![]() The geometry is defined using QSGGeometry and describes the shape or mesh of the graphical primitive. It is used to define custom graphics by defining its geometry and material. The most important node for users is the QSGGeometryNode. ![]() The nodes themselves do not contain any active drawing code nor virtual paint() function.Įven though the node tree is mostly built internally by the existing Qt Quick QML types, it is possible for users to also add complete subtrees with their own content, including subtrees that represent 3D models. The tree is built from QQuickItem types in the QML scene and internally the scene is then processed by a renderer which draws the scene. Although we refer to it as a scene graph, a more precise definition is node tree. The scene graph is composed of a number of predefined node types, each serving a dedicated purpose. For more information about the different scene graph adaptations see Scene Graph Adaptations. ![]() When using an alternative scene graph adaptation, such as, the software adaptation, not all concepts may apply. Note: Much of the information listed on this page is specific to the built-in, default behavior of the Qt Quick Scene graph. On many platforms, the scene graph will even be rendered on a dedicated render thread while the GUI thread is preparing the next frame's state. Once it has been set up, it can be manipulated and rendered independently of the state of the items. The scene graph is a graphical representation of the Item scene, an independent structure that contains enough information to render all the items. The scene graph is managed and rendered by the QQuickWindow class and custom Item types can add their graphical primitives into the scene graph through a call to QQuickItem::updatePaintNode(). The scene graph is closely tied to Qt Quick 2.0 and can not be used stand-alone. Batching and state change reduction like this can greatly improve performance on some hardware. A scene graph, on the other hand, could reorganize the primitives to render such that all backgrounds are drawn in one call, then all icons, then all the text, reducing the total amount of draw calls to only 3. Using the traditional drawing techniques, this would result in 30 draw calls and a similar amount of state changes. This opens up for a number of optimizations, such as batch rendering to minimize state changes and discarding obscured primitives.įor example, say a user-interface contains a list of ten items where each item has a background color, an icon and a text. Using a scene graph for graphics rather than the traditional imperative painting systems ( QPainter and similar), means the scene to be rendered can be retained between frames and the complete set of primitives to render is known before rendering starts. Qt Quick 2 makes use of a dedicated scene graph that is then traversed and rendered via a graphics API such as OpenGL ES, OpenGL, Vulkan, Metal, or Direct 3D.
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