class Renderer#



Virtual methods#


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Detailed Description#

The Renderer class is used to implement the rendering logic of a QQuickFramebufferObject .


Constructs a new renderer.

This function is called during the scene graph sync phase when the GUI thread is blocked.



Return type:


This function is called when a new FBO is needed. This happens on the initial frame. If textureFollowsItemSize is set to true, it is called again every time the dimensions of the item changes.

The returned FBO can have any attachment. If the QOpenGLFramebufferObjectFormat indicates that the FBO should be multisampled, the internal implementation of the Renderer will allocate a second FBO and blit the multisampled FBO into the FBO used to display the texture.


Some hardware has issues with small FBO sizes. size takes that into account, so be cautious when overriding the size with a fixed size. A minimal size of 64x64 should always work.


size takes the device pixel ratio into account, meaning that it is already multiplied by the correct scale factor. When moving the window containing the QQuickFramebufferObject item to a screen with different settings, the FBO is automatically recreated and this function is invoked with the correct size.

Return type:


Returns the framebuffer object currently being rendered to.


Call this function during synchronize() to invalidate the current FBO. This will result in a new FBO being created with createFramebufferObject() .

abstract render()#

This function is called when the FBO should be rendered into. The framebuffer is bound at this point and the glViewport has been set up to match the FBO size.

The FBO will be automatically unbound after the function returns.


Do not assume that the OpenGL state is all set to the defaults when this function is invoked, or that it is maintained between calls. Both the Qt Quick renderer and the custom rendering code uses the same OpenGL context. This means that the state might have been modified by Quick before invoking this function.


It is recommended to call resetOpenGLState() before returning. This resets OpenGL state used by the Qt Quick renderer and thus avoids interference from the state changes made by the rendering code in this function.



This function is called as a result of update() .

Use this function to update the renderer with changes that have occurred in the item. item is the item that instantiated this renderer. The function is called once before the FBO is created.

For instance, if the item has a color property which is controlled by QML, one should call update() and use synchronize() to copy the new color into the renderer so that it can be used to render the next frame.

This function is the only place when it is safe for the renderer and the item to read and write each others members.


Call this function when the FBO should be rendered again.

This function can be called from render() to force the FBO to be rendered again before the next frame.


This function should be used from inside the renderer. To update the item on the GUI thread, use update() .