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Graphics Programming
TVP4020
Programmers Reference Manual
96
The YUV conversion is done on data that is being loaded into the Texel0
register. The data for this may come from the TextureRead unit or from
the host, so YUV conversion can be done either during texture download
or on a texture as it is applied to a primitive. The YUV data can be in
either 444 format or 422 format. The chroma test may be done with
either YUV or RGB data.
5.9.1
Chroma Test
The chroma test specifies upper and lower bounds against which the
Texel0 value is tested. The test may be set to pass if the components of
Texel0 are either all inside or all outside the bounds. This is controlled
by the accept/reject TestMode options of the YUVMode register. If the
test passes, the Texel0 data may be used in the Texture/Fog/Blend unit
as normal. If the test fails, then the fragment to which the texture data
maps, may be rejected (not plotted). This is useful for cut-outs and
sprites. Alternatively, on test failure, the Texel0 value may be rejected
and the texture operation on the fragment suppressed. This is achieved
by setting the RejectTexel bit in the YUVMode register. In this case the
underlying color provided by P
ERMEDIA
is used without being modified by
the texture color. This is useful for applying a logo to a shaded polygon
where the underlying color is provided by the Color DDA unit.
The test modes available are:
Mode
Test Mode
0
No test
1
Accept
2
Reject
Table 5.17
Chroma Test Modes
Chroma key testing can be done without texture mapping by setting the
TexelDisableUpdate field in the YUVMode register. This allows fragment
rejection during a copy operation. If chroma testing is required against
the destination color of a copy (i.e. only overwrite pixels of the specified
color), then the destination region of the screen is used as the texture
map and the framebuffer units are set-up to do a normal copy. The
texels are read in and tested. Fragments are rejected if the colors do not
match. The copy operation for that pixel will not take place if the
fragment has been rejected. Setting the TexelDisableUpdate bit discards
the texel as soon as the test has been done which improves
performance.
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 ...