[算法]直线与圆的交点程序设计

/** * Created by apple on 2017/1/15. */
//求直线与圆的交点
/*函数参数说明: cx:圆X轴坐标 cy:圆y轴坐标 r:圆半径 stx:起点直线的X轴坐标 sty:起点直线的轴坐标 edx:终点直线的X轴坐标 edy:终点直线的Y轴坐标 返回值:交点坐标(x,y) */
function  getPoint(cx,cy,r,stx,sty,edx,edy) {
   // 求直线
    var k = (edy - sty) / (edx - stx);
    var b = edy - k*edx;
    //列方程
    var x1,y1,x2,y2;
    var c = cx*cx + (b - cy)*(b- cy) -r*r;
    var a = (1 + k*k);
    var b1 = (2*cx - 2*k*(b - cy));

    var  tmp = Math.sqrt(b1*b1 - 4*a*c);
    x1 = ( b1 + tmp )/(2*a);
    y1 = k*x1 + b;
    x2 = ( b1 - tmp)/(2*a);
    y2 = k*x2 + b;
//判断求出的点是否在圆上
    var res = (x1 -cx)*(x1 -cx) + (y1 - cy)*(y1 -cy);
    var  p = {};
    if( res == r*r)
    {

        p.x = x1;
        p.y = y1;
    }    else
    {
        p.x = x2;
        p.y = y2;
    }
return p;
}
//测试
var s = getPoint(10,20,50,34,45,12,34);
// 结果:{x: 48.2952871010182, y: 52.1476435505091}
console.log(s);