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TVP4010 and TVP4020 Differences
TVP4020
Programmers Reference Manual
298
F5.5
Block Fills
The block fill color register has been extended to 64 bits to allow greater
flexibility. Two new registers have been added, BlockColorUpper and
BlockColorLower, which set the upper and lower 32 bits of the color
respectively. If the TVP4010 BlockColor register is used, its contents are
used for both upper and lower halves of the block color giving full
backward compatibility.
Texture mapping has been extended to hold block fill masks. Designed
specifically for font caching, a byte packed font may be stored in local
memory and used to control which pixels are drawn by a block fill.
Any block fill pattern may be stippled using the normal stipple pattern
table.
The texture LUT can hold data that is used to update the block fill color
on each scanline. This is designed for pattern filling.
F5.6
Sprite Control
The chroma key testing has been extended to improve the quality of cut-
outs which have been bilinear filtered, and to smooth the edges of
sprites. Two additional registers, AlphaMapUpperBound and
AlphaMapLowerBound, have been added to define the range of colors
that should have their alpha value mapped to zero. The TVP4010
chroma key registers are used to reject the pixels with an alpha value
not equal to one. Texels that have failed the alpha map test are not
included in filtering, so edge effects often seen with filtered cut-outs are
removed.
The alpha values of the edge pixels are filtered so that they form a range
from one within the area to be drawn to zero within the area not to be
drawn. In the region close to the edge of what is to be drawn, the alpha
values are filtered to lie between zero and one. The range of alpha
values rejected by the chroma key test can be adjusted to allow fine
control over the exact size of the cut-out. If blending is enabled then the
varying alpha values smooth the transition of the edge of the sprite to
the background.
F5.7
Alpha Blending
An optimization has been added to TVP4020 which reduces the memory
bandwidth if blending is enabled. If the alpha value used for blending is
derived exclusively from a texture map, the FBReadMode register can
be set to disable reading of the framebuffer for any pixels for which the
corresponding texel has an alpha value of one. If the alpha value is one,
the final color will not include any of the previous framebuffer color so it
does not need to be read.
Содержание TVP4020 PERMEDIA 2
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Страница 292: ...TVP4020 Programmers Reference Manual Register Tables 283 ...
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