rtiow: print BVH stats.

rtiow/renderer/src/bvh_triangles.rs

@@ -136,6 +136,44 @@ where
             "BVHTriangles build time {:0.3}s",
             now.elapsed().as_secs_f32()
         );
+        struct Stats {
+            nodes: usize,
+            leafs: usize,
+            min_tris: u32,
+            max_tris: u32,
+        }
+        impl Default for Stats {
+            fn default() -> Self {
+                Stats {
+                    nodes: 0,
+                    leafs: 0,
+                    min_tris: u32::MAX,
+                    max_tris: u32::MIN,
+                }
+            }
+        }
+        let stats = bvh.bvh_nodes.iter().fold(Stats::default(), |mut stats, n| {
+            stats.nodes += 1;
+            if n.is_leaf() {
+                stats.leafs += 1;
+                stats.min_tris = n.tri_count.min(stats.min_tris);
+                stats.max_tris = n.tri_count.max(stats.max_tris);
+            }
+            stats
+        });
+        info!("BVHTriangles build stats:");
+        info!("  Nodes:   {}", stats.nodes);
+        info!("  Leaves:  {}", stats.leafs);
+        info!("  Min Tri: {}", stats.min_tris);
+        info!("  Max Tri: {}", stats.max_tris);
+        info!("  Avg Tri: {}", bvh.triangles.len() / stats.leafs);
+        info!("  Predict: {}", bvh.bvh_nodes.capacity());
+        info!("  Actual:  {}", bvh.bvh_nodes.len());
+        info!(
+            "  Savings:  {}",
+            (bvh.bvh_nodes.capacity() - bvh.bvh_nodes.len()) * std::mem::size_of::<BVHNode>()
+        );
+        bvh.bvh_nodes.shrink_to_fit();
         bvh
     }
 
@@ -193,7 +231,7 @@ where
                 }
             }
             // Stop subdividing if it isn't getting any better.
-            if best_cost <= parent_cost {
+            if best_cost >= parent_cost {
                 return;
             }