskShape


Detailed Description

Renders a path by triangulating geometry from a QPainterPath.

This approach is different from rendering shapes via QQuickPaintedItem or the 2D Canvas because the path never gets rasterized in software. Therefore Shape is suitable for creating shapes spreading over larger areas of the screen, avoiding the performance penalty for texture uploads or framebuffer blits. In addition, the declarative API allows manipulating, binding to, and even animating the path element properties like starting and ending position, the control points, and so on.

The types for specifying path elements are shared between PathView and Shape. However, not all Shape implementations support all path element types, while some may not make sense for PathView. Shape's currently supported subset is: PathMove, PathLine, PathQuad, PathCubic, PathArc, PathText and PathSvg.

See Path for a detailed overview of the supported path elements.

Shape {
    width: 200
    height: 150
    anchors.centerIn: parent
    ShapePath {
        strokeWidth: 4
        strokeColor: "red"
        fillGradient: LinearGradient {
            x1: 20; y1: 20
            x2: 180; y2: 130
            GradientStop { position: 0; color: "blue" }
            GradientStop { position: 0.2; color: "green" }
            GradientStop { position: 0.4; color: "red" }
            GradientStop { position: 0.6; color: "yellow" }
            GradientStop { position: 1; color: "cyan" }
        strokeStyle: ShapePath.DashLine
        dashPattern: [ 1, 4 ]
        startX: 20; startY: 20
        PathLine { x: 180; y: 130 }
        PathLine { x: 20; y: 130 }
        PathLine { x: 20; y: 20 }

Like Item, Shape also allows any visual or non-visual objects to be declared as children. ShapePath objects are handled specially. This is useful since it allows adding visual items, like Rectangle or Image, and non-visual objects, like Timer directly as children of Shape.

The following list summarizes the available Shape rendering approaches:

  • When Qt Quick is running with the default, hardware-accelerated backend (RHI), the generic shape renderer will be used. This converts the shapes into triangles which are passed to the renderer.
  • The software backend is fully supported. The path is rendered via QPainter::strokePath() and QPainter::fillPath() in this case.
  • The OpenVG backend is not currently supported.

When using Shape, it is important to be aware of potential performance implications:

  • When the application is running with the generic, triangulation-based Shape implementation, the geometry generation happens entirely on the CPU. This is potentially expensive. Changing the set of path elements, changing the properties of these elements, or changing certain properties of the Shape itself all lead to retriangulation of the affected paths on every change. Therefore, applying animation to such properties can affect performance on less powerful systems.
  • However, the data-driven, declarative nature of the Shape API often means better cacheability for the underlying CPU and GPU resources. A property change in one ShapePath will only lead to reprocessing the affected ShapePath, leaving other parts of the Shape unchanged. Therefore, a frequently changing property can still result in a lower overall system load than with imperative painting approaches (for example, QPainter).
  • At the same time, attention must be paid to the number of Shape elements in the scene. The way such a Shape item is represented in the scene graph is different from an ordinary geometry-based item, and incurs a certain cost when it comes to OpenGL state changes.
  • As a general rule, scenes should avoid using separate Shape items when it is not absolutely necessary. Prefer using one Shape item with multiple ShapePath elements over multiple Shape items.

See also Qt Quick Examples - Shapes, Path, PathMove, PathLine, PathQuad, PathCubic, PathArc, and PathSvg.

Property Documentation

asynchronous : bool

When rendererType is Shape.GeometryRenderer, the input path is triangulated on the CPU during the polishing phase of the Shape. This is potentially expensive. To offload this work to separate worker threads, set this property to true.

When enabled, making a Shape visible will not wait for the content to become available. Instead, the GUI/main thread is not blocked and the results of the path rendering are shown only when all the asynchronous work has been finished.

The default value is false.

[since 6.6] boundingRect : rect

Contains the united bounding rect of all sub paths in the shape.

This property was introduced in Qt 6.6.

[since QtQuick.Shapes 1.11] containsMode : enumeration

This property determines the definition of contains() for the Shape. It is useful in case you add Qt Quick Input Handlers and you want to react only when the mouse or touchpoint is fully inside the Shape.

Shape.BoundingRectContainsThe default implementation of QQuickItem::contains() checks only whether the given point is inside the rectangular bounding box. This is the most efficient implementation, which is why it's the default.
Shape.FillContainsCheck whether the interior (the part that would be filled if you are rendering it with fill) of any ShapePath that makes up this Shape contains the given point. The more complex and numerous ShapePaths you add, the less efficient this is to check, which can potentially slow down event delivery in your application. So it should be used with care.

One way to speed up the FillContains check is to generate an approximate outline with as few points as possible, place that in a transparent Shape on top, and add your Pointer Handlers to that, so that the containment check is cheaper during event delivery.

This property was introduced in QtQuick.Shapes 1.11.

[default] data : list<Object>

This property holds the ShapePath objects that define the contents of the Shape. It can also contain any other type of objects, since Shape, like Item, allows adding any visual or non-visual objects as children.

[since 6.6] preferredRendererType : enumeration

Requests a specific backend to use for rendering the shape. The possible values are the same as for rendererType. The default is Shape.UnknownRenderer, indicating no particular preference.

If the requested renderer type is not supported for the current Qt Quick backend, the default renderer for that backend will be used instead. This will be reflected in the rendererType when the backend is initialized.

Shape.SoftwareRenderer can currently not be selected without running the scenegraph with the software backend, in which case it will be selected regardless of the preferredRendererType.

Note: This API is considered tech preview and may change or be removed in future versions of Qt.

See rendererType for more information on the implications.

This property was introduced in Qt 6.6.

[read-only] rendererType : enumeration

This property determines which path rendering backend is active.

Shape.UnknownRendererThe renderer is unknown.
Shape.GeometryRendererThe generic, driver independent solution for GPU rendering. Uses the same CPU-based triangulation approach as QPainter's OpenGL 2 paint engine. This is the default when the RHI-based Qt Quick scenegraph backend is in use.
Shape.SoftwareRendererPure QPainter drawing using the raster paint engine. This is the default, and only, option when the Qt Quick scenegraph is running with the software backend.
Shape.CurveRendererExperimental GPU-based renderer, added as technology preview in Qt 6.6. In contrast to Shape.GeometryRenderer, curves are not approximated by short straight lines. Instead, curves are rendered using a specialized fragment shader. This improves visual quality and avoids re-tesselation performance hit when zooming. Also, Shape.CurveRenderer provides native, high-quality anti-aliasing, without the performance cost of multi- or supersampling.

By default, Shape.GeometryRenderer will be selected unless the Qt Quick scenegraph is running with the software backend. In that case, Shape.SoftwareRenderer will be used. Shape.CurveRenderer may be requested using the preferredRendererType property.

Note that Shape.CurveRenderer is currently regarded as experimental. The enum name of this renderer may change in future versions of Qt, and some shapes may render incorrectly. Among the known limitations are:

  1. Only quadratic curves are inherently supported. Cubic curves will be approximated by quadratic curves.
  2. Shapes where elements intersect are not rendered correctly. The Path.simplify property may be used to remove self-intersections from such shapes, but may incur a performance cost and reduced visual quality.
  3. Shapes that span a large numerical range, such as a long string of text, may have issues. Consider splitting these shapes into multiple ones, for instance by making a PathText for each individual word.
  4. If the shape is being rendered into a Qt Quick 3D scene, the GL_OES_standard_derivatives extension to OpenGL is required when the OpenGL RHI backend is in use (this is available by default on OpenGL ES 3 and later, but optional in OpenGL ES 2).

[read-only] status : enumeration

This property determines the status of the Shape and is relevant when Shape.asynchronous is set to true.

Shape.NullNot yet initialized.
Shape.ReadyThe Shape has finished processing.
Shape.ProcessingThe path is being processed.

vendorExtensionsEnabled : bool

This property controls the usage of non-standard OpenGL extensions.

The default value is false.

As of Qt 6.0 there are no vendor-specific rendering paths implemented.

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