NEC uPD72257, Preliminary User'S Manual

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The final output is then used as an alpha value. Edge antialiasing can be done
with no additional effort with this hardware.
To calculate the decision value for the each possible pixel with a limiter the
bounding box of the object has to be calculated. After that the decision value for
the top left corner of the bounding box has to be calculated for each edge. Then
the increments for a step in x and a step in y direction have to be calculated. This
is done by the CPU in the driver.
With this information the Drawing Engine scans the whole bounding box and
calculates the decision value for every pixel incrementally. A block diagram of the
whole rasterization unit can be seen in figure "Simplified rendering pipeline setup"
in the chapter "Introduction".
clamp
Limiter1 Limiter2 Limiter3 Limiter4 Limiter5 Limiter6
Bandfilter
clamp clamp clamp clamp clamp
Combiner A Combiner B Combiner D
Combiner C
Combiner out
alpha output
Bandfilter
Figure 8-5 Block diagram of the rasterization unit
Chapter 8 Drawing Engine
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Preliminary User's Manual S19203EE1V3UM00