Draw_VL_ab ($F3D8)

This routine draws vectors between the set of (y,x) points pointed to by the X register. The vector list has the following format:

rel y, rel x, rel y, rel x, ...

ENTRY:

DP = $D0

A-reg = the number of vectors to draw

B-reg = the scale factor

X-reg points to the vector list

EXIT:

X-reg points to next byte after list

D-reg trashed