Qt 5.13 | Qt Quick | QML Types | Shape QML Type

Qt 5.13.2 Reference Documentation

# Shape QML Type

Renders a path. More...

Import Statement: | import QtQuick.Shapes 1.13
Since: | Qt 5.10
Inherits: | Item
Inherited By: | EllipseShape, LineShape, and MaskShape

- List of all members, including inherited members

## Properties

- asynchronous : bool
- containsMode : enumeration
- data : list<Object>
- rendererType : enumeration
- status : enumeration
- vendorExtensionsEnabled : bool

## Detailed Description

Renders a path either by generating geometry via QPainterPath and manual triangulation or by using a GPU vendor extension like `GL_NV_path_rendering`.

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, 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 running with the default, OpenGL backend of Qt Quick, both the generic, triangulation-based and the NVIDIA-specific `GL_NV_path_rendering` methods are available. By default only the generic approach is used. Setting Shape.vendorExtensionsEnabled property to `true` leads to using NV_path_rendering on NVIDIA systems, and the generic method on others.
- The `software` backend is fully supported. The path is rendered via QPainter::strokePath() and QPainter::fillPath() in this case.
- The Direct 3D 12 backend is not currently supported.
- 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).
- If animating properties other than stroke and fill colors is a must, it is recommended to target systems providing `GL_NV_path_rendering` where the cost of property changes is smaller.
- At the same time, attention must be paid to the number of Shape elements in the scene, in particular when using this special accelerated approach for `GL_NV_path_rendering`. 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`.

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.

Constant | Description
--- | ---
`Shape.BoundingRectContains` | The 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.FillContains` | Check 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.

rendererType : enumeration

This property determines which path rendering backend is active.

Constant | Description
--- | ---
`Shape.UnknownRenderer` | The renderer is unknown.
`Shape.GeometryRenderer` | The generic, driver independent solution for OpenGL. Uses the same CPU-based triangulation approach as QPainter's OpenGL 2 paint engine. This is the default on non-NVIDIA hardware when the default, OpenGL Qt Quick scenegraph backend is in use.
`Shape.NvprRenderer` | Path items are rendered by performing OpenGL calls using the `GL_NV_path_rendering` extension. This is the default on NVIDIA hardware when the default, OpenGL Qt Quick scenegraph backend is in use.
`Shape.SoftwareRenderer` | Pure 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.

status : enumeration

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

Constant | Description
--- | ---
`Shape.Null` | Not yet initialized.
`Shape.Ready` | The Shape has finished processing.
`Shape.Processing` | The path is being processed.

vendorExtensionsEnabled : bool

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

The default value is `false`.

As of Qt 5.12 Shape.NvprRenderer is disabled by default and a uniform behavior, based on triangulating the path and generating QSGGeometryNode instances, is used regardless of the graphics card and drivers. To enable using vendor-specific path rendering approaches set the value to `true`. Depending on the platform and content, this can lead to improved performance. Setting the value to `true` is safe in any case since rendering falls back to the default method when the vendor-specific approach, such as `GL_NV_path_rendering`, is not supported at run time.