> 3. In Qt, if I overlap 52 QML rectangles like a deck of cards, does the renderer only paint the parts of the rectangles that will be visible in the viewport?

> 3. In Qt, if I overlap 52 QML rectangles like a deck of cards, does the renderer only paint the parts of the rectangles that will be visible in the viewport? I was under the impression that this was the case, but I may be misunderstanding how the Qt QML scenegraph (or whatever it is called) works in practice. Nope, QML draws everything back-to-front with overdraw. From what I can tell, there is an ability to batch things into standard forward-renderer opaque/alpha passes, but that requires setting a flag QSGRenderNode::DepthAwareRendering which no builtin nodes set, from what I can tell, so the whole thing is skipped. The core renderer code is here: http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/s... Search for m_useDepthBuffer and DepthAwareRendering and follow the trail -- the only use of the flag is from an example about raw OpenGL integration.