Before
1 1
1
1 1
1
1 1 1
1 1
11
1 1
1 1 1
1
1 1
1
1
1
1 1
11
1 1
1
1
After
111
111111
11
111
1111111
11
1111
11111111
11
11111
111111111
11
111111111111111111
11111
111111111
11
1111
11111111
11
111
1111111
11
Figure
6-8:
Use
of the FCI Bit - Bit Is a 1
EXCLUSIVE
AREA
FIT..LING
There are two
fill
enable bits within BLTCONl. They are called IFE (for "Inclusive Fill
Enable") (used in the previous examples), and EFE (for "Exclusive Fill Enable") (used
in
the example below).
Exclusive
fill
enable means to exclude (remove) the outline on the trailing edge (left side)
of the
fill.
Since the blitter is running in descending mode during a
fill,
the trailing edge is formed
from the leftmost of each pair of bits on a horizontal line.
If
you wish to produce very sharp, single-point vertices, exclusive-fill enable must be
used. Figure
6-9
shows
how
a single-point vertex
is
produced using exclusive-fill enable.
182 Blitter Hardware
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