Intel 815 manual 185

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.

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