User's Manual

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