Intel 815 manual Destination Source Bblt4.vsd

Models: 815

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Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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The figure below illustrates how this feature of the BLT engine can be used to perform the same BLT operation as was illustrated in the figure above, while avoiding the corruption of source data. As shown in the figure below, the BLT engine reads the source data and writes the data to the destination starting with the right-most pixel of the bottom-most line. By doing this, no pixel existing where the source and destination locations overlap will ever be written to before it is read from by the BLT engine. By the time the BLT operation has reached step (e) where two pixels existing where the source and destination locations overlap are about to be over written, the source data for those two pixels has already been read.

Figure 11. Suggested Starting Points for Possible Source & Destination Overlap Situations

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b_blt4.vsd

The figure above shows the recommended lines and pixels to be used as starting points in each of 8 possible ways in which the source and destination locations may overlap. In general, the starting point should be within the area in which the source and destination overlap.

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Page 56
Image 56
Intel 815 manual Destination Source Bblt4.vsd