int judge(Circle E,Segment S)//判断圆与线的交点
{
double a,b,c,d,e,f,g,h,lex,ley,rix,riy;
int i,j;
i=0;
j=0;
a=sub(S.p1,S.p2);
b = 2*((S.p1.x-E.p.x)*(S.p2.x-S.p1.x) + (S.p1.y-E.p.y)*(S.p2.y-S.p1.y));
c = (S.p1.x-E.p.x)*(S.p1.x-E.p.x) + (S.p1.y-E.p.y)*(S.p1.y-E.p.y) - E.r*E.r;
d = b*b - 4*a*c;
//printf("d=%lf\n",d);
if (d < 0)return 0;
else if(a==0)return 0;
else
{
lex= ((-b+sqrt(d)) / (2*a));
rix= ((-b-sqrt(d)) / (2*a));
if(lex==rix)
{
e=S.p1.x+(S.p2.x-S.p1.x)*lex;
I0->x=e;
f=S.p1.y+(S.p2.y-S.p1.y)*lex;
I0->y=f;
if(on_segment(S,*I0))return 1;
else return 0;
}
else
{
e=S.p1.x+(S.p2.x-S.p1.x)*lex;
I0->x=e;
f=S.p1.y+(S.p2.y-S.p1.y)*lex;
I0->y=f;
g=S.p1.x+(S.p2.x-S.p1.x)*rix;
I1->x=g;
h=S.p1.y+(S.p2.y-S.p1.y)*rix;
I1->y=h;
if(on_segment(S,*I0))i=1;
if(on_segment(S,*I1))j=1;
if(i&&j)return 2;
if(i&&!j)return 1;
if(!i&&j)
{
*I0=*I1;
return 1;
}
return 0;
}
}
}
/* true se os segmentos ab e cd intercedem */
bool segments_intersect(point a, point b, point c, point d) {
int d1 = direction(c, d, a);
int d2 = direction(c, d, b);
int d3 = direction(a, b, c);
int d4 = direction(a, b, d);
if(((d1 > 0 && d2 < 0) || (d1 < 0 && d2 > 0))
&& ((d3 > 0 && d4 < 0) || (d3 < 0 && d4 > 0))) return true;
if(d1 == 0 && on_segment(c, d, a)) return true;
if(d2 == 0 && on_segment(c, d, b)) return true;
if(d3 == 0 && on_segment(a, b, c)) return true;
if(d4 == 0 && on_segment(a, b, d)) return true;
return false;
}
bool intersect2D_2Segments(Segment s1,Segment s2)//求线的交点
{
Vector u,v,w;
u.x= s1.p2.x-s1.p1.x;
u.y= s1.p2.y-s1.p1.y;
v.x= s2.p2.x-s2.p1.x;
v.y= s2.p2.y-s2.p1.y;
w.x= s1.p1.x-s2.p1.x;
w.y= s1.p1.y-s2.p1.y;
double D = perp(v,u);
if (fabs(D) < SMALL_NUM)// S1 and S2 are parallel
return 0; // they are NOT collinear
double sI=perp(w,v)/D;
I0->x=s1.p1.x+u.x*sI;
I0->y=s1.p1.y+u.y*sI;
if(on_segment(s1,*I0)&&on_segment(s2,*I0)) return 1;//判断交点是否在两条线上
else return 0;
}
bool intersect(Segment const & s1, Segment const & s2) {
int d1 = direct(s2, s1.p1);
int d2 = direct(s2, s1.p2);
int d3 = direct(s1, s2.p1);
int d4 = direct(s1, s2.p2);
if (d1 * d2 == -1 && d3 * d4 == -1) {
return true;
} else if (d1 == 0 && on_segment(s2, s1.p1)) {
return true;
} else if (d2 == 0 && on_segment(s2, s1.p2)) {
return true;
} else if (d3 == 0 && on_segment(s1, s2.p1)) {
return true;
} else if (d4 == 0 && on_segment(s1, s2.p2)) {
return true;
} else {
return false;
}
}
