The architecture of QuickDraw had always allowed the creation of GrafPorts and their associated BitMaps or PixMaps "offscreen", where graphics could be composed in memory without it being visible immediately on the screen. Pixels could be transferred between these offscreen ports and the screen using the QuickDraw blitting function CopyBits. Such offscreen compositing is the workhorse for games and graphics-intensive applications. However, until the advent of 32-Bit QuickDraw, such offscreen worlds had to be created and set up by hand by the programmer within his application, and involving as it did three or more separate and fairly complex data structures (CGrafPort, PixMap and GDevice, and for indexed devices, the color look-up table and its inverse), could be error prone. With 32-Bit QuickDraw, OS support for handling this was added, with the "Offscreen Graphics World" or GWorld. The video buffer (PixMap) of a GWorld could be stored in main memory, or when available in unused parts of video ram where copying to the screen could be optimized for speed by avoiding the need to transfer a large amount of pixel data across the main memory bus.