Graphics Programming
TVP4020
Programmers Reference Manual
66
Several long-term Rasterizer modes are stored in the RasterizerMode
register as shown below:
Bit
No
Name
Description
0
MirrorBitMask
When this bit is set the bitmask bits are consumed from the most
significant end towards the least significant end.
When this bit is reset the bitmask bits are consumed from the least
significant end towards the most significant end.
1
InvertBitMask
When this bit is set the bitmask is inverted first before being
tested.
2,3
FractionAdjust
These bits are for the ContinueNewLine command and specify
how the fraction bits in the Y and XDom DDAs are adjusted:
0: No adjustment is done
1: Set the fraction bits to zero
2: Set the fraction bits to half
3: Set the fraction to
nearly half
, i.e. 0x7fff
4,5
BiasCoordinates
These bits control how much is added onto the StartXDom,
StartXSub and StartY values when they are loaded into the DDA
units. The original registers are not affected:
0: Zero is added
1: Half is added
2:
Nearly half
, i.e. 0x7fff is added
6
ForceBackgroundColo
r
This bit, when set, causes the color to be taken from the Texel0
register instead of the normal color if the bitmask test fails.
7,8
BitMaskByteSwapMod
e
Controls byte swapping of the bitmask. If input is ABCD,
0: ABCD
1: BADC
2: CDAB
3: DCBA
9
BitMaskPacking
If enabled, the current bitmask is discarded at the end of every
scanline even if it has not been finished.
0: Enabled
1: Disabled
10..1
4
BitMaskOffset
Position of first bit to test in bitmask.
15,16
HostdataByteSwapMo
de
Controls byte swapping of host data. If input is ABCD,
0: ABCD
1: BADC
2: CDAB
3: DCBA
17
Reserved
18
LimitsEnable
If enabled, quickly reject areas of primitive outside defined area.
0: Disabled
1: Enabled
19
BitMaskRelative
Controls whether bitmask is indexed by counter or by lower 5 bits
of X value.
0: Disabled
1: Enabled
Table 5.7
Rasterizer Mode Register
Содержание TVP4020 PERMEDIA 2
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