bool intersection_point(line l1, line l2, point2d *p)
{
if (same_lineQ(l1, l2)) {
p->x = p->y = 0.0;
return true;
}
if (parallelQ(l1,l2) == true) {
return false;
}
p->x = (l2.b * l1.c - l1.b * l2.c) / (l2.a * l1.b - l1.a * l2.b);
if (fabs(l1.b) > EPSILON) // test for vertical line
p->y = - (l1.a * p->x + l1.c) / l1.b;
else
p->y = - (l2.a * p->x + l2.c) / l2.b;
return true;
}
void intersection_point(line l1, line l2, point p) {
if(same_lineQ(l1, l2)) {
printf("Warning: Identical lines, all points intersect.\n");
p[X] = p[Y] = 0.0;
return;
}
if(parallelQ(l1, l2) == TRUE) {
printf("Error: Distinct parallel lines do not intersect.\n");
return;
}
p[X] = (l2.b*l1.c - l1.b*l2.c) / (l2.a*l1.b - l1.a*l2.b);
if(fabs(l1.b) > EPSILON) /* test for vertical line */
p[Y] = - (l1.a * (p[X]) + l1.c) / l1.b;
else
p[Y] = - (l2.a * (p[X]) + l2.c) / l2.b;
}
bool segments_intersect(segment s1, segment s2) {
line l1, l2; /* lines containing the input segments */
point p; /* intersection point */
points_to_line(s1.p1, s1.p2, &l1);
points_to_line(s2.p1, s2.p2, &l2);
if(same_lineQ(l1, l2)) /* overlapping or disjoint segments */
return( point_in_box(s1.p1, s2.p1, s2.p2) ||
point_in_box(s1.p2, s2.p1, s2.p2) ||
point_in_box(s2.p1, s1.p1, s1.p2) ||
point_in_box(s2.p2, s1.p1, s1.p2) );
if(parallelQ(l1, l2)) return(FALSE);
intersection_point(l1, l2, p);
return( point_in_box(p, s1.p1, s1.p2) && point_in_box(p, s2.p1, s2.p2) );
}
bool segments_intersect(segment s1, segment s2)
{
line l1, l2;
points_to_line(s1.p1, s1.p2, &l1);
points_to_line(s2.p1, s2.p2, &l2);
if (same_lineQ(l1, l2))
return (point_in_box(s1.p1, s2.p1, s2.p2) ||
point_in_box(s1.p2, s2.p1, s2.p2) ||
point_in_box(s2.p1, s1.p1, s1.p2) ||
point_in_box(s2.p1, s1.p1, s1.p2) );
if (parallelQ(l1, l2))
return false;
point2d p; // intersection point
intersection_point(l1, l2, p);
return (point_in_box(p, s1.p1, s1.p2) && point_in_box(p, s2.p1, s2.p2) );
}
bool same_lineQ(line l1, line l2)
{
return (parallelQ(l1, l2) && (fabs(l1.c - l2.c) <= EPSILON) );
}
