Mat* create_look_at_mat(Vec* cam_pos, Vec* targ_pos, Vec* up) {
Mat* p = create_translation_mat(-cam_pos->x, -cam_pos->y, -cam_pos->z);
Vec* d = vec_minus_vec(targ_pos, cam_pos);
Vec* f = normalize_vec(d);
Vec* c1 = cross_vec(f, up);
Vec* r = normalize_vec(c1);
Vec* c2 = cross_vec(r, f);
Vec* u = normalize_vec(c2);
Mat* ori = identity_mat();
ori->m[0] = r->x;
ori->m[4] = r->y;
ori->m[8] = r->z;
ori->m[1] = u->x;
ori->m[5] = u->y;
ori->m[9] = u->z;
ori->m[2] = -f->x;
ori->m[6] = -f->y;
ori->m[10] = -f->z;
Mat* ret = mat_times_mat(ori, p);
delete_mat(p);
delete_mat(ori);
delete_vec(d);
delete_vec(f);
delete_vec(r);
delete_vec(u);
delete_vec(c1);
delete_vec(c2);
return ret;
}
/**
* Determine if one segment intersects another.
*
* @param _s1 the threshold edge
* @param _s2 the segment
* @param _i1 the possible intersection point
* @param _i2 the possible intersection point
* @return 0 if the segments do not intersect
* 1 if one segment intersects another at precisely one point
* 2 if one segment overlaps another, in which case there are two intersection points.
* @throw CException should any of the following occur:
* 1. zero v.y.
*/
unsigned short CThreshold::seg_intersection(seg& _s1, seg& _s2, pt& _i1, pt& _i2 ) {
unsigned short intersect = 0;
vec u, v, w, w2;
double d, du, dv;
double t, t0, t1;
double si, ti;
do {
init_vec(_s1.p1, _s1.p2, u);
init_vec(_s2.p1, _s2.p2, v);
init_vec(_s2.p1, _s1.p1, w);
d = cross_vec(u, v);
if (fabs(d) < PARALLELISM_TOLERANCE) {
// segments are parallel
if (cross_vec(u, w) != 0 || cross_vec(v, w) != 0) {
// not colinear
break;
}
// they are colinear or degenerate
// check if they are degenerate points
du = dot_vec(u, u);
dv = dot_vec(v, v);
if (0 == du && 0 == dv) {
// both segments are points
if (pts_equal(_s1.p1, _s2.p1)) {
// the same point
intersect = 1;
init_pt(_i1, _s1.p1);
}
break;
}
if (0 == du) {
// s1 is a single point
if (pt_within_seg(_s2, _s1.p1)) {
// is within s2
intersect = 1;
init_pt(_i1, _s1.p1);
}
break;
}
if (0 == dv) {
// s2 a single point
if (pt_within_seg(_s1, _s2.p1)) {
// is within s1
intersect = 1;
init_pt(_i1, _s2.p1);
}
break;
}
// colinear segments - get overlap (or not)
init_vec(_s2.p1, _s1.p2, w2);
if (0 != v.x) {
t0 = w.x/v.x;
t1 = w2.x/v.x;
}
else {
if (0.0 == v.y) {
throw CException("Error! Zero v.y.");
}
t0 = w.y/v.y;
t1 = w2.y/v.y;
}
// must have t0 smaller than t1
if (t0 > t1) {
// swap if not
t = t0;
t0 = t1;
t1 = t;
}
if (t0 > 1 || t1 < 0) {
break; // no overlap
}
t0 = t0 < 0 ? 0 : t0; // clip to min 0
t1 = t1 > 1 ? 1 : t1; // clip to max 1
if (t0 == t1) {
// intersection is a pt
intersect = 1;
_i1.x = _s2.p1.x + (t0*v.x);
_i1.y = _s2.p1.y + (t0*v.y);
break;
}
// they overlap in a valid subseg
intersect = 2;
_i1.x = _s2.p1.x + (t0*v.x);
_i1.y = _s2.p1.y + (t0*v.y);
_i2.x = _s2.p1.x + (t1*v.x);
_i2.y = _s2.p1.y + (t1*v.y);
break;
} // end of <if (fabs(d) < PARALLELISM_TOLERANCE)> clause
// the segs are skew and may intersect in a pt
// get the intersect parameter for s1
si = cross_vec(v, w)/d;
if (si < 0 || si > 1) {
// no intersect with s1
break;
}
// get the intersect parameter for S2
ti = cross_vec(u, w)/d;
if (ti < 0 || ti > 1) {
// no intersect with s2
break;
}
intersect = 1;
_i1.x = _s1.p1.x + (si*u.x);
_i1.y = _s1.p1.y + (si*u.y);
} while (0);
return intersect;
}