图形裁剪(Cohen-Surtherland算法)

from matplotlib import pyplot as plt

"""
函数说明：判断点超出哪个边界
"""
def edgeCode(x,y,yEdge,xEdge):
    code = 0
    if x < xEdge[0]:
        code = code|1
    if x > xEdge[1]:
        code = code|2
    if y < yEdge[0]:
        code = code|4
    if y > yEdge[1]:
        code = code|8
    return code

"""
函数说明：cohenSurtherland 
parameter: pointX:点X的集合
           pointY:点Y的集合
           yEdge:上下边界
           xEdge:左右边界
           pic：图
"""
def cohenSurtherland(xEdge,yEdge,pointX,pointY,pic):
    #边界区域
    mid   = 0
    leftEdge = 1
    rightEdege = 2
    bottomEdge = 4
    topEdge = 8

    pointX.append(pointX[0])
    pointY.append(pointY[0])

    for i in range(len(pointX)-1):

        time = 0  #用于判断线段完全处于外部的情况

        x0 = pointX[i]
        y0 = pointY[i]
        x1 = pointX[i+1]
        y1 = pointY[i+1]

        code0 = edgeCode(x0,y0,xEdge,yEdge)
        code1 = edgeCode(x1,y1,xEdge,yEdge)
        while True:
            if not(code0|code1) :  #线段部分全部位于内部
                pic.plot([x0,x1],[y0,y1],c = 'r')
                break;
            elif (code0&code1 or time > 3) :  #线段全部位于外部
                break;
            else :
                if(x1!=x0):
                    k = (y1 - y0) / (x1 - x0)
                    dk = 1/k #k的倒数
                else:
                    dk = 0
                #判断哪个端点位于外部
                if code0 :
                    codeout = code0
                    temp = 0
                else:
                    codeout = code1
                    temp = 1
                #判断出界的方向并且更新点
                if  codeout&leftEdge :
                    y = pointY[i+temp]+k*(xEdge[0]-pointX[i+temp])
                    x = xEdge[0]
                elif codeout&rightEdege :
                    y = pointY[i+temp]+k*(xEdge[1]-pointX[i+temp])
                    x = xEdge[1]
                if codeout&topEdge :
                    x = pointX[i+temp]+dk*(yEdge[1]-pointY[i+temp])
                    y = yEdge[1]
                elif codeout&bottomEdge:
                    x = pointX[i+temp]+dk*(yEdge[0]-pointY[i+temp])
                    y = yEdge[0]
                if temp :
                    x1 = x
                    y1= y
                    code1 = edgeCode(x1,y1,xEdge,yEdge)
                else    :
                    x0 = x
                    y0 = y
                    code0 = edgeCode(x0,y0,xEdge,yEdge)
                time+=1



def tes(ax2):
    a = 8
    b = 0
    print(a|b)
if __name__ == '__main__':
    #左右 下上边界
    xEdge = [10,30]
    yEdge = [10,30]
    #点集
    pointX = [20,20,40,35,25,32,27,20]
    pointY = [25,45,40,15,20,30,35,25]

    pic0 = plt.subplot(1,2,1)
    pic0.axis([0,50,0,50])
    pic0.plot([10,30,30,10,10],[10,10,30,30,10])
    pic0.plot(pointX,pointY,c = 'r')

    pic1 = plt.subplot(1,2,2)
    pic1.axis([0, 50, 0, 50])
    pic1.plot([10,30,30,10,10],[10,10,30,30,10])

    cohenSurtherland(xEdge,yEdge,pointX,pointY,pic1)

    plt.show()