Which windowing system for embedded linux supports hardware overlay?
Is it possible to add hardware overlay support in Qt for embedded Linux?
Qt for Embedded Linux uses Qt's own windowing system. For rendering the graphics, back-ends are used. Some of these back-ends support hardware graphics acceleration - for instance the PowerVR back-end used for high-end OMAP-based systems. Here, you can probably create overlays, but you will have to do it using Qt, as Qt takes full ownership of the screen.
Another alternative that I've used (when implemented a set-top-box functionality, i.e. UI over video) is to write a custom back-end for Qt and then equip it with additional hooks that you can use to control the overlay functionality (i.e. circumvent Qt from within your Qt application). But I guess that approach counts as a hack!