def polygon_clip()

in threedod/benchmark_scripts/utils/box_utils.py [0:0]

• 30 lines of code
• 7 McCabe index (conditional complexity)

def polygon_clip(subjectPolygon, clipPolygon):
    """ Clip a polygon with another polygon.
    Ref: https://rosettacode.org/wiki/Sutherland-Hodgman_polygon_clipping#Python
    Args:
      subjectPolygon: a list of (x,y) 2d points, any polygon.
      clipPolygon: a list of (x,y) 2d points, has to be *convex*
    Note:
      **points have to be counter-clockwise ordered**
    Return:
      a list of (x,y) vertex point for the intersection polygon.
    """

    def inside(p):
        return (cp2[0] - cp1[0]) * (p[1] - cp1[1]) > (cp2[1] - cp1[1]) * (p[0] - cp1[0])

    def computeIntersection():
        dc = [cp1[0] - cp2[0], cp1[1] - cp2[1]]
        dp = [s[0] - e[0], s[1] - e[1]]
        n1 = cp1[0] * cp2[1] - cp1[1] * cp2[0]
        n2 = s[0] * e[1] - s[1] * e[0]
        n3 = 1.0 / (dc[0] * dp[1] - dc[1] * dp[0])
        return [(n1 * dp[0] - n2 * dc[0]) * n3, (n1 * dp[1] - n2 * dc[1]) * n3]

    outputList = subjectPolygon
    cp1 = clipPolygon[-1]

    for clipVertex in clipPolygon:
        cp2 = clipVertex
        inputList = outputList
        outputList = []
        s = inputList[-1]

        for subjectVertex in inputList:
            e = subjectVertex
            if inside(e):
                if not inside(s):
                    outputList.append(computeIntersection())
                outputList.append(e)
            elif inside(s):
                outputList.append(computeIntersection())
            s = e
        cp1 = cp2
        if len(outputList) == 0:
            return None
    return (outputList)