point_in_poly.coffee

  pointInPoly = (point,poly) ->
    segments = for pointA, index in poly
                 pointB = poly[(index + 1) % poly.length]
                 [pointA,pointB]
    intesected = (segment for segment in segments when rayIntesectsSegment(point,segment))
    intesected.length % 2 != 0

  rayIntesectsSegment = (p,segment) ->
    [p1,p2] = segment
    [a,b] = if p1.y < p2.y
              [p1,p2]
            else
              [p2,p1]
    if p.y == b.y || p.y == a.y
      p.y += Number.MIN_VALUE

    if p.y > b.y || p.y < a.y
      false
    else if p.x > a.x && p.x > b.x
      false
    else if p.x < a.x && p.x < b.x
      true
    else
      mAB = (b.y - a.y) / (b.x - a.x)
      mAP = (p.y - a.y) / (p.x - a.x)
      mAP > mAB