Hardware overlay
In computing, hardware overlay, a type of video overlay, provides a method of rendering an image to a display screen with a dedicated memory buffer inside computer video hardware. The technique aims to improve the display of a fast-moving video image — such as a computer game, a DVD, or the signal from a TV card. Most video cards manufactured since about 1998 and most media players support hardware overlay.
The overlay is a dedicated buffer into which one app can render (typically video), without incurring the significant performance cost of checking for clipping and overlapping rendering by other apps. The framebuffer has hardware support for importing and rendering the buffer contents without going through the GPU.
Overview
The use of a hardware overlay is important for several reasons:
in a graphical user interface (GUI) operating system such as Windows, one display-device can typically display multiple applications simultaneously.
consider how a display works without a hardware overlay. When each application draws to the screen, the operating system's graphical subsystem must constantly check to ensure that the objects being drawn appear on the appropriate location on the screen, and that they don't collide with overlapping and neighboring windows. The graphical subsystem must clip objects while they are being drawn when a collision occurs. This constant checking and clipping ensures that different applications can cooperate with one another in sharing a display, but also consumes a significant proportion of computing power.
