Intel 815 manual Source Data

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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Figure 13. Representation of On-Screen 6x4 Array of Pixels in the Frame Buffer

(0, 0)	(639, 0)
	63	32 31	0
			270F8h
			28100h
			28108h
256, 256	261, 256
			270F8h
			28100h
	256th Scan Line		28108h
	257th Scan Line
	258th Scan Line
	259th Scan Line		270F8h
			28100h
			28108h
256, 259	261, 259
			270F8h
			28100h
	Note: Drawing is not to scale		28108h
(0, 479)	(639, 479)
		b_blt6.vsd

Since there are other pixels on each of the scan lines on which this 6x4 block exists that are not part of this 6x4 block, what appears to be a single 6x4 block of pixels on the display must be represented by a discontinuous block of graphics data made up of 4 separate sub-blocks of six bytes apiece in the frame buffer at addresses 28100h, 28380h, 28600h, and 28880h. This situation makes the task of reading what appears to be a simple 6x4 block of pixels more complex. However, there are two characteristics of this 6x4 block of pixels that help simplify the task of specifying the locations of all 24 bytes of this discontinuous block of graphics data: all four of the sub-blocks are of the same length, and the four sub- blocks are separated from each other at equal intervals.

The BLT engine is designed to make use of these characteristics of graphics data to simplify the programming required to handle discontinuous blocks of graphics data. For such a situation, the BLT engine requires only four pieces of information: the starting address of the first sub-block, the length of a sub-block, the offset (in bytes), pitch, of the starting address of each subsequent sub-block, and the quantity of sub-blocks.

6.2.2.Source Data

The source data may exist in the frame buffer or main memory graphics memory where the BLT engine may read it directly, or it may be provided to the BLT engine by the host processor through the command packets. The block of source graphics data may be either contiguous or discontinuous, and may be either in color (with a color depth that matches that to which the BLT engine has been set) or monochrome.

The source select bit in the command packets specifies whether the source data exists in the frame buffer or is provided through the command packets. Monochrome source data is always specified as being supplied through an immediate command packet.

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