NEC uPD72257, Preliminary User'S Manual

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8.5 Rendering Pipeline
8.5.1 Coordinate transformation
Coordinate transformation as rotation, translation, projection and scaling must be
done on the application side. This is not part is the Drawing Engine hardware or
driver.
As all coordinates fed into the Drawing Engine are in fixed point format these
calculations can be done in fixed point format and don’t need a floating point unit.
8.5.2 Rasterization
During rasterization the vector data of the object has to be converted to pixel data.
This is done by setting up edge interpolation hardware (called limiter) for each
edge of the object that calculate a decision value, that is used to decide on which
side of the edge the pixel is positioned. There are six hardware limiters build into
the Ravin Drawing Engine.
In the linear setup a limiter describes a half plane. The intersection of all halfplanes
is the object. If three halfplanes are intersected a triangle is created.
Figure 8-4 Intersection of halfplanes
The limiter output is clamped to an interval of [0;1]. In limiter 1 and 2 it is possible
to apply a band filter before the clamping operation. Then the limiter is not
describing a half plane but a small band. With this setup a single limiter can
describe a thick line of infinite length.
The output of the different limiters can be combined by the combiner units with a
maximum or minimum operation. Maximum operation describes the union of both
halfplanes and minimum operation describes the intersection of both halfplanes.
Drawing Engine Chapter 8
Preliminary User's Manual S19203EE1V3UM00
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