From 24cbdb5ab9c52bc09721c3c3674d2067f3fe6411 Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Thu, 30 Jun 2016 19:33:44 -0700
Subject: [PATCH] Fixed bug in ray/triangle intersection code.

It was counting intersections behind the ray.
---
 src/triangle.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/triangle.rs b/src/triangle.rs
index 3f15dd7..9b0a0e6 100644
--- a/src/triangle.rs
+++ b/src/triangle.rs
@@ -16,6 +16,11 @@ pub fn intersect_ray(ray: &Ray, tri: (Point, Point, Point)) -> Option<(f32, f32,
         let tvec = ray.orig - tri.0;
         let qvec = cross(tvec, edge1);
 
+        let t = dot(edge2, qvec) * inv_det;
+        if t < 0.0 {
+            return None;
+        }
+
         let u = dot(tvec, pvec) * inv_det;
         if u < 0.0 || u > 1.0 {
             return None;
@@ -26,7 +31,6 @@ pub fn intersect_ray(ray: &Ray, tri: (Point, Point, Point)) -> Option<(f32, f32,
             return None;
         }
 
-        let t = dot(edge2, qvec) * inv_det;
         return Some((t, u, v));
     } else {
         return None;