QSGRenderNode Class

The QSGRenderNode class represents a set of custom rendering commands targeting the graphics API that is in use by the scenegraph. More...

Header: #include <QSGRenderNode>
qmake: QT += quick
Since: Qt 5.8
Inherits: QSGNode

This class was introduced in Qt 5.8.

Public Types

enum RenderingFlag { BoundedRectRendering, DepthAwareRendering, OpaqueRendering }
flags RenderingFlags
enum StateFlag { DepthState, StencilState, ScissorState, ColorState, ..., RenderTargetState }
flags StateFlags

Public Functions

virtual ~QSGRenderNode() override
virtual QSGRenderNode::StateFlags changedStates() const
const QSGClipNode *clipList() const
virtual QSGRenderNode::RenderingFlags flags() const
qreal inheritedOpacity() const
const QMatrix4x4 *matrix() const
virtual QRectF rect() const
virtual void releaseResources()
  • 10 public functions inherited from QSGNode

Detailed Description

Member Type Documentation

enum QSGRenderNode::RenderingFlag
flags QSGRenderNode::RenderingFlags

Possible values for the bitmask returned from flags().

QSGRenderNode::BoundedRectRendering0x01Indicates that the implementation of render() does not render outside the area reported from rect() in item coordinates. Such node implementations can lead to more efficient rendering, depending on the scenegraph backend. For example, the software backend can continue to use the more optimal partial update path when all render nodes in the scene have this flag set.
QSGRenderNode::DepthAwareRendering0x02Indicates that the implementations of render() conforms to scenegraph expectations by only generating a Z value of 0 in scene coordinates which is then transformed by the matrices retrieved from RenderState::projectionMatrix() and matrix(), as described in the notes for render(). Such node implementations can lead to more efficient rendering, depending on the scenegraph backend. For example, the batching OpenGL renderer can continue to use a more optimal path when all render nodes in the scene have this flag set.
QSGRenderNode::OpaqueRendering0x04Indicates that the implementation of render() writes out opaque pixels for the entire area reported from rect(). By default the renderers must assume that render() can also output semi or fully transparent pixels. Setting this flag can improve performance in some cases.

The RenderingFlags type is a typedef for QFlags<RenderingFlag>. It stores an OR combination of RenderingFlag values.

See also render() and rect().

enum QSGRenderNode::StateFlag
flags QSGRenderNode::StateFlags

This enum is a bit mask identifying several states.

QSGRenderNode::ViewportState0x40View poirt
QSGRenderNode::RenderTargetState0x80Render target

The StateFlags type is a typedef for QFlags<StateFlag>. It stores an OR combination of StateFlag values.

Member Function Documentation

[override virtual] QSGRenderNode::~QSGRenderNode()

Destructs the render node. Derived classes are expected to perform cleanup similar to releaseResources() in here.

When a low-level graphics API is in use, the scenegraph will make sure there is a CPU-side wait for the GPU to complete all work submitted to the scenegraph's graphics command queue before the scenegraph's nodes are deleted. Therefore there is no need to issue additional waits here, unless the render() implementation is using additional command queues.

See also releaseResources().

[virtual] QSGRenderNode::StateFlags QSGRenderNode::changedStates() const

This function should return a mask where each bit represents graphics states changed by the render() function:

The function is called by the renderer so it can reset the states after rendering this node. This makes the implementation of render() simpler since it does not have to query and restore these states.

The default implementation returns 0, meaning no relevant state was changed in render().

With APIs other than OpenGL the relevant states are only those that are set via the command list (for example, OMSetRenderTargets, RSSetViewports, RSSetScissorRects, OMSetBlendFactor, OMSetStencilRef in case of D3D12), and only when such commands were added to the scenegraph's command list queried via the QSGRendererInterface::CommandList resource enum. States set in pipeline state objects do not need to be reported here. Similarly, draw call related settings (root signature, descriptor heaps, etc.) are always set again by the scenegraph so render() can freely change them.

The software backend exposes its QPainter and saves and restores before and after invoking render(). Therefore reporting any changed states from here is not necessary.

Note: This function may be called before render().

const QSGClipNode *QSGRenderNode::clipList() const

Returns the current clip list.

[virtual] QSGRenderNode::RenderingFlags QSGRenderNode::flags() const

Returns flags describing the behavior of this render node.

The default implementation returns 0.

See also RenderingFlag and rect().

qreal QSGRenderNode::inheritedOpacity() const

Returns the current effective opacity.

const QMatrix4x4 *QSGRenderNode::matrix() const

Returns pointer to the current model-view matrix.

[virtual] QRectF QSGRenderNode::rect() const

Returns the bounding rectangle in item coordinates for the area render() touches. The value is only in use when flags() includes BoundedRectRendering, ignored otherwise.

Reporting the rectangle in combination with BoundedRectRendering is particularly important with the software backend because otherwise having a rendernode in the scene would trigger fullscreen updates, skipping all partial update optimizations.

For rendernodes covering the entire area of a corresponding QQuickItem the return value will be (0, 0, item->width(), item->height()).

Note: Nodes are also free to render outside the boundaries specified by the item's width and height, since the scenegraph nodes are not bounded by the QQuickItem geometry, as long as this is reported correctly from this function.

See also flags().

[virtual] void QSGRenderNode::releaseResources()

This function is called when all custom graphics resources allocated by this node have to be freed immediately. In case the node does not directly allocate graphics resources (buffers, textures, render targets, fences, etc.) through the graphics API that is in use, there is nothing to do here.

Failing to release all custom resources can lead to incorrect behavior in graphics device loss scenarios on some systems since subsequent reinitialization of the graphics system may fail.

Note: Some scenegraph backends may choose not to call this function. Therefore it is expected that QSGRenderNode implementations perform cleanup both in their destructor and in releaseResources().

Unlike with the destructor, it is expected that render() can reinitialize all resources it needs when called after a call to releaseResources().

With OpenGL, the scenegraph's OpenGL context will be current both when calling the destructor and this function.

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