NEC µPD72257 Preliminary User's Manual page 229

Drawing Engine
8.5.3.2
Note
Figure 8-9
Limiter operation
The Drawing Engine contains six limiters. Each limiter contains four registers:
• DRWLnSTART
• DRWLnXADD
• DRWLnYADD
The value register is not visible to the user and is just an internal register which is
then output. It is possible to drive the limiters in a threshold mode. Then all values
above 0 are considered 1. This is used in case antialiasing is not desired (e.g. for
shared edges).
In the diagram below following abbreviations are used:
• start = DRWLnSTART
• xadd = DRWLnXADD
• yadd = DRWLnYADD
Value=value+xadd
Flowchart of linear limiter operation
Preliminary User's Manual S19203EE1V3UM00
Begin
x=0
y=0
xadd=a
yadd=b
start=c
value=start
output value
x=x+1
yes
x<width
no
y=y+1
y<height
End
Chapter 8
start=start+yadd
yes
229