From b1bd419779831a812840ea7f16f37f0d7965a9ba Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Thu, 17 Aug 2017 11:23:47 -0700
Subject: [PATCH] Factored out interpolating over a triangle's surface into its
 own function.

We'll be using this in the RectangleLight sampling code soon.
---
 src/surface/triangle.rs      | 16 ++++++++++++++++
 src/surface/triangle_mesh.rs | 11 +----------
 2 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/src/surface/triangle.rs b/src/surface/triangle.rs
index f19b6e2..1f785a4 100644
--- a/src/surface/triangle.rs
+++ b/src/surface/triangle.rs
@@ -128,6 +128,22 @@ pub fn intersect_ray(ray: &Ray, tri: (Point, Point, Point)) -> Option<(f32, f32,
     Some((t, b0, b1, b2))
 }
 
+/// Calculates a point on a triangle's surface at the given barycentric
+/// coordinates.
+///
+/// Returns the point and the error magnitude of the point.
+pub fn surface_point(tri: (Point, Point, Point), bary: (f32, f32, f32)) -> (Point, f32) {
+    let pos = ((tri.0.into_vector() * bary.0) + (tri.1.into_vector() * bary.1) +
+                   (tri.2.into_vector() * bary.2))
+        .into_point();
+
+    let pos_err = (((tri.0.into_vector().abs() * bary.0) + (tri.1.into_vector().abs() * bary.1) +
+                        (tri.2.into_vector().abs() * bary.2)) * fp_gamma(7)).co
+        .h_max();
+
+    (pos, pos_err)
+}
+
 fn max_abs_3(a: f32, b: f32, c: f32) -> f32 {
     let a = a.abs();
     let b = b.abs();
diff --git a/src/surface/triangle_mesh.rs b/src/surface/triangle_mesh.rs
index 3f46e60..29c8ca5 100644
--- a/src/surface/triangle_mesh.rs
+++ b/src/surface/triangle_mesh.rs
@@ -5,7 +5,6 @@ use mem_arena::MemArena;
 use accel::BVH4;
 use bbox::BBox;
 use boundable::Boundable;
-use fp_utils::fp_gamma;
 use lerp::lerp_slice;
 use math::{Point, Normal, Matrix4x4, dot, cross};
 use ray::{Ray, AccelRay};
@@ -193,15 +192,7 @@ impl<'a> Surface for TriangleMesh<'a> {
                                 r.mark_done();
                             } else {
                                 // Calculate intersection point and error magnitudes
-                                let pos = ((tri.0.into_vector() * b0) + (tri.1.into_vector() * b1) +
-                                               (tri.2.into_vector() * b2))
-                                    .into_point();
-
-                                let pos_err = (((tri.0.into_vector().abs() * b0) +
-                                                    (tri.1.into_vector().abs() * b1) +
-                                                    (tri.2.into_vector().abs() * b2)) *
-                                                   fp_gamma(7)).co
-                                    .h_max();
+                                let (pos, pos_err) = triangle::surface_point(tri, (b0, b1, b2));
 
                                 // Calculate geometric surface normal
                                 let geo_normal = cross(tri.0 - tri.1, tri.0 - tri.2).into_normal();