圆与直线的交点

圆与直线的交点

point project(point a,point b,point c)
{
    point base=b-a;
    double r=dot(base,c-a)/norm(base);
    return a+(base*r);
}

pairgetcrosspoints(point a,int r,point b,point c)
{
    point pr=project(b,c,a);
    point e=(b-c)/ABS(b-c);
    double base=sqrt(r*r*1.0-norm(pr-a));
    e=e*base;
    return make_pair(pr+e,pr-e);
}