python实现cohen-sutherland裁剪

Cohen-Sutherland裁剪算法是一种基于二维直线段裁剪的算法，下面是Python实现的代码：

# 定义区域码
INSIDE = 0  # 0000
LEFT = 1    # 0001
RIGHT = 2   # 0010
BOTTOM = 4  # 0100
TOP = 8     # 1000

# 计算区域码
def computeCode(x, y, xmin, ymin, xmax, ymax):
    code = INSIDE
    if x < xmin:           # left of rectangle
        code |= LEFT
    elif x > xmax:         # right of rectangle
        code |= RIGHT
    if y < ymin:           # below rectangle
        code |= BOTTOM
    elif y > ymax:         # above rectangle
        code |= TOP
    return code

# Cohen-Sutherland裁剪算法
def cohenSutherlandClip(x1, y1, x2, y2, xmin, ymin, xmax, ymax):
    # 计算起点和终点的区域码
    code1 = computeCode(x1, y1, xmin, ymin, xmax, ymax)
    code2 = computeCode(x2, y2, xmin, ymin, xmax, ymax)
    accept = False
    while True:
        if code1 == 0 and code2 == 0:  # 完全在裁剪区域内
            accept = True
            break
        elif code1 & code2 != 0:      # 完全在裁剪区域外
            break
        else:
            x, y = 0, 0
            codeOut = code1 if code1 != 0 else code2
            if codeOut & TOP:          # 线段与裁剪区域的上边界相交
                x = x1 + (x2 - x1) * (ymax - y1) / (y2 - y1)
                y = ymax
            elif codeOut & BOTTOM:     # 线段与裁剪区域的下边界相交
                x = x1 + (x2 - x1) * (ymin - y1) / (y2 - y1)
                y = ymin
            elif codeOut & RIGHT:      # 线段与裁剪区域的右边界相交
                y = y1 + (y2 - y1) * (xmax - x1) / (x2 - x1)
                x = xmax
            elif codeOut & LEFT:       # 线段与裁剪区域的左边界相交
                y = y1 + (y2 - y1) * (xmin - x1) / (x2 - x1)
                x = xmin
            if codeOut == code1:       # 更新起点
                x1, y1 = x, y
                code1 = computeCode(x1, y1, xmin, ymin, xmax, ymax)
            else:                      # 更新终点
                x2, y2 = x, y
                code2 = computeCode(x2, y2, xmin, ymin, xmax, ymax)
    if accept:
        return x1, y1, x2, y2
    else:
        return None

以上代码中，`computeCode`函数用于计算点的区域码，`cohenSutherlandClip`函数用于执行裁剪操作。其中，`(x1, y1)`和`(x2, y2)`是线段的起点和终点，`(xmin, ymin)`和`(xmax, ymax)`是裁剪区域的左下角和右上角坐标。函数返回裁剪后的线段端点坐标，如果裁剪区域和线段不相交，返回`None`。