bool Mesh::verify_same_direction(Mesh::Face current_face, Point3D vertices[],
Point3D& point, Vector3D& normal)
{
bool is_same_direction = false;
// Make sure the intersect face is pointing to the same direction
for (unsigned int i = 0; i < current_face.size(); i++) {
is_same_direction =
((vertices[(i + 1) % current_face.size()] - vertices[i]).cross(
point - vertices[i]).dot(normal)) >= 0;
if (!is_same_direction) {
break;
}
}
return is_same_direction;
}
bool Mesh::faceIntersection(
const Ray& ray, HitRecord* hitRecord, const Mesh::Face& face) {
// Get a point on the plane
Vector3D norm;
double t;
{
const auto& p0 = m_verts[face[0]];
const auto& p1 = m_verts[face[1]];
const auto& p2 = m_verts[face[face.size()-1]];
norm = (p1 - p0).cross(p2 - p0);
auto rayNorm = ray.dir.dot(norm);
// Parallel
if (isZero(rayNorm)) return false;
t = (p0 - ray.start).dot(norm) / rayNorm;
// No intersection
if (t < 0 || isZero(t)) {
return false;
}
}
// Intersection point
auto planePt = ray.at(t);
// Now check if planePt is "left" of everything
for (size_t i = 0; i < face.size(); ++i) {
// Go over points in order
const auto& p1 = m_verts[face[i]];
const auto& p2 = m_verts[face[(i + 1) % face.size()]];
// from p1 to p2
const auto side = p2 - p1;
// cross from p1 to plane pt and dot against normal
auto k = norm.dot(side.cross(planePt - p1));
if (!isZero(k) && k < 0) {
// Zero means on the side; negative means opposite dir from norm
return false;
}
}
// Update if this is a better t value
return hitRecord->update(norm, planePt, t);
}