1 files changed, 79 insertions, 0 deletions
diff --git a/src/hittable/triangle.rs b/src/hittable/triangle.rs
new file mode 100644
index 0000000..0fe5fc4
--- /dev/null
+++ b/src/hittable/triangle.rs
@@ -0,0 +1,79 @@
+use std::sync::Arc;
+
+use crate::{hittable::{HitRecord, Hittable, AABB}, material::Material, ray::Ray, vec3::{Point3, Vec3}};
+
+pub struct Triangle {
+    pub v0: Point3,
+    pub v1: Point3,
+    pub v2: Point3,
+    pub material: Arc<dyn Material>,
+    pub custom_normal: Option<Vec3>,
+}
+
+impl Triangle {
+    fn has_vertex_at_infinity(&self) -> bool {
+        self.v0.has_infinite_member() || self.v1.has_infinite_member() || self.v2.has_infinite_member()
+    }
+}
+
+impl Hittable for Triangle {
+    // https://en.wikipedia.org/wiki/M%C3%B6ller%E2%80%93Trumbore_intersection_algorithm
+    fn hit(&self, ray: &Ray, t_min: f64, t_max: f64) -> Option<HitRecord> {
+        let epsilon: f64 = 0.0000001;
+        let edge1 = &self.v1 - &self.v0;
+        let edge2 = &self.v2 - &self.v0;
+        let h = ray.direction.cross(&edge2);
+        let a = edge1.dot(&h);
+
+        if a > -epsilon && a < epsilon {
+            return None; // This ray is parallel to the triangle.
+        }
+        let f = 1.0 / a;
+        let s = &ray.origin - &self.v0;
+        let u = f * s.dot(&h);
+        if u < 0.0 || u > 1.0 {
+            return None;
+        }
+        let q = s.cross(&edge1);
+        let v = f * ray.direction.dot(&q);
+        if v < 0.0 || u + v > 1.0 {
+            return None;
+        }
+        // At this point, we can compute the point of intersection.
+        let t = f * edge2.dot(&q);
+        if t < t_min || t > t_max {
+            return None;
+        }
+        let mut hit_record = HitRecord::new();
+        hit_record.u = u;
+        hit_record.v = v;
+        hit_record.t = t;
+        hit_record.p = ray.at(t);
+        // TODO: i don't love this, but it allows for custom surface normals from OBJ data.
+        if let Some(normal) = &self.custom_normal {
+            hit_record.set_face_normal(ray, &normal);
+        } else {
+            let outward_normal = edge2.cross(&edge1).unit_vector();
+            hit_record.set_face_normal(ray, &outward_normal);
+        }
+        hit_record.material = Some(self.material.clone());
+        Some(hit_record)
+    }
+    fn bounding_box(&self, _: f64, _: f64) -> Option<AABB> {
+        match self.has_vertex_at_infinity() {
+            true => None,
+            false => Some(AABB {
+                minimum: Point3 {
+                    x: self.v0.x.min(self.v1.x).min(self.v2.x) - 0.0001,
+                    y: self.v0.y.min(self.v1.y).min(self.v2.y) - 0.0001,
+                    z: self.v0.z.min(self.v1.z).min(self.v2.z) - 0.0001,
+                },
+                maximum: Point3 {
+                    x: self.v0.x.max(self.v1.x).max(self.v2.x) + 0.0001,
+                    y: self.v0.y.max(self.v1.y).max(self.v2.y) + 0.0001,
+                    z: self.v0.z.max(self.v1.z).max(self.v2.z) + 0.0001,                    
+                },
+            })
+        }
+    }
+}