QML Canvas item doesn't update more than once if the Canvas is the only non-static Item in the Scene

A Scene using Canvas, and context2D is updated by a timer, and there are no other QML items that are being updated, then the SceneGraph is never marked changed.

Updates will be applied if another window is placed on top and moved, or if a control is added to the scene and it is marks the SceneGraph changed.

I believe the issue is that the Canvas dirty flags are all cleared when it is rendered into the backing image, and the updatePaintNode code is only checking if the texture address has changed in order to determine if the scene must be rendered.

In the example below, if the Text Item (below the Canvas Item in badcanvas-good.qml) changes its contents, then the Scene is marked changed, and the Canvas updates are rendered.