Motorola DSP96002 - Manual (Page 602)

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.