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use hit::Hit;
use material::Material;
use ray::Ray;
use Traceable;

use cgmath::prelude::*;
extern crate cgmath;
type Float3 = cgmath::Vector3<f64>;

#[derive(Copy, Clone)]
pub struct Triangle {
    pub p0: Float3,
    pub p1: Float3,
    pub p2: Float3,
    pub normal: Float3,
    pub material: Material,
}

impl Triangle {
    // Spawn a new rectangle
    pub fn new(p0: Float3, p1: Float3, p2: Float3, material: Material) -> Triangle {
        Triangle {
            p0: p0,
            p1: p1,
            p2: p2,
            normal: (p2 - p0).normalize().cross((p1 - p0).normalize()),
            material: material,
        }
    }
}

impl Traceable for Triangle {
    // Ray-Triangle Intersection
    fn intersect(&self, r: &Ray, result: &mut Hit) -> bool {
        let p0p1 = self.p1 - self.p0;
        let p0p2 = self.p2 - self.p0;
        let pvec = r.direction.cross(p0p2);
        let det = p0p1.dot(pvec);

        // if the determinant is negative the triangle is backfacing
        // if the determinant is close to 0, the ray misses the triangle

        if det < 1e-6 {
            return false;
        }

        let tvec = r.origin - self.p0;
        let u = tvec.dot(pvec) / det;
        if u < 0.0 || u > 1.0 {
            return false;
        };

        let qvec = tvec.cross(p0p1);
        let v = r.direction.dot(qvec) / det;
        if v < 0.0 || u + v > 1.0 {
            return false;
        };

        // intersection
        result.t = p0p2.dot(qvec) / det;
        result.p = r.origin + r.direction * result.t;
        result.n = if Float3::dot(self.normal, r.direction) < 0.0 {
            self.normal
        } else {
            self.normal * -1.0
        };
        result.material = self.material;

        return true;
    }
}