The blitter is one of the two coprocessors in the Amiga. Part of the Agnus chip, it is used to copy rectangular blocks of memory around and to draw lines. When copying memory, it is approximately twice as fast as the 68000, able to move almost four megabytes per second. It can draw lines at almost a million pixels per second. In block move mode, the blitter can perform any logical operation on up to three source areas, it can shift up to two of the source areas by one to fifteen bits, it can fill outlined shapes, and it can mask the first and last words of each raster row. In line mode , any pattern can be imposed on a line, or the line can be drawn such that only one pixel per horizontal line is set. The blitter can only access Chip memory -- that portion of memory accessible by the display hardware. Attempting to use the blitter to read or write Fast or other non-Chip memory may result in destruction of the contents of Chip memory. A "blit" is a single operation of the blitter -- perhaps the drawing of a line or movement of a block of memory. A blit is performed by initializing the blitter registers with appropriate values and then starting the blitter by writing the BLTSIZE register. As the blitter is an asynchronous coprocessor, the 680x0 CPU continues to run as the blit is executing.
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