Passive Display Devices

Passive stereo displays, such as head-mounted displays and auto-stereographic displays, are simpler to control than active devices. In passive displays have a separate display (or region of a single display) that is mechanically constructed so that each eye receives a different view. DirectDraw creates left and right surfaces within a single physical display surface. The display surface is scanned to the device and the device places the data into the correct mechanical location. For example, a head-mounted display might require that a single 640 × 480 display surface be treated as a side-by-side unit, composed of a 320 × 480 left and a 320 × 480 right surface. In this case, the display device would place the correct image in front of each eye.

For passive devices, there is no synchronization issue, so the surface flip is essentially the same as a nonstereo surface flip, with the exception that the physical surface being flipped contains two logical (left and right) surfaces.

In general, a passive display device reveals one half of the display's pixels to the left eye, and the other half to the right eye. This includes head-mounted displays and monitors featuring a grating overlaying the screen that filters alternate pixel columns to the left and right eye. Each eye is presented with images at the monitor's refresh rate.