Question

Given a series of points, how could I calculate the vector for that line 5 pixels away? Ex:
Given:

   \
    \
     \

How could I find the vector for

   \  \
    \  \
     \  \

The ones on the right.

I’m trying to figure out how programs like Flash can make thick outlines.

Thanks

Answer 1

A thick line is a polygon. (Let’s forget about antialiasing for now)

picture http://img39.imageshack.us/img39/863/linezi.png

start = line start = vector(x1, y1)
end = line end = vector(x2, y2)
dir = line direction = end – start = vector(x2-x1, y2-y1)
ndir = normalized direction = dir*1.0/length(dir)
perp = perpendicular to direction = vector(dir.x, -dir.y)
nperp = normalized perpendicular = perp*1.0/length(perp)

perpoffset = nperp*w*0.5
diroffset = ndir*w*0.5

(You can easily remove one normalization and calculate one of the offsets by taking perpendicular from the other)

p0, p1, p2, p3 = polygon points:
p0 = start + perpoffset – diroffset
p1 = start – perpoffset – diroffset
p2 = end + perpoffset + diroffset
p3 = end – perpoffset + diroffset

P.S. You’re the last person I ever going to explain this stuff to.
Things like these should be understood on intuitive level.