void OrbitCamera::Init(const vec3f& p, const vec3f& t) {
const vec3f v = (t - p);
const vec3f w = v.norm3D();
const float d = v.len3D();
// acosf() takes values in [-1.0, 1.0]
const float e = RAD2DEG(acosf(v.len2D() / d));
const float r = RAD2DEG(acosf(w.dot2D(XVECf)));
// when v is parallel to world z-axis, dot
// with x-axis will be 0 and rotation then
// is ambiguous (can be +90 or -90): check
// the sign of v.z to determine if we are
// looking down +z or -z
distance = cDistance = d;
elevation = cElevation = e;
rotation = cRotation = (v.z > 0.0f)? 180.0f + r: 180.0f - r;
cen = t;
active = false;
}
