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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