Bit blit

[1] The Commodore Amiga's graphics chipset (and others) could combine three source bitmaps using any of the 256 possible 3-input boolean functions.

This is because bitwise operations on color displays do not usually produce results that resemble the physical combination of lights or inks.

Dan Ingalls, Larry Tesler, Bob Sproull, and Diana Merry programmed this operation at Xerox PARC in November 1975 for the Smalltalk-72 system.

Machines that rely heavily on the performance of 2D graphics (such as video game consoles) often have special-purpose circuitry called a blitter.

Because any value ORed with 0 is unchanged, the background is unaffected and the black areas are filled with the actual sprite image.

Blitting is similar to hardware-sprite drawing, in that both systems reproduce a pattern, typically a square area, at different locations on the screen.

This means that every time a foreground pattern is placed on the screen, any background pixels underneath it are overwritten, or "damaged".

It is up to the software to repair this damage by blitting twice, once to restore the pixels that were changed, and then again to place the foreground pattern in its new location.