TVP4020
Programmers Reference Manual
Graphics Programming
59
addition it is strongly recommended that any units which can discard
fragments (for instance the following tests: bitmask, user scissor, screen
scissor, stipple, depth, stencil), are disabled otherwise a shortfall in
pixels returned may occur, also leading to deadlock.
Note that because the area of interest in copy/upload/download
operations is defined by the Rasterizer, it is not limited to rectangular
regions.
Color formatting can be used when performing image copies, uploads
and downloads. This allows data to be formatted from, or to, any of the
supported P
ERMEDIA
color formats, section §5.12.6 fully describes this
operation.
5.3.11
Rasterizer Mode
A number of long-term modes can be set using the RasterizerMode
register, these are:
• Mirror BitMask: This is a single bit flag which specifies the direction that bits are
checked in the BitMaskPattern register. If the bit is reset, the direction is from least
significant to most significant (bit 0 to bit 31), if the bit is set, it is from most significant
to least significant (from bit 31 to bit 0).
• Invert BitMask: This is a single bit which controls the sense of the accept/reject test
when using a Bitmask. If the bit is reset then when the BitMask bit is set the fragment
is accepted and when it is reset the fragment is rejected. When the bit is set the
sense of the test is reversed.
• Fraction Adjust: These 2 bits control the action taken by the Rasterizer on receiving a
ContinueNewLine command. As P
ERMEDIA
uses a DDA algorithm to render lines, an
error accumulates in the DDA value. P
ERMEDIA
provides for greater control of the
error by doing one of the following:
•
leaving the DDA running, which means errors will be propagated along
a line.
•
or setting the fraction bits to either zero, a half or almost a half
(0x7FFF).
• Bias Coordinates: Only the integer portion of the values in the DDAs are used to
generate fragment addresses. Often the actual action required is a rounding of
values. This can be achieved by setting the bias coordinate bit to true which will
automatically add almost a half (0x7FFF) to all input coordinates.
• ForceBackgroundColor: When set, if a fragment fails the bitmask test it is not
discarded, but it is made to use the contents of the Texel0 register in place of the
normal color. This is used to provide foreground/background color selection.
• BitMaskByteSwapMode. This controls how or whether the bitmask is byte swapped a it
is loaded. Four different byte orders are supported.
• BitMaskPacking. Controls whether a bitmask is discarded at the end of a scanline or
continued onto the next. Not supported for block writes.
• BitMaskOffset. Sets the position of the first bit in the bitmask to test. Not supported for
block writes.
• HostDataByteSwapMode. Controls byte swapping of host data being sent to the chip.
This applies to any operation using the SyncOnHostData in the Render register. Four
different byte orders are supported.
Содержание TVP4020 PERMEDIA 2
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