User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0
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Bit Descriptions
13 Text BLT. Current Opcode is Text BLT.
12 Scan Line BLT. Current Opcode is Scan Line BLT.
11 Pixel BLT. Current Opcode is Pixel BLT.
10:8 Destination Transparency Mode. These bits control whether or not the byte(s) at the destination
corresponding to a given pixel will be conditionally written, and what those conditions are. This
feature can make it possible to perform various masking functions in order to selectively write or
preserve graphics data already at the destination.
All four of the sets of conditions that may be chosen as the controlling factor in performing color
transparency involve comparing the color that has been specified to be used in the color expansion
of any monochrome source data to other colors. This background color is in the Source Expansion
Background Color Register.
XX0 = No color transparency mode enabled. This causes normal operation with regard to writing
data to the destination.
001 = The color specified as the background color for use in the color expansion of monochrome
source data is compared to the color resulting from the bit-wise operation performed for each
pixel. If these two colors are not equal, then the byte(s) at the destination corresponding to the
current pixel are written with the result of the bit-wise operation. [Source color transparency].
011 = The color specified as the background color for use in the color expansion of monochrome
source data is compared to the color specified by the byte(s) at the destination corresponding
to the current pixel. If these two colors are not equal, then the byte(s) at the destination
corresponding to the current pixel are written with the result of the bit-wise operation.
101 = The color specified as the background color for use in the color expansion of monochrome
source data is compared to the color resulting from the bit-wise operation performed for each
pixel. If these two colors are equal, then the byte(s) at the destination corresponding to the
current pixel are written with the result of the bit-wise operation.
111 = The color specified as the background color for use in the color expansion of monochrome
source data is compared to the color specified by the byte(s) at the destination corresponding
to the current pixel. If these two colors are equal, then the byte(s) at the destination
corresponding to the current pixel are written with the result of the bit-wise operation.
[Destination color transparency]
7:5 Pattern Vertical Alignment. Specifies which scan line’s worth (which 1 of the 8 horizontal rows) of
the 8x8 pattern will appear on the first scan line’s worth of the data written to the destination.
Depending upon the location of the destination, the upper left-hand corner of the upper left-hand tile
of the pattern is usually aligned with the upper left-hand corner of the block of data written to the
destination. The BLT Engine determines the horizontal alignment relative to the destination from the
lower bits of the destination address, however, the vertical alignment relative to the destination must
be supplied through these bits.
4 Destination Read Modify Write. This bit is decoded from the last instruction’s opcode field and
Destination Transparency Mode to identify whether a Destination read is needed.
3 Color Source. This bit is decoded from the last instructions opcode field to identify whether a color
(1) source is used.
2 Monochrome Source. This bit is decoded from the last instructions opcode field to identify whether
a monochrome (1) source is used.
1 Color Pattern. This bit is decoded from the last instructions opcode field to identify whether a color
(1) pattern is used.
0 Monochrome Pattern. This bit is decoded from the last instructions opcode field to identify whether
a monochrome (1) pattern is used.