//获取一条向量与矩形交点,0没有交点，1有一个交点，2有两个交点
- (CGPoint*)getIntersectionPointWithLine:(CGPoint)start end:(CGPoint)end andRect:(CGRect)rect {
    //初始化一个数组保存结果
    CGPoint *result = malloc(sizeof(CGPoint)*4);
    result[0] = CGPointMake(-1, -1);
    result[1] = CGPointMake(-1, -1);
    result[2] = CGPointMake(-1, -1);
    result[3] = CGPointMake(-1, -1);

    CGFloat ox = rect.origin.x;
    CGFloat oy = rect.origin.y;
    CGFloat ow = rect.size.width;
    CGFloat oh = rect.size.height;
    
    CGPoint lt = CGPointMake(ox, oy);
    CGPoint rt = CGPointMake(ox + ow, oy);
    CGPoint lb = CGPointMake(ox, oy + oh);
    CGPoint rb = CGPointMake(ox + ow, oy + oh);
    
    CGPoint top = [self getIntersectionPointWithL1p1:start l1p2:end l2p1:lt l2p2:rt];
    CGPoint left = [self getIntersectionPointWithL1p1:start l1p2:end l2p1:lt l2p2:lb];
    CGPoint bottom = [self getIntersectionPointWithL1p1:start l1p2:end l2p1:lb l2p2:rb];
    CGPoint right = [self getIntersectionPointWithL1p1:start l1p2:end l2p1:rt l2p2:rb];
    
    int count = 0;
    if (top.x != -1 && top.y != -1) {
        result[count++] = top;
    }
    if (left.x != -1 && left.y != -1) {
        result[count++] = left;
    }
    if (right.x != -1 && right.y != -1) {
        result[count++] = right;
    }
    if (bottom.x != -1 && bottom.y != -1) {
        result[count++] = bottom;
    }
    
    return result;
}

//获取两条线的交点
- (CGPoint)getIntersectionPointWithL1p1:(CGPoint)point1 l1p2:(CGPoint)point2 l2p1:(CGPoint)point3 l2p2:(CGPoint)point4 {
    //A1x+B1y+C1 = 0 A2x+B2y+C2 = 0
    float A1,B1,C1,A2,B2,C2;
    getABCFunWith(point1.x, point1.y, point2.x, point2.y, &A1, &B1, &C1);
    getABCFunWith(point3.x, point3.y, point4.x, point4.y, &A2, &B2, &C2);
    
    //交点
    float x = FLT_MIN,y = FLT_MIN;
    getPointOfTwoLine(A1, B1, C1, A2, B2, C2, &x, &y);
    if (x != FLT_MIN && y != FLT_MIN) {
        
    }
    
//    return CGPointMake(x, y); //如果不用判断是否在线段内则直接return
    
    //判断是否在两个线段上，第3，4点为rect的边界
//    BOOL inLine1 = judegePointInLine(x, y, point1.x, point1.y, point2.x, point2.y);
    BOOL inLine2 = judegePointInLine(x, y, point3.x, point3.y, point4.x, point4.y);

    if (inLine2) {
        return CGPointMake(x, y);
    } else {
        return CGPointMake(-1, -1);
    }
}

//判断是否在线段内
bool judegePointInLine(float px,float py , float p1x,float p1y,float p2x,float p2y) {
    float minL1x = MIN(p1x, p2x);
    float maxL1x = MAX(p1x, p2x);
    float minL1y = MIN(p1y, p2y);
    float maxL1y = MAX(p1y, p2y);
    if (px < minL1x || px > maxL1x || py < minL1y || py > maxL1y) {
        return false;
    } else {
        return true;
    }
}

//获取两条线的交点坐标 输入两条直线点一般式方程
void getPointOfTwoLine(float a1,float b1 ,float c1, float a2 ,float b2 ,float c2, float *x ,float *y) {
    if (a1*b2 == a2*b1) { //平行
        return;
    }
    if (a1/a2 == b1/b2 && a1/a2 == c1/c2 && b1/b2 == c1/c2) { //重合
        return;
    }
    *x = (c1 * b2 - c2 * b1) / (a2 * b1 - a1 * b2);
    *y = (a2 * c1 - a1 * c2) / (a1 * b2 - a2 * b1);
    NSLog(@"x = %f  y = %f",*x,*y);
}

//一般式方程 Ax+By+C=0 (y2-y1)x + (x1-x2)y +x2y1 -x1y2 = 0 , A = Y2 - Y1 B = X1 - X2  C = X2*Y1 - X1*Y2
void getABCFunWith(float x1,float y1,float x2,float y2,float* a ,float* b,float* c) {
    *a = y2 - y1;
    *b = x1 - x2;
    *c = x2*y1 - x1*y2;
    NSLog(@"a = %f b = %f c = %f",*a,*b,*c);
}