C 代码实现：两条线段的交点计算

double XX[4], YY[4];
double ALX1, ALX2, ALY1, ALY2, EPS;
double NTT1, NTT2, NTT3, NTT4;
double AK12, B12, XX11, YY11, VALUE1, VALUE2, VALUE3, BBX, BBY;
double AK, BB, XX12, YY12, XX13, YY13, T;

XX[0] = XN(NTT1);
XX[1] = XN(NTT2);
XX[2] = XN(NTT3);
XX[3] = XN(NTT4);
YY[0] = YN(NTT1);
YY[1] = YN(NTT2);
YY[2] = YN(NTT3);
YY[3] = YN(NTT4);

if (fabs(ALX2-ALX1) >= EPS || fabs(XX[1]-XX[0]) >= EPS) {
    if (fabs(ALX2-ALX1) < EPS && fabs(XX[1]-XX[0]) >= EPS) {
        AK12 = (YY[1]-YY[0])/(XX[1]-XX[0]);
        B12 = YY[0] - AK12*XX[0];
        XX11 = ALX1;
        YY11 = AK12*XX11 + B12;
        VALUE1 = (YY11-YY[1])*(YY11-YY[0]);
        VALUE2 = (YY11-ALY1)*(YY11-ALY2);
        VALUE3 = (XX11-XX[1])*(XX11-XX[0]);
        if (VALUE1 <= 0 && VALUE2 <= 0 && VALUE3 <= 0) {
            BBX = XX11;
            BBY = YY11;
        }
    }
    if (fabs(XX[1]-XX[0]) < EPS && fabs(ALX2-ALX1) >= EPS) {
        AK = (ALY2-ALY1)/(ALX2-ALX1);
        BB = ALY1 - AK*ALX1;
        XX12 = XX[0];
        YY12 = AK*XX12 + BB;
        VALUE1 = (YY12-YY[1])*(YY12-YY[0]);
        VALUE2 = (YY12-ALY1)*(YY12-ALY2);
        VALUE3 = (XX12-ALX1)*(XX12-ALX2);
        if (VALUE1 <= 0 && VALUE2 <= 0 && VALUE3 <= 0) {
            BBX = XX12;
            BBY = YY12;
        }
    }
    if (fabs(ALX2-ALX1) >= EPS && fabs(XX[1]-XX[0]) >= EPS) {
        AK = (ALY2-ALY1)/(ALX2-ALX1);
        AK12 = (YY[1]-YY[0])/(XX[1]-XX[0]);
        if (fabs(AK12-AK) >= EPS) {
            B12 = YY[0] - AK12*XX[0];
            BB = ALY1 - AK*ALX1;
            XX13 = (BB-B12)/(AK12-AK);
            T = XX13;
            YY13 = AK*T + BB;
            VALUE1 = (XX13-XX[1])*(XX13-XX[0]);
            VALUE2 = (YY13-ALY1)*(YY13-ALY2);
            VALUE3 = (XX13-ALX1)*(XX13-ALX2);
            if (VALUE1 <= 0 && VALUE2 <= 0 && VALUE3 <= 0) {
                BBX = XX13;
                BBY = YY13;
            }
        }
    }
}