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//! Triangle representation in 3D space.
use bytemuck::{Pod, Zeroable};
use glam::{Mat4, Vec2, Vec3A, vec2};
use crate::{Boundable, Transformable, aabb::Aabb, ray::Ray};
#[derive(Clone, Copy, Default, Debug, Zeroable)]
pub struct Triangle {
pub v0: Vec3A,
pub v1: Vec3A,
pub v2: Vec3A,
}
unsafe impl Pod for Triangle {}
impl Triangle {
/// Compute the normal of the triangle geometry.
#[inline(always)]
pub fn compute_normal(&self) -> Vec3A {
let e1 = self.v1 - self.v0;
let e2 = self.v2 - self.v0;
e1.cross(e2).normalize_or_zero()
}
/// Compute the bounding box of the triangle.
#[inline(always)]
pub fn aabb(&self) -> Aabb {
Aabb::from_points(&[self.v0, self.v1, self.v2])
}
/// Find the distance (t) of the intersection of the `Ray` and this Triangle.
/// Returns f32::INFINITY for miss.
#[inline(always)]
pub fn intersect(&self, ray: &Ray) -> f32 {
// TODO not very water tight from the back side in some contexts (tris with edges at 0,0,0 show 1px gap)
// Find out if this is typical of Möller
// Based on Fast Minimum Storage Ray Triangle Intersection by T. Möller and B. Trumbore
// https://madmann91.github.io/2021/04/29/an-introduction-to-bvhs.html
let cull_backface = false;
let e1 = self.v0 - self.v1;
let e2 = self.v2 - self.v0;
let n = e1.cross(e2);
let c = self.v0 - ray.origin;
let r = ray.direction.cross(c);
let inv_det = 1.0 / n.dot(ray.direction);
let u = r.dot(e2) * inv_det;
let v = r.dot(e1) * inv_det;
let w = 1.0 - u - v;
//let hit = u >= 0.0 && v >= 0.0 && w >= 0.0;
//let valid = if cull_backface {
// inv_det > 0.0 && hit
//} else {
// inv_det != 0.0 && hit
//};
// Note: differs in that if v == -0.0, for example will cause valid to be false
let hit = u.to_bits() | v.to_bits() | w.to_bits();
let valid = if cull_backface {
(inv_det.to_bits() | hit) & 0x8000_0000 == 0
} else {
inv_det != 0.0 && hit & 0x8000_0000 == 0
};
if valid {
let t = n.dot(c) * inv_det;
if t >= ray.tmin && t <= ray.tmax {
return t;
}
}
f32::INFINITY
}
// https://github.com/RenderKit/embree/blob/0c236df6f31a8e9c8a48803dada333e9ea0029a6/kernels/geometry/triangle_intersector_moeller.h#L9
#[cfg(all(
any(target_arch = "x86", target_arch = "x86_64"),
target_feature = "sse2"
))]
pub fn intersect_embree(&self, ray: &Ray) -> f32 {
// Not watertight from the front side? Looks similar to what above looks like from the back side.
// This uses the orientation from https://madmann91.github.io/2021/04/29/an-introduction-to-bvhs.html
let cull_backface = false;
let v0 = self.v0;
let e1 = self.v0 - self.v1;
let e2 = self.v2 - self.v0;
let ng = e1.cross(e2);
// Calculate denominator
let o = ray.origin;
let d = ray.direction;
let c = v0 - o;
let r = c.cross(d);
let den = (-ng).dot(d);
let abs_den = den.abs();
fn signmsk(x: f32) -> f32 {
#[cfg(target_arch = "x86")]
use std::arch::x86::*;
#[cfg(target_arch = "x86_64")]
use std::arch::x86_64::*;
unsafe {
let mask = _mm_set1_ps(-0.0);
let x_vec = _mm_set_ss(x);
let sign_bit = _mm_and_ps(x_vec, mask);
_mm_cvtss_f32(sign_bit)
//_mm_cvtss_f32(_mm_and_ps(
// _mm_set_ss(x),
// _mm_castsi128_ps(_mm_set1_epi32(-2147483648i32)),
//))
}
}
let sgn_den = signmsk(den).to_bits();
// Perform edge tests
let u = f32::from_bits(r.dot(e2).to_bits() ^ sgn_den);
let v = f32::from_bits(r.dot(e1).to_bits() ^ sgn_den);
// TODO simd uv?
// Perform backface culling
// OG
//let valid = if cull_backface {
// den < 0.0 && u >= 0.0 && v >= 0.0 && u + v <= abs_den
//} else {
// den != 0.0 && u >= 0.0 && v >= 0.0 && u + v <= abs_den
//};
let w = abs_den - u - v;
let valid = if cull_backface {
((-den).to_bits() | u.to_bits() | v.to_bits() | (abs_den - u - v).to_bits())
& 0x8000_0000
== 0
} else {
den != 0.0 && ((u.to_bits() | v.to_bits() | w.to_bits()) & 0x8000_0000) == 0
};
if !valid {
return f32::INFINITY;
}
// Perform depth test
let t = f32::from_bits((-ng).dot(c).to_bits() ^ sgn_den);
if abs_den * ray.tmin < t && t <= abs_den * ray.tmax {
return t;
}
f32::INFINITY
}
#[inline(always)]
pub fn compute_barycentric(&self, ray: &Ray) -> Vec2 {
let e1 = self.v0 - self.v1;
let e2 = self.v2 - self.v0;
let ng = e1.cross(e2).normalize_or_zero();
let r = ray.direction.cross(self.v0 - ray.origin);
vec2(r.dot(e2), r.dot(e1)) / ng.dot(ray.direction)
}
}
impl Boundable for Triangle {
#[inline(always)]
fn aabb(&self) -> Aabb {
self.aabb()
}
}
impl Transformable for &mut Triangle {
fn transform(&mut self, matrix: &Mat4) {
self.v0 = matrix.transform_point3a(self.v0);
self.v1 = matrix.transform_point3a(self.v1);
self.v2 = matrix.transform_point3a(self.v2);
}
}
impl<T> Transformable for T
where
T: AsMut<[Triangle]>,
{
fn transform(&mut self, matrix: &Mat4) {
self.as_mut().iter_mut().for_each(|mut triangle| {
triangle.transform(matrix);
});
}
}