From 655c16542de4bdcaaef9b976b354f357fde3f195 Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Tue, 5 Jan 2016 07:44:37 -0800
Subject: [PATCH] Implemented basic deformation motion blur for triangles.

Not 100% happy with the interface of the BVH building yet, and
there are still some missing features as well.  But it's a start!
---
 src/lerp.rs                  | 22 +++++++++++++++++++++-
 src/main.rs                  |  8 ++++----
 src/surface/triangle_mesh.rs | 32 ++++++++++++++++++++++----------
 3 files changed, 47 insertions(+), 15 deletions(-)

diff --git a/src/lerp.rs b/src/lerp.rs
index 87c6067..fdd8e26 100644
--- a/src/lerp.rs
+++ b/src/lerp.rs
@@ -23,7 +23,7 @@ pub fn lerp_slice<T: Lerp + Copy>(s: &[T], alpha: f32) -> T {
     debug_assert!(alpha >= 0.0);
     debug_assert!(alpha <= 1.0);
 
-    if alpha == 1.0 || s.len() == 1 {
+    if s.len() == 1 || alpha == 1.0 {
         return *s.last().unwrap();
     } else {
         let tmp = alpha * ((s.len() - 1) as f32);
@@ -35,6 +35,26 @@ pub fn lerp_slice<T: Lerp + Copy>(s: &[T], alpha: f32) -> T {
     }
 }
 
+pub fn lerp_slice_with<T, F>(s: &[T], alpha: f32, f: F) -> T
+    where T: Copy,
+          F: Fn(T, T, f32) -> T
+{
+    debug_assert!(s.len() > 0);
+    debug_assert!(alpha >= 0.0);
+    debug_assert!(alpha <= 1.0);
+
+    if s.len() == 1 || alpha == 1.0 {
+        return *s.last().unwrap();
+    } else {
+        let tmp = alpha * ((s.len() - 1) as f32);
+        let i1 = tmp as usize;
+        let i2 = i1 + 1;
+        let alpha2 = tmp - (i1 as f32);
+
+        return f(s[i1], s[i2], alpha2);
+    }
+}
+
 
 impl Lerp for f32 {
     fn lerp(self, other: f32, alpha: f32) -> f32 {
diff --git a/src/main.rs b/src/main.rs
index 81918c4..4ba409c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -74,7 +74,7 @@ fn main() {
     println!("Ray size: {} bytes", mem::size_of::<Ray>());
 
     // Generate a scene of triangles
-    let mesh = TriangleMesh::from_triangles(1, {
+    let mesh = TriangleMesh::from_triangles(2, {
         let mut triangles = Vec::new();
         let xres = 32;
         let yres = 32;
@@ -92,9 +92,9 @@ fn main() {
                 triangles.push((Point::new(cx, cy, cz + 1.0),
                                 Point::new(cx + xinc, cy, cz + 1.1),
                                 Point::new(cx, cy + yinc, cz + 1.2)));
-                triangles.push((Point::new(cx + xinc, cy + yinc, cz + 1.0),
-                                Point::new(cx, cy + yinc, cz + 1.1),
-                                Point::new(cx + xinc, cy, cz + 1.2)));
+                triangles.push((Point::new(cx + 25.0, cy, cz + 1.0),
+                                Point::new(cx + 25.0 + xinc, cy, cz + 1.1),
+                                Point::new(cx + 25.0, cy + yinc, cz + 1.2)));
             }
         }
         triangles
diff --git a/src/surface/triangle_mesh.rs b/src/surface/triangle_mesh.rs
index 9796ffd..6106499 100644
--- a/src/surface/triangle_mesh.rs
+++ b/src/surface/triangle_mesh.rs
@@ -1,5 +1,6 @@
 #![allow(dead_code)]
 
+use lerp::{lerp, lerp_slice_with};
 use math::{Point, Normal, Matrix4x4};
 use ray::Ray;
 use triangle;
@@ -11,27 +12,31 @@ use super::{Surface, SurfaceIntersection};
 pub struct TriangleMesh {
     time_samples: usize,
     geo: Vec<(Point, Point, Point)>,
+    indices: Vec<usize>,
     accel: BVH,
 }
 
 impl TriangleMesh {
     pub fn from_triangles(time_samples: usize,
-                          mut triangles: Vec<(Point, Point, Point)>)
+                          triangles: Vec<(Point, Point, Point)>)
                           -> TriangleMesh {
         assert!(triangles.len() % time_samples == 0);
-        // let mut indices: Vec<usize> = (0 .. (triangles.len() / time_samples)).collect();
+        let mut indices: Vec<usize> = (0..(triangles.len() / time_samples))
+                                          .map(|n| n * time_samples)
+                                          .collect();
 
-        let accel = BVH::from_objects(&mut triangles[..], 3, |tri, bounds| {
-            // for tri in &triangles[i..(i+time_samples)] {
-            let minimum = tri.0.min(tri.1.min(tri.2));
-            let maximum = tri.0.max(tri.1.max(tri.2));
-            bounds.push(BBox::from_points(minimum, maximum));
-            // }
+        let accel = BVH::from_objects(&mut indices[..], 3, |tri_i, bounds| {
+            for tri in &triangles[*tri_i..(*tri_i + time_samples)] {
+                let minimum = tri.0.min(tri.1.min(tri.2));
+                let maximum = tri.0.max(tri.1.max(tri.2));
+                bounds.push(BBox::from_points(minimum, maximum));
+            }
         });
 
         TriangleMesh {
             time_samples: time_samples,
             geo: triangles,
+            indices: indices,
             accel: accel,
         }
     }
@@ -40,9 +45,16 @@ impl TriangleMesh {
 
 impl Surface for TriangleMesh {
     fn intersect_rays(&self, rays: &mut [Ray], isects: &mut [SurfaceIntersection]) {
-        self.accel.traverse(&mut rays[..], &self.geo, |tri, rs| {
+        self.accel.traverse(&mut rays[..], &self.indices, |tri_i, rs| {
             for r in rs {
-                if let Some((t, tri_u, tri_v)) = triangle::intersect_ray(r, *tri) {
+                let tri = lerp_slice_with(&self.geo[*tri_i..(*tri_i + self.time_samples)],
+                                          r.time,
+                                          |a, b, t| {
+                                              (lerp(a.0, b.0, t),
+                                               lerp(a.1, b.1, t),
+                                               lerp(a.2, b.2, t))
+                                          });
+                if let Some((t, tri_u, tri_v)) = triangle::intersect_ray(r, tri) {
                     if t < r.max_t {
                         isects[r.id as usize] = SurfaceIntersection::Hit {
                             t: t,