Blitter object

A bob is a graphic object which can be moved similar to a sprite on the screen. The name derives from Bob blitter object.

Bobs differ from sprites in that Bobs are actually copied into the frame buffer, while hardware sprites are in separate registers or memory locations and are only connected to the display time in the data stream. Unlike sprites Bobs are not limited in size and number. There is also the term software - sprite, which, however, as one is no longer implemented in software Bob. Software Sprites are also called shape.

A blitter is responsible for the extremely fast moving or copying large storage areas within a particular address space, that is well within the range for image reproduction. In order to represent a moving object, first, the range of the background on which the object is to be displayed, copied as a raster image into a buffer, and secured there. Then a graphic of the moving object to be copied from another buffer on the background and thus represented. To move the object, alternately secured part - background and the object being rendered are always copied to the background. Each Copy the coordinates corresponding to the desired movement to be adjusted. Therefore Bobs require substantially more computing power than sprites, since each copy operation requires a direct memory access to copy the graphics data in the display memory. However, a blitter is able to perform such operations very quickly and independently from the main processor.

A blitter unit is typically integrated directly into the IC memory management, such as the Agnus of the Amiga from Commodore or the planned but never built in series C65, of which only a few prototypes exist.