計算幾何：非規範相交模板

非規範相交的模板

 

int segcross(point a,point b,point c,point d)
{
 double s1,s2,s3,s4;
 int d1,d2,d3,d4;
 d1=dblcmp(s1=cross(a,b,c));
 d2=dblcmp(s2=cross(a,b,d));
 d3=dblcmp(s3=cross(c,d,a));
 d4=dblcmp(s4=cross(c,d,b));
 if((d1^d2)==-2&&(d3^d4)==-2) //規範相交
 {
    p.x=(c.x*s2-d.x*s1)/(s2-s1);
    p.y=(c.y*s2-d.y*s1)/(s2-s1);
    return 1;
 }
 if(d1==0&&dblcmp(c,a,b)<=0||
    d2==0&&dblcmp(d,a,b)<=0||
    d3==0&&dblcmp(a,c,d)<=0||
    d4==0&&dblcmp(b,c,d)<=0) return 2;
 return 0;
}