need an example for vulkan render on item, not on whole window (QSGRenderNode)

the example 'Hello Vulkan Triangle Example' render the triangle on whole window.

need an example render only on an item, but not whole window.

I know the Qt provided method for offscreen rendering, but paste it on the window will result performance loss.

I want to render item content direct to screen, and qt ensure the stacking item order.