BOB (computer graphics)

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A BOB is a graphic object known from the Amiga computer, which can be moved on the screen like a sprite . The name BOB is derived from blitter object .

Bobs differ from sprites in that bobs are actually copied into the image memory, while hardware sprites are in their own registers or memory areas and are only switched into the data stream at the time of display. Unlike sprites, bobs are not limited in size or number. There is also the term software sprite , which is nothing more than a bob realized in software. Software sprites are also called shape .

A blitter is responsible for the extremely fast moving or copying of large memory areas within a certain address space , that is also within the area for image reproduction. To display a moving object, the area of ​​the background on which the object is to be displayed is first copied as a raster graphic in a buffer and saved there. Then a graphic of the object to be moved is copied from another buffer onto the background and thus displayed. To move the object, the saved partial background and the object to be displayed are copied alternately onto the background. With each copy the coordinates are adjusted according to the desired movement. Bobs therefore require considerably more computing power than sprites, since each copying process requires direct memory access to copy the graphic data to the screen memory . However, a blitter is able to carry out such processes extremely quickly and independently of the main processor .

A blitter unit is usually integrated directly into the memory management ICs , for example in the Agnus of the Amiga from Commodore or in the planned but never series-produced C65 , of which only a few prototypes exist.

literature

  • Commodore-Amiga Inc., Reading MA, The Amiga Hardware Reference Manual . ISBN 0-201-18157-6 .