In computer graphics, quad buffering is the act of using four areas of memory to render a scene, with one of the buffers being the frame that is currently being shown on the display device. The term also has a more specific connotation, and is used to describe double buffering as applied to stereoscopic displays, in which there are two buffers for the right eye and two buffers for the left eye, with one being displayed for each eye at any given time. The use of quad buffering increased in popularity as three-dimensional (3D) display hardware started to become more common and eventually became supported by a variety of different graphics cards. Depending on the type of 3D hardware being used, the buffers could both be projected onto a single screen so special glasses can be used to view the 3D effect, or each of the buffers can be outputted to a different display device, such as a head-mounted display with independent projections for each eye.
The idea behind quad buffering is similar to double buffering, except that two independent sets of buffers are used. While one buffer is being displayed, the second buffer has the current scene rendered to it. When the next frame needs to be displayed, the buffers are switched and the next frame is drawn onto the buffer that is not being displayed. This helps to make animation and movement appear very smooth to the viewer by keeping the framerate as consistent as possible.
With quad buffering, double buffering is performed for each eye. The 3D scene being used must be rendered twice from two separate angles into two separate buffers. The buffers are independent of each other, so each can be displayed as needed by the hardware used for each eye, potentially granting the ability to render and display each of the frames at different rates for each eye.
Stereoscopic rendering through quad buffering can be used to provide a 3D view of a scene through a variety of hardware-implemented methods. It also is important for applications that are designed to play certain types of media, because some video formats use 3D techniques, meaning that quad buffering becomes a necessary tool to display the video correctly. In certain instances, the use of quad buffering and stereoscopic rendering still requires special display hardware and might create an image that is unrecognizable on standard two-dimensional (2D) monitors.
