rtiow: BVHTriangles use BVHNode::cost for readability.

rtiow/renderer/src/bvh_triangles.rs

@@ -27,6 +27,11 @@ impl BVHNode {
     fn is_leaf(&self) -> bool {
         self.tri_count > 0
     }
+
+    fn cost(&self) -> f32 {
+        let area = self.aabb.area();
+        self.tri_count as f32 * area
+    }
 }
 
 #[derive(Clone, PartialEq)]
@@ -236,16 +241,14 @@ where
             axis: best_axis,
         }
     }
-    fn subdivide(&mut self, idx: usize) {
-        let node = &self.bvh_nodes[idx];
-        let parent_area = node.aabb.area();
-        let parent_cost = node.tri_count as f32 * parent_area;
 
+    fn subdivide(&mut self, idx: usize) {
         let (left_first, tri_count, left_count, i) = {
             let node = &self.bvh_nodes[idx];
             let split = self.find_best_split_plane(&node);
+            let no_split_cost = node.cost();
             // Stop subdividing if it isn't getting any better.
-            if split.cost >= parent_cost {
+            if split.cost >= no_split_cost {
                 return;
             }