From 3b85b60a62f6d2788c3c4a54f65c0aee2850eef1 Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Mon, 27 Jun 2016 21:01:18 -0700
Subject: [PATCH] Implemented occlusion rays.

This is prep for lighting support: occlusion rays are useful for
speedier shadow tests.
---
 src/bvh.rs                   |  2 ++
 src/camera.rs                |  2 +-
 src/ray.rs                   | 43 ++++++++++++++++++++++++++++++------
 src/surface/triangle_mesh.rs | 21 +++++++++++-------
 4 files changed, 52 insertions(+), 16 deletions(-)

diff --git a/src/bvh.rs b/src/bvh.rs
index 6a6c32a..443e787 100644
--- a/src/bvh.rs
+++ b/src/bvh.rs
@@ -192,6 +192,7 @@ impl BVH {
             match self.nodes[i_stack[stack_ptr]] {
                 BVHNode::Internal { bounds_range: br, second_child_index, split_axis } => {
                     let part = partition(&mut rays[..ray_i_stack[stack_ptr]], |r| {
+                        (!r.is_done()) &&
                         lerp_slice(&self.bounds[br.0..br.1], r.time).intersect_accel_ray(r)
                     });
                     if part > 0 {
@@ -210,6 +211,7 @@ impl BVH {
 
                 BVHNode::Leaf { bounds_range: br, object_range } => {
                     let part = partition(&mut rays[..ray_i_stack[stack_ptr]], |r| {
+                        (!r.is_done()) &&
                         lerp_slice(&self.bounds[br.0..br.1], r.time).intersect_accel_ray(r)
                     });
                     if part > 0 {
diff --git a/src/camera.rs b/src/camera.rs
index 35100c9..a5cd4b6 100644
--- a/src/camera.rs
+++ b/src/camera.rs
@@ -76,7 +76,7 @@ impl Camera {
                               1.0)
             .normalized();
 
-        Ray::new(orig * transform, dir * transform, time)
+        Ray::new(orig * transform, dir * transform, time, false)
     }
 }
 
diff --git a/src/ray.rs b/src/ray.rs
index 108b142..e4f905f 100644
--- a/src/ray.rs
+++ b/src/ray.rs
@@ -5,6 +5,9 @@ use std;
 use float4::Float4;
 use math::{Vector, Point, Matrix4x4};
 
+const OCCLUSION_FLAG: u32 = 1;
+const DONE_FLAG: u32 = 1 << 1;
+
 #[derive(Debug, Copy, Clone)]
 pub struct Ray {
     pub orig: Point,
@@ -15,13 +18,23 @@ pub struct Ray {
 }
 
 impl Ray {
-    pub fn new(orig: Point, dir: Vector, time: f32) -> Ray {
-        Ray {
-            orig: orig,
-            dir: dir,
-            max_t: std::f32::INFINITY,
-            time: time,
-            flags: 0,
+    pub fn new(orig: Point, dir: Vector, time: f32, is_occ: bool) -> Ray {
+        if !is_occ {
+            Ray {
+                orig: orig,
+                dir: dir,
+                max_t: std::f32::INFINITY,
+                time: time,
+                flags: 0,
+            }
+        } else {
+            Ray {
+                orig: orig,
+                dir: dir,
+                max_t: 1.0,
+                time: time,
+                flags: OCCLUSION_FLAG,
+            }
         }
     }
 
@@ -29,6 +42,10 @@ impl Ray {
         self.orig = self.orig * *mat;
         self.dir = self.dir * *mat;
     }
+
+    pub fn is_occlusion(&self) -> bool {
+        (self.flags & OCCLUSION_FLAG) != 0
+    }
 }
 
 
@@ -63,4 +80,16 @@ impl AccelRay {
         self.orig = wr.orig * *mat;
         self.dir_inv = Vector { co: Float4::new(1.0, 1.0, 1.0, 1.0) / (wr.dir * *mat).co };
     }
+
+    pub fn is_occlusion(&self) -> bool {
+        (self.flags & OCCLUSION_FLAG) != 0
+    }
+
+    pub fn is_done(&self) -> bool {
+        (self.flags & DONE_FLAG) != 0
+    }
+
+    pub fn mark_done(&mut self) {
+        self.flags |= DONE_FLAG;
+    }
 }
diff --git a/src/surface/triangle_mesh.rs b/src/surface/triangle_mesh.rs
index a302b8b..50dceaf 100644
--- a/src/surface/triangle_mesh.rs
+++ b/src/surface/triangle_mesh.rs
@@ -78,14 +78,19 @@ impl Surface for TriangleMesh {
                 let tri = (tri.0 * mat_inv, tri.1 * mat_inv, tri.2 * mat_inv);
                 if let Some((t, tri_u, tri_v)) = triangle::intersect_ray(wr, tri) {
                     if t < r.max_t {
-                        isects[r.id as usize] = SurfaceIntersection::Hit {
-                            t: t,
-                            pos: wr.orig + (wr.dir * t),
-                            nor: Normal::new(0.0, 0.0, 0.0), // TODO
-                            local_space: mat_space,
-                            uv: (tri_u, tri_v),
-                        };
-                        r.max_t = t;
+                        if r.is_occlusion() {
+                            isects[r.id as usize] = SurfaceIntersection::Occlude;
+                            r.mark_done();
+                        } else {
+                            isects[r.id as usize] = SurfaceIntersection::Hit {
+                                t: t,
+                                pos: wr.orig + (wr.dir * t),
+                                nor: Normal::new(0.0, 0.0, 0.0), // TODO
+                                local_space: mat_space,
+                                uv: (tri_u, tri_v),
+                            };
+                            r.max_t = t;
+                        }
                     }
                 }
             }