Graphics Programming
TVP4020
Programmers Reference Manual
90
If the texture is in Color Index mode (either 4 or 8 bits) the single value is
repeated for all color components. If the framebuffer format is also Color
Index, the single value is used as the pixel color; if the framebuffer is
RGBA, then the texture value becomes grey scale.
The texture values may be indexed through a 256 entry look-up table.
Each entry of the table holds a 32 bit RGBA value. If the CI8 texture is
used, then the whole LUT is used for each texture; if the CI4 texture
format is used each texture uses 16 entries, so 16 separate LUTs may
be loaded and the appropriate one indexed (the upper 4 bits of the index
are supplied by the upper 4 bits of TexelLUTIndex).
If an RGB or RGBA texture format is used (as opposed to CI8 or CI4)
the individual R, G, B, and A components are indexed separately which
allows remapping functions such as gamma correction.
5.8.5
Registers
The TextureReadMode register controls the way that textures are read
from memory.
The S and T wrap modes can be set to clamp, repeat or mirror as
described earlier.
With Filter Mode disabled, nearest-neighbor texture mapping will be
performed. With this bit set, bilinear filtering is enabled.
The Packed Data bit is used to define how texels are read from memory.
If this bit is cleared, each texel is read one at a time; if set several texels
can be read simultaneously improving efficiency. The actual number of
texels read in this case is dependent on the texel size. See section
§5.10.4 for how this can be used for packed copies.
The TextureReadMode register controls the way that textures are read
from memory. With Filter Mode disabled, nearest-neighbor texture
mapping will be performed. With it set, bilinear filtering is enabled.
0
8
16
24
31
Reserved
TWrapMode
Enable
Reserved
Reserved
Height
Width
Packed Data
Filter Mode
SWrapMode
Figure 5.25
TextureReadMode Register
Содержание TVP4020 PERMEDIA 2
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