From 450342c3d4fe97ba97528c9bccfa3f4fac4a8dab Mon Sep 17 00:00:00 2001
From: Bill Thiede <git@xinu.tv>
Date: Sun, 12 Feb 2023 13:14:02 -0800
Subject: [PATCH] rtiow: BVHTriangles refactor part of subdivide into
 find_best_split_plane.

---
 rtiow/renderer/src/bvh_triangles.rs | 61 +++++++++++++++++------------
 1 file changed, 36 insertions(+), 25 deletions(-)

diff --git a/rtiow/renderer/src/bvh_triangles.rs b/rtiow/renderer/src/bvh_triangles.rs
index 1a9441e..91b4f71 100644
--- a/rtiow/renderer/src/bvh_triangles.rs
+++ b/rtiow/renderer/src/bvh_triangles.rs
@@ -97,6 +97,12 @@ where
     }
 }
 
+struct SplitCost {
+    pos: f32,
+    axis: usize,
+    cost: f32,
+}
+
 const ROOT_NODE_IDX: usize = 0;
 impl<M> BVHTriangles<M>
 where
@@ -206,6 +212,30 @@ where
         }
         node.aabb = AABB::new(aabb_min, aabb_max);
     }
+
+    fn find_best_split_plane(&self, node: &BVHNode) -> SplitCost {
+        let mut best_axis = usize::MAX;
+        let mut best_pos = 0.;
+        let mut best_cost = f32::MAX;
+
+        for axis in 0..3 {
+            for i in 0..node.tri_count {
+                let triangle = &self.triangles[self.triangle_index[(node.left_first + i) as usize]];
+                let candidate_pos = triangle.centroid[axis];
+                let cost = self.evaluate_sah(node, axis, candidate_pos);
+                if cost <= best_cost {
+                    best_pos = candidate_pos;
+                    best_axis = axis;
+                    best_cost = cost;
+                }
+            }
+        }
+        SplitCost {
+            pos: best_pos,
+            cost: best_cost,
+            axis: best_axis,
+        }
+    }
     fn subdivide(&mut self, idx: usize) {
         let node = &self.bvh_nodes[idx];
         let parent_area = node.aabb.area();
@@ -213,37 +243,18 @@ where
 
         let (left_first, tri_count, left_count, i) = {
             let node = &self.bvh_nodes[idx];
-
-            let mut best_axis = usize::MAX;
-            let mut best_pos = 0.;
-            let mut best_cost = f32::MAX;
-
-            for axis in 0..3 {
-                for i in 0..node.tri_count {
-                    let triangle =
-                        &self.triangles[self.triangle_index[(node.left_first + i) as usize]];
-                    let candidate_pos = triangle.centroid[axis];
-                    let cost = self.evaluate_sah(node, axis, candidate_pos);
-                    if cost <= best_cost {
-                        best_pos = candidate_pos;
-                        best_axis = axis;
-                        best_cost = cost;
-                    }
-                }
-            }
+            let split = self.find_best_split_plane(&node);
             // Stop subdividing if it isn't getting any better.
-            if best_cost >= parent_cost {
+            if split.cost >= parent_cost {
                 return;
             }
 
-            let axis = best_axis;
-            let split_pos = best_pos;
-
             // Split the group in two halves.
             let mut i = node.left_first as isize;
             let mut j = i + node.tri_count as isize - 1;
             while i <= j {
-                if self.triangles[self.triangle_index[i as usize]].centroid[axis] < split_pos {
+                if self.triangles[self.triangle_index[i as usize]].centroid[split.axis] < split.pos
+                {
                     i += 1;
                 } else {
                     self.triangles.swap(
@@ -317,7 +328,7 @@ where
     }
 
     fn intersect_bvh(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
-        let mut node = &self.bvh_nodes[0];
+        let mut node = &self.bvh_nodes[ROOT_NODE_IDX];
         let mut stack = Vec::with_capacity(2);
         let mut nearest = None;
         loop {
@@ -458,7 +469,7 @@ where
     }
 
     fn bounding_box(&self, _t_min: f32, _t_max: f32) -> Option<AABB> {
-        Some(self.bvh_nodes[0].aabb)
+        Some(self.bvh_nodes[ROOT_NODE_IDX].aabb)
     }
 }