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TVP4020
Programmers Reference Manual
Graphics Programming
45
16
SubPixelCorrectionEnab
le
When set (and qualified by the
SubPixelCorrectionEnable bit in the DeltaMode register)
enables the sub pixel correction of any value interpolated
in the Y direction. The rendering devices will perform the
sub pixel corrections in the X direction.
20
RejectNegativeFace
Qualified by the BackFaceCull field in the DeltaMode
register. If set rejects triangles with a negative area. If
clear, rejects triangles with a positive area.
Table 5.2
Draw Command Bit Field Assignments Affecting Delta
5.2.2
DrawLine Commands
The command DrawLine01 causes Delta to draw a line from vertex 0 -
V0 to vertex 1 - V1. Conversely DrawLine10 causes Delta to draw a line
from V1 to V0. These two commands allow polylines to be drawn by
updating V0 and V1 alternately. The alternate use of DrawLine01 and
DrawLine10 allows the line stipple pattern to continue correctly across
segments in a polyline.
Note, that due to the DDA algorithm, drawing direction may affect the
rendered pixels. Hence, with the same data in V0 and V1, the two
DrawLine commands may render different pixels. This may be important
for operations such as XOR lines or patterned lines.
5.2.3
Repeat Commands
The RepeatTriangle and RepeatLine commands allow the previously
set-up triangle or line to be repeated again. This is useful when some
rendering state has changed and the primitive must be redrawn. An
example of this is when the scissor region is updated and the primitive
redrawn to implement window clipping.
A RepeatTriangle command should only follow a DrawTriangle
command and not a DrawLine command. Mixing the incorrect Repeat
and Draw commands will cause undefined visual effects.
5.2.4
DeltaMode Register
The DeltaMode register is used to hold 'long term' state information. The
per primitive control information is taken from the Draw command as
already outlined. The following table lists the DeltaMode register bit field
assignments and describes their function.
Bit
No.
Name
Description
0, 1
Reserved
2, 3
DepthFormat
The following options apply:
0
15 bit depth
1
16 bit depth
2
Reserved
3
Reserved
Summary of Contents for TVP4020 PERMEDIA 2
Page 1: ...Texas Instruments TVP4020 PERMEDIA 2 Programmer s Reference Manual Issue 4 ...
Page 284: ...TVP4020 Programmers Reference Manual A Gouraud Shaded Triangle 275 ...
Page 292: ...TVP4020 Programmers Reference Manual Register Tables 283 ...
Page 314: ...TVP4020 Programmers Reference Manual Index 305 ...
Page 315: ...Index TVP4020 Programmers Reference Manual 306 Index ...
Page 323: ...Index TVP4020 Programmers Reference Manual 314 ...