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o
MASKING - The blitter can mask the leftmost and rightmost data word from
each horizontal line. Mask registers are provided for the first and the last words
on every line of blitter data. This allows logic operations on bit-boundaries from
both the left and the right edge of a rectangular region.
o
ZERO DETECTION - The blitter can
~tore
the result of the logic operations
back into memory or simply sense whether there were any 1 bits present as a
result of the logic operation. This feature can be used for hardware-assisted
software collision detection.
o
AREA-FILLING - The blitter can perform a hardware-assisted area fill between
pre-drawn lines.
o
LINE-DRAWING - The blitter can draw ordinary lines at any angle and can
also apply a pattern to the lines it draws. It can also draw special lines with one
pixel dot per horiiontalline (a special mode needed for use with the blitter fill
operation ).
Data Copying
The primary purpose of the blitter is to copy (transfer) data in large blocks from one
memory location to another, with or without processing. The name "blitter" stands for
"block image transferrer."
Images in memory are usually stored in a linear fashion; each word of data on a line is
located at an address that is one greater than the word on its left. (See figure 6-1).
Note that each line is a "plus one" continuation of the previous line.
Blitter Hardware 167
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