Blitter

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The Atari ST Bit-Block Transfer Processor (BLiTTER), in high level terms, is a chip dedicated to moving data around in memory independant of the main CPU, typically used to perform graphical operations smoothly (such as scrolling) while leaving the CPU to perform other tasks.

In low level terms, it is a hardware implementation of the bit-block transfer (BitBlt) algorithm. BitBlt can be simply described as a procedure that moves bit-aligned data from a source location to a destination location through a given logic operation.

Applications

The BitBlt primitive that is implemented in the blitter can be used to perform such operations as:

  • Area seed filling
  • Rotation by recursive subdivision
  • Slice and smear magnification
  • Brush line drawing using Bresenham DDA
  • Text transformations (eg. bold, italic, outline)
  • Text scrolling
  • Window updating
  • Pattern filling


Employment

Blitters of some sort were used in a number of Atari machines, and their competitors.

TOS Family

In the TOS Family, the blitter chip first became available in the Mega ST range, followed by the STE,Mega STE, the Falcon. It was also available as an upgrade for the standard ST range but not the TT.

Jaguar

The Jaguar contained a blitter

Lynx

The Lynx contained a blitter

Other

All models of the Amiga contained a blitter

Programming