![background image](http://html.mh-extra.com/html/texas-instruments/tvp4020-permedia-2/tvp4020-permedia-2_reference-manual_1097169069.webp)
Graphics Programming
TVP4020
Programmers Reference Manual
60
• LimitsEnable. When enabled, this allows quick rejection of fragments outside the
defined area.
• BitMaskRelative. If enabled, this specifies that the bitmask should be accessed by an
index made up of the lower 5 bits of the X coordinate of the current fragment.
5.3.12
Synchronization
For most circumstances
P
ERMEDIA
will automatically synchronize
between primitives so that data for the first primitive is written before
data for the second primitive is read. This is handled by data type, so
localbuffer reads and writes are synchronized as are framebuffer reads
and writes, but localbuffer reads are not synchronized with framebuffer
writes.
If a unit is used to modify data that is not its normal type, then it may be
necessary to explicitly synchronize the pipeline. If the Framebuffer Write
unit is used to clear the localbuffer with block fills then the pipeline must
be synchronized before localbuffer data is read. If the Framebuffer Write
unit is used to download a texture map, the pipeline must be
synchronized before the Texture Read unit accesses the texture.
Explicit synchronization of the pipeline is done by the WaitForCompletion
command. This has no data field, and may be inserted into a stream of
commands; there is no need to wait for P
ERMEDIA
to report that
synchronization has taken place.
Alternatively, synchronization must be done with the Sync command, but
this does require the host processor to poll the chip until it reports that
the pipeline is idle (see the section on the Host Out unit).
5.3.13
X and Y limits clipping
The Rasterizer will normally rasterize all pixels on every scanline,
generating a fragment per pixel. If large numbers of scanlines are
subsequently clipped out by, for example, the scissor unit, then a lot of
time can be wasted. The Ylimits register has been added to provide a
way of quickly eliminating whole scanlines for a given primitive. This
register effectively provides a Y scissor clip in the Rasterizer.
If limits testing has been enabled in the RasterizerMode register, and if a
scanline being rasterized falls outside the Y limits bounds, then the
Rasterizer will move directly onto the next scanline without rasterizing in
X.
The Xlimits register has been added to avoid unnecessary rasterization,
but does not act as a true X scissor clip. This is to ensure correct
interpolation of color, fog etc. The limits registers are provided for
efficiency reasons.
Both X and Y Limits clipping are automatically disabled when
SyncOnHostData or SyncOnBitMask is used.
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 ...