From 92fd83a7667fe13f339405e3b85493b23ade9a7c Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Sun, 16 Apr 2017 17:22:51 -0700
Subject: [PATCH] Actually using the None match arm in BVH4 traversal now.

It seems to maybe be just a hair faster.  But, also, it sets the
code up to try some more optimizations.
---
 src/accel/bvh4.rs | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/accel/bvh4.rs b/src/accel/bvh4.rs
index 79b338e..0c33f4d 100644
--- a/src/accel/bvh4.rs
+++ b/src/accel/bvh4.rs
@@ -108,6 +108,8 @@ impl<'a> BVH4<'a> {
                             let noc3 = (node_order_code >> 4) & 3;
                             let noc4 = (node_order_code >> 6) & 3;
 
+                            let mut all_hits = 0;
+
                             // Ray testing
                             let part = partition(&mut rays[..ray_i_stack[stack_ptr]], |r| {
                                 if (!r.is_done()) && (first_loop || r.trav_stack.pop()) {
@@ -115,6 +117,8 @@ impl<'a> BVH4<'a> {
                                         .intersect_accel_ray(r)
                                         .to_bitmask();
 
+                                    all_hits |= hits;
+
                                     if hits != 0 {
                                         // Push hit bits onto ray's traversal stack
                                         let shuffled_hits = match children.len() {
@@ -142,9 +146,13 @@ impl<'a> BVH4<'a> {
                             if part > 0 {
                                 for i in 0..children.len() {
                                     let inv_i = (children.len() - 1) - i;
-                                    node_stack[stack_ptr + i] =
-                                        Some(&children[((node_order_code >> (inv_i * 2)) & 3) as
-                                              usize]);
+                                    let child_i = ((node_order_code >> (inv_i * 2)) & 3) as usize;
+                                    node_stack[stack_ptr + i] = if ((all_hits >> child_i) & 1) ==
+                                                                   0 {
+                                        None
+                                    } else {
+                                        Some(&children[child_i])
+                                    };
                                     ray_i_stack[stack_ptr + i] = part;
                                 }