O

odd field

The first field comprising a video frame in an odd/even field set.

off-screen surface

A conceptually rectangular area in memory that is generally used to store bitmaps to be blitted to a back buffer before being displayed. Commonly used to store sprites.

opcode

Operation code that defines how to interpret the vertices in an execute buffer or how to change the state of the system.

overdraw

The average number of times to which a screen pixel is written.

overlay surface

A conceptually rectangular area in memory whose stored image information covers the image information of the primary surface to which it is applied. Overlays are assumed to be on top of all other screen components.

overlay z-order

Determines the order in which overlays clip each other, enabling a hardware sprite system to be implemented under DirectDraw.