fix(bvh-region): get_closest now returns the correct closest element

Cargo.toml

@@ -95,6 +95,7 @@ papaya = '0.1.4'
 parking_lot = '0.12.3'
 plotters-bitmap = '0.3.6'
 proc-macro2 = '1.0.89'
+proptest = "1.5.0"
 quote = '1.0.37'
 rand = '0.8.5'
 rayon = '1.10.0'

crates/bvh-region/Cargo.toml

@@ -11,23 +11,23 @@ name = "sort"
 #name = "side_by_side"
 
 [dependencies]
-geometry = {workspace = true}
-glam = {workspace = true, features = ["serde"]}
-plotters = {workspace = true, features = [
-  "plotters-bitmap",
-  "image"
-], optional = true}
-plotters-bitmap = {workspace = true, optional = true}
-arrayvec = {workspace = true}
-fastrand = {workspace = true}
-ordered-float = {workspace = true}
-rayon = {workspace = true}
-tracing = {workspace = true}
+arrayvec = { workspace = true }
+derive_more = { workspace = true }
+fastrand = { workspace = true }
+geometry = { workspace = true }
+glam = { workspace = true, features = ["serde"] }
+ordered-float = { workspace = true }
+plotters = { workspace = true, features = ["plotters-bitmap", "image"], optional = true }
+plotters-bitmap = { workspace = true, optional = true }
+proptest = { workspace = true }
+rayon = { workspace = true }
+tracing = { workspace = true }
 
 [dev-dependencies]
-criterion = {workspace = true}
+approx = { workspace = true }
+criterion = { workspace = true }
+rand = { workspace = true }
 #divan = {workspace = true}
-rand = {workspace = true}
 #tango-bench = {workspace = true}
 
 [features]

crates/bvh-region/src/build.rs

@@ -0,0 +1,188 @@
+use std::fmt::Debug;
+
+use geometry::aabb::Aabb;
+
+use crate::{
+    Bvh, ELEMENTS_TO_ACTIVATE_LEAF, VOLUME_TO_ACTIVATE_LEAF, node::BvhNode, sort_by_largest_axis,
+    utils, utils::GetAabb,
+};
+
+/// Used to find the start addresses of the elements and nodes arrays
+#[derive(Debug)]
+pub struct StartAddresses<T> {
+    /// Base pointer to the start of the elements array
+    pub start_elements_ptr: *const T,
+    pub start_nodes_ptr: *const BvhNode,
+}
+
+impl<T> StartAddresses<T> {
+    const fn element_start_index(&self, slice: &[T]) -> isize {
+        unsafe { slice.as_ptr().offset_from(self.start_elements_ptr) }
+    }
+
+    const fn node_start_index(&self, slice: &[BvhNode]) -> isize {
+        unsafe { slice.as_ptr().offset_from(self.start_nodes_ptr) }
+    }
+}
+
+unsafe impl<T: Send> Send for StartAddresses<T> {}
+unsafe impl<T: Sync> Sync for StartAddresses<T> {}
+
+impl<T> Bvh<T>
+where
+    T: Debug + Send + Copy + Sync,
+{
+    #[tracing::instrument(skip_all, fields(elements_len = elements.len()))]
+    pub fn build(mut elements: Vec<T>, get_aabb: (impl GetAabb<T> + Sync)) -> Self {
+        let max_threads = utils::thread_count_pow2();
+
+        let len = elements.len();
+
+        // // 1.7 works too, 2.0 is upper bound ... 1.8 is probably best
+        // todo: make this more mathematically derived
+        let capacity = ((len / ELEMENTS_TO_ACTIVATE_LEAF) as f64 * 8.0) as usize;
+
+        // [A]
+        let capacity = capacity.max(16);
+
+        let mut nodes = vec![BvhNode::DUMMY; capacity];
+
+        let bvh = StartAddresses {
+            start_elements_ptr: elements.as_ptr(),
+            start_nodes_ptr: nodes.as_ptr(),
+        };
+
+        #[expect(
+            clippy::indexing_slicing,
+            reason = "Look at [A]. The length is at least 16, so this is safe."
+        )]
+        let nodes_slice = &mut nodes[1..];
+
+        let (root, _) = build_in(&bvh, &mut elements, max_threads, 0, nodes_slice, &get_aabb);
+
+        Self {
+            nodes,
+            elements,
+            root,
+        }
+    }
+}
+
+#[allow(clippy::float_cmp)]
+pub fn build_in<T>(
+    addresses: &StartAddresses<T>,
+    elements: &mut [T],
+    max_threads: usize,
+    nodes_idx: usize,
+    nodes: &mut [BvhNode],
+    get_aabb: &(impl GetAabb<T> + Sync),
+) -> (i32, usize)
+where
+    T: Send + Copy + Sync + Debug,
+{
+    // aabb that encompasses all elements
+    let aabb: Aabb = elements.iter().map(get_aabb).collect();
+    let volume = aabb.volume();
+
+    if elements.len() <= ELEMENTS_TO_ACTIVATE_LEAF || volume <= VOLUME_TO_ACTIVATE_LEAF {
+        let idx_start = addresses.element_start_index(elements);
+
+        let node = BvhNode::create_leaf(aabb, idx_start as usize, elements.len());
+
+        let set = &mut nodes[nodes_idx..=nodes_idx];
+        set[0] = node;
+
+        let idx = addresses.node_start_index(set);
+
+        let idx = idx as i32;
+
+        debug_assert!(idx > 0);
+
+        return (idx, nodes_idx + 1);
+    }
+
+    sort_by_largest_axis(elements, &aabb, get_aabb);
+
+    let element_split_idx = elements.len() / 2;
+
+    let (left_elems, right_elems) = elements.split_at_mut(element_split_idx);
+
+    debug_assert!(max_threads != 0);
+
+    let original_node_idx = nodes_idx;
+
+    let (left, right, nodes_idx, to_set) = if max_threads == 1 {
+        let start_idx = nodes_idx;
+        let (left, nodes_idx) = build_in(
+            addresses,
+            left_elems,
+            max_threads,
+            nodes_idx + 1,
+            nodes,
+            get_aabb,
+        );
+
+        let (right, nodes_idx) = build_in(
+            addresses,
+            right_elems,
+            max_threads,
+            nodes_idx,
+            nodes,
+            get_aabb,
+        );
+        let end_idx = nodes_idx;
+
+        debug_assert!(start_idx != end_idx);
+
+        (
+            left,
+            right,
+            nodes_idx,
+            &mut nodes[original_node_idx..=original_node_idx],
+        )
+    } else {
+        let max_threads = max_threads >> 1;
+
+        let (to_set, nodes) = nodes.split_at_mut(1);
+
+        let node_split_idx = nodes.len() / 2;
+        let (left_nodes, right_nodes) = match true {
+            true => {
+                let (left, right) = nodes.split_at_mut(node_split_idx);
+                (left, right)
+            }
+            false => {
+                let (right, left) = nodes.split_at_mut(node_split_idx);
+                (left, right)
+            }
+        };
+
+        let (left, right) = rayon::join(
+            || build_in(addresses, left_elems, max_threads, 0, left_nodes, get_aabb),
+            || {
+                build_in(
+                    addresses,
+                    right_elems,
+                    max_threads,
+                    0,
+                    right_nodes,
+                    get_aabb,
+                )
+            },
+        );
+
+        (left.0, right.0, 0, to_set)
+    };
+
+    let node = BvhNode { aabb, left, right };
+
+    to_set[0] = node;
+    let idx = unsafe { to_set.as_ptr().offset_from(addresses.start_nodes_ptr) };
+    let idx = idx as i32;
+
+    // trace!("internal nodes_idx {:03}", original_node_idx);
+
+    debug_assert!(idx > 0);
+
+    (idx, nodes_idx + 1)
+}