[julia-users] Re: Clipping Algorithm

[Andreas Lobinger]

function inpoly(px,py,edges)
i = 0
for k=1:size(edges)[1]
 p1x = edges[k,1]
 p1y = edges[k,2]
 p2x = edges[k,3]
 p2y = edges[k,4]
 
 if (p1y < py) & (p2y < py) 
  continue
 end

 if (p1y >= py) & (p2y >= py) 
  continue
 end

 d = p2y - p1y
 s = (py-p1y)*(p2x-p1x)
 
 if d != 0
  sx = (s / d)+p1x
  if sx >= px
   i = i +1
  end
 end
end

return mod(i,2)
end

tests a single point (px,py) against a closed polygon in edges = [x1 y1 x2 
y2; x2 y2 x3 y3; x3 y3 x1 y1], the first point repeated as last point.