Before
After
Exclusive
Fill
1 1
1 1
1111
1111
1 1
1 1
111 111
1 1
1 1
11
11
11
11
1
1
1 1 1 1
11
11
1
1
1 1
111 111
1
1
1
1
1111 1111
Figure
6-9:
Single-Point Vertex Example
Line
Drawing
In.
addition to all the functions described above, the blitter has a line-drawing mode.
The
line-drawing mode is selected by placing a 1
in
bit 0 of BLTCON1, which causes
redefinition of some of the other control bits in BLTCONO and BLTCONl.
(See
the
description of the BLTCON registers
in
the appendix for the meanings of the other con-
trol bits.)
In
line-drawing mode, the blitter has the following features:
o Draws lines up
to
1,024 pixels long (twice as big as the high-resolution screen).
o Draws lines with regular or inverse video.
o Draws solid lines or textured lines.
o Draws special lines with one dot on each scan line, for use with area
fill.
Many of the blitter registers serve other purposes in line-drawing mode. These registers
and their functions are itemized
in
table
6-2
for reference purposes. Consult the appen-
dix for more detailed descriptions of the use of these registers and control bits
in
line-
drawing mode.'
Blitter Hardware
183
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