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Motorola DSP96002 User Manual

Page 602

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MOTOROLA

DSP96002 USER’S MANUAL

B-83

If the point is found to lie outside the viewing pyramid, an algorithm to clip a single point is performed and

the program enters the trivial reject loop.

The trivial reject loop assumes that the last displayed point was outside the viewing pyramid. It pulls a new

point from the input list, converts it to clipping space and checks if the line joining the new point and the

last point can be trivially rejected. Trivial rejection occurs when both points of a line lie outside of a clipping

plane. When this occurs, the current point is saved and the trivial reject loop repeats.

Should the line not be trivially rejected but the current point is accepted, an algorithm to clip a single point

is performed. If the current point is not accepted, two-point clipping is performed.

PERFORMANCE

All times are given in instruction cycles.

Accept loop

First point 38

Each additional point 39

Accept single point clip

Minimum (single plane) 68

Maximum (three planes) 94

Reject loop

Each point 37

Reject single point clip

Minimum (single plane) 89

Maximum (three planes) 115

Reject double clip line drawn

Minimum (two single planes) 145

Maximum (six planes) 206

Reject double clip line rejected

Minimum (two single planes) 112

Maximum (six planes) 173

The DSP96002 has an instruction cycle time of 74ns and will transform 347K points/sec in the accept loop.

In the reject loop, 365K points can be rejected each second.

INPUT

Before calling the polyline generator, address register r1 should point to the area in X memory which con-

tains the X, Y and Z coordinates of the input points. Data register d7.l should contain the number of points

in the polyline in the form of a 32-bit integer.