Split the broad-phase code into multiple files.

9 files changed, 836 insertions, 794 deletions

diff --git a/src/geometry/broad_phase_multi_sap.rs b/src/geometry/broad_phase_multi_sap.rs
deleted file mode 100644
index 1b780c3..0000000
--- a/src/geometry/broad_phase_multi_sap.rs
+++ /dev/null
@@ -1,794 +0,0 @@
-use crate::data::pubsub::Subscription;
-use crate::dynamics::RigidBodySet;
-use crate::geometry::{ColliderHandle, ColliderSet, RemovedCollider};
-use crate::math::{Point, Real, Vector, DIM};
-use bit_vec::BitVec;
-use parry::bounding_volume::{BoundingVolume, AABB};
-use parry::utils::hashmap::HashMap;
-use std::cmp::Ordering;
-use std::ops::{Index, IndexMut};
-
-const NUM_SENTINELS: usize = 1;
-const NEXT_FREE_SENTINEL: u32 = u32::MAX;
-const SENTINEL_VALUE: Real = Real::MAX;
-const CELL_WIDTH: Real = 20.0;
-
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
-#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-pub struct ColliderPair {
-    pub collider1: ColliderHandle,
-    pub collider2: ColliderHandle,
-}
-
-impl ColliderPair {
-    pub fn new(collider1: ColliderHandle, collider2: ColliderHandle) -> Self {
-        ColliderPair {
-            collider1,
-            collider2,
-        }
-    }
-
-    pub fn new_sorted(collider1: ColliderHandle, collider2: ColliderHandle) -> Self {
-        if collider1.into_raw_parts().0 <= collider2.into_raw_parts().0 {
-            Self::new(collider1, collider2)
-        } else {
-            Self::new(collider2, collider1)
-        }
-    }
-
-    pub fn swap(self) -> Self {
-        Self::new(self.collider2, self.collider1)
-    }
-
-    pub fn zero() -> Self {
-        Self {
-            collider1: ColliderHandle::from_raw_parts(0, 0),
-            collider2: ColliderHandle::from_raw_parts(0, 0),
-        }
-    }
-}
-
-pub enum BroadPhasePairEvent {
-    AddPair(ColliderPair),
-    DeletePair(ColliderPair),
-}
-
-fn sort2(a: u32, b: u32) -> (u32, u32) {
-    assert_ne!(a, b);
-
-    if a < b {
-        (a, b)
-    } else {
-        (b, a)
-    }
-}
-
-fn point_key(point: Point<Real>) -> Point<i32> {
-    (point / CELL_WIDTH).coords.map(|e| e.floor() as i32).into()
-}
-
-fn region_aabb(index: Point<i32>) -> AABB {
-    let mins = index.coords.map(|i| i as Real * CELL_WIDTH).into();
-    let maxs = mins + Vector::repeat(CELL_WIDTH);
-    AABB::new(mins, maxs)
-}
-
-#[derive(Copy, Clone, Debug, PartialEq)]
-#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-struct Endpoint {
-    value: Real,
-    packed_flag_proxy: u32,
-}
-
-const START_FLAG_MASK: u32 = 0b1 << 31;
-const PROXY_MASK: u32 = u32::MAX ^ START_FLAG_MASK;
-const START_SENTINEL_TAG: u32 = u32::MAX;
-const END_SENTINEL_TAG: u32 = u32::MAX ^ START_FLAG_MASK;
-
-impl Endpoint {
-    pub fn start_endpoint(value: Real, proxy: u32) -> Self {
-        Self {
-            value,
-            packed_flag_proxy: proxy | START_FLAG_MASK,
-        }
-    }
-
-    pub fn end_endpoint(value: Real, proxy: u32) -> Self {
-        Self {
-            value,
-            packed_flag_proxy: proxy & PROXY_MASK,
-        }
-    }
-
-    pub fn start_sentinel() -> Self {
-        Self {
-            value: -SENTINEL_VALUE,
-            packed_flag_proxy: START_SENTINEL_TAG,
-        }
-    }
-
-    pub fn end_sentinel() -> Self {
-        Self {
-            value: SENTINEL_VALUE,
-            packed_flag_proxy: END_SENTINEL_TAG,
-        }
-    }
-
-    pub fn is_sentinel(self) -> bool {
-        self.packed_flag_proxy & PROXY_MASK == PROXY_MASK
-    }
-
-    pub fn proxy(self) -> u32 {
-        self.packed_flag_proxy & PROXY_MASK
-    }
-
-    pub fn is_start(self) -> bool {
-        (self.packed_flag_proxy & START_FLAG_MASK) != 0
-    }
-
-    pub fn is_end(self) -> bool {
-        (self.packed_flag_proxy & START_FLAG_MASK) == 0
-    }
-}
-
-#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-#[derive(Clone)]
-struct SAPAxis {
-    min_bound: Real,
-    max_bound: Real,
-    endpoints: Vec<Endpoint>,
-    #[cfg_attr(feature = "serde-serialize", serde(skip))]
-    new_endpoints: Vec<(Endpoint, usize)>, // Workspace
-}
-
-impl SAPAxis {
-    fn new(min_bound: Real, max_bound: Real) -> Self {
-        assert!(min_bound <= max_bound);
-
-        Self {
-            min_bound,
-            max_bound,
-            endpoints: vec![Endpoint::start_sentinel(), Endpoint::end_sentinel()],
-            new_endpoints: Vec::new(),
-        }
-    }
-
-    fn batch_insert(
-        &mut self,
-        dim: usize,
-        new_proxies: &[usize],
-        proxies: &Proxies,
-        reporting: Option<&mut HashMap<(u32, u32), bool>>,
-    ) {
-        if new_proxies.is_empty() {
-            return;
-        }
-
-        self.new_endpoints.clear();
-
-        for proxy_id in new_proxies {
-            let proxy = &proxies[*proxy_id];
-            assert!(proxy.aabb.mins[dim] <= self.max_bound);
-            assert!(proxy.aabb.maxs[dim] >= self.min_bound);
-            let start_endpoint = Endpoint::start_endpoint(proxy.aabb.mins[dim], *proxy_id as u32);
-            let end_endpoint = Endpoint::end_endpoint(proxy.aabb.maxs[dim], *proxy_id as u32);
-
-            self.new_endpoints.push((start_endpoint, 0));
-            self.new_endpoints.push((end_endpoint, 0));
-        }
-
-        self.new_endpoints
-            .sort_by(|a, b| a.0.value.partial_cmp(&b.0.value).unwrap_or(Ordering::Equal));
-
-        let mut curr_existing_index = self.endpoints.len() - NUM_SENTINELS - 1;
-        let new_num_endpoints = self.endpoints.len() + self.new_endpoints.len();
-        self.endpoints
-            .resize(new_num_endpoints, Endpoint::end_sentinel());
-        let mut curr_shift_index = new_num_endpoints - NUM_SENTINELS - 1;
-
-        // Sort the endpoints.
-        // TODO: specialize for the case where this is the
-        // first time we insert endpoints to this axis?
-        for new_endpoint in self.new_endpoints.iter_mut().rev() {
-            loop {
-                let existing_endpoint = self.endpoints[curr_existing_index];
-                if existing_endpoint.value <= new_endpoint.0.value {
-                    break;
-                }
-
-                self.endpoints[curr_shift_index] = existing_endpoint;
-
-                curr_shift_index -= 1;
-                curr_existing_index -= 1;
-            }
-
-            self.endpoints[curr_shift_index] = new_endpoint.0;
-            new_endpoint.1 = curr_shift_index;
-            curr_shift_index -= 1;
-        }
-
-        // Report pairs using a single mbp pass on each new endpoint.
-        let endpoints_wo_last_sentinel = &self.endpoints[..self.endpoints.len() - 1];
-        if let Some(reporting) = reporting {
-            for (endpoint, endpoint_id) in self.new_endpoints.drain(..).filter(|e| e.0.is_start()) {
-                let proxy1 = &proxies[endpoint.proxy() as usize];
-                let min = endpoint.value;
-                let max = proxy1.aabb.maxs[dim];
-
-                for endpoint2 in &endpoints_wo_last_sentinel[endpoint_id + 1..] {
-                    if endpoint2.proxy() == endpoint.proxy() {
-                        continue;
-                    }
-
-                    let proxy2 = &proxies[endpoint2.proxy() as usize];
-
-                    // NOTE: some pairs with equal aabb.mins[dim] may end up being reported twice.
-                    if (endpoint2.is_start() && endpoint2.value < max)
-                        || (endpoint2.is_end() && proxy2.aabb.mins[dim] <= min)
-                    {
-                        // Report pair.
-                        if proxy1.aabb.intersects(&proxy2.aabb) {
-                            // Report pair.
-                            let pair = sort2(endpoint.proxy(), endpoint2.proxy());
-                            reporting.insert(pair, true);
-                        }
-                    }
-                }
-            }
-        }
-    }
-
-    fn delete_out_of_bounds_proxies(&self, existing_proxies: &mut BitVec) -> usize {
-        let mut deleted = 0;
-        for endpoint in &self.endpoints {
-            if endpoint.value < self.min_bound {
-                let proxy_idx = endpoint.proxy() as usize;
-                if endpoint.is_end() && existing_proxies[proxy_idx] {
-                    existing_proxies.set(proxy_idx, false);
-                    deleted += 1;
-                }
-            } else {
-                break;
-            }
-        }
-
-        for endpoint in self.endpoints.iter().rev() {
-            if endpoint.value > self.max_bound {
-                let proxy_idx = endpoint.proxy() as usize;
-                if endpoint.is_start() && existing_proxies[proxy_idx] {
-                    existing_proxies.set(endpoint.proxy() as usize, false);
-                    deleted += 1;
-                }
-            } else {
-                break;
-            }
-        }
-
-        deleted
-    }
-
-    fn delete_out_of_bounds_endpoints(&mut self, existing_proxies: &BitVec) {
-        self.endpoints
-            .retain(|endpt| endpt.is_sentinel() || existing_proxies[endpt.proxy() as usize])
-    }
-
-    fn update_endpoints(
-        &mut self,
-        dim: usize,
-        proxies: &Proxies,
-        reporting: &mut HashMap<(u32, u32), bool>,
-    ) {
-        let last_endpoint = self.endpoints.len() - NUM_SENTINELS;
-        for i in NUM_SENTINELS..last_endpoint {
-            let mut endpoint_i = self.endpoints[i];
-            let aabb_i = proxies[endpoint_i.proxy() as usize].aabb;
-
-            if endpoint_i.is_start() {
-                endpoint_i.value = aabb_i.mins[dim];
-            } else {
-                endpoint_i.value = aabb_i.maxs[dim];
-            }
-
-            let mut j = i;
-
-            if endpoint_i.is_start() {
-                while endpoint_i.value < self.endpoints[j - 1].value {
-                    let endpoint_j = self.endpoints[j - 1];
-                    self.endpoints[j] = endpoint_j;
-
-                    if endpoint_j.is_end() {
-                        // Report start collision.
-                        if aabb_i.intersects(&proxies[endpoint_j.proxy() as usize].aabb) {
-                            let pair = sort2(endpoint_i.proxy(), endpoint_j.proxy());
-                            reporting.insert(pair, true);
-                        }
-                    }
-
-                    j -= 1;
-                }
-            } else {
-                while endpoint_i.value < self.endpoints[j - 1].value {
-                    let endpoint_j = self.endpoints[j - 1];
-                    self.endpoints[j] = endpoint_j;
-
-                    if endpoint_j.is_start() {
-                        // Report end collision.
-                        if !aabb_i.intersects(&proxies[endpoint_j.proxy() as usize].aabb) {
-                            let pair = sort2(endpoint_i.proxy(), endpoint_j.proxy());
-                            reporting.insert(pair, false);
-                        }
-                    }
-
-                    j -= 1;
-                }
-            }
-
-            self.endpoints[j] = endpoint_i;
-        }
-
-        // println!(
-        //     "Num start swaps: {}, end swaps: {}, dim: {}",
-        //     num_start_swaps, num_end_swaps, dim
-        // );
-    }
-}
-
-#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-#[derive(Clone)]
-struct SAPRegion {
-    axes: [SAPAxis; DIM],
-    existing_proxies: BitVec,
-    #[cfg_attr(feature = "serde-serialize", serde(skip))]
-    to_insert: Vec<usize>, // Workspace
-    update_count: u8,
-    proxy_count: usize,
-}
-
-impl SAPRegion {
-    pub fn new(bounds: AABB) -> Self {
-        let axes = [
-            SAPAxis::new(bounds.mins.x, bounds.maxs.x),
-            SAPAxis::new(bounds.mins.y, bounds.maxs.y),
-            #[cfg(feature = "dim3")]
-            SAPAxis::new(bounds.mins.z, bounds.maxs.z),
-        ];
-        SAPRegion {
-            axes,
-            existing_proxies: BitVec::new(),
-            to_insert: Vec::new(),
-            update_count: 0,
-            proxy_count: 0,
-        }
-    }
-
-    pub fn recycle(bounds: AABB, mut old: Self) -> Self {
-        // Correct the bounds
-        for (axis, &bound) in old.axes.iter_mut().zip(bounds.mins.iter()) {
-            axis.min_bound = bound;
-        }
-        for (axis, &bound) in old.axes.iter_mut().zip(bounds.maxs.iter()) {
-            axis.max_bound = bound;
-        }
-
-        old.update_count = 0;
-
-        // The rest of the fields should be "empty"
-        assert_eq!(old.proxy_count, 0);
-        assert!(old.to_insert.is_empty());
-        debug_assert!(!old.existing_proxies.any());
-        assert!(old.axes.iter().all(|ax| ax.endpoints.len() == 2));
-
-        old
-    }
-
-    pub fn recycle_or_new(bounds: AABB, pool: &mut Vec<Self>) -> Self {
-        if let Some(old) = pool.pop() {
-            Self::recycle(bounds, old)
-        } else {
-            Self::new(bounds)
-        }
-    }
-
-    pub fn predelete_proxy(&mut self, _proxy_id: usize) {
-        // We keep the proxy_id as argument for uniformity with the "preupdate"
-        // method. However we don't actually need it because the deletion will be
-        // handled transparently during the next update.
-        self.update_count = 1;
-    }
-
-    pub fn preupdate_proxy(&mut self, proxy_id: usize) -> bool {
-        let mask_len = self.existing_proxies.len();
-        if proxy_id >= mask_len {
-            self.existing_proxies.grow(proxy_id + 1 - mask_len, false);
-        }
-
-        if !self.existing_proxies[proxy_id] {
-            self.to_insert.push(proxy_id);
-            self.existing_proxies.set(proxy_id, true);
-            self.proxy_count += 1;
-            false
-        } else {
-            // Here we need a second update if all proxies exit this region. In this case, we need
-            // to delete the final proxy, but the region may not have AABBs overlapping it, so it
-            // wouldn't get an update otherwise.
-            self.update_count = 2;
-            true
-        }
-    }
-
-    pub fn update(&mut self, proxies: &Proxies, reporting: &mut HashMap<(u32, u32), bool>) {
-        if self.update_count > 0 {
-            // Update endpoints.
-            let mut deleted = 0;
-
-            for dim in 0..DIM {
-                self.axes[dim].update_endpoints(dim, proxies, reporting);
-                deleted += self.axes[dim].delete_out_of_bounds_proxies(&mut self.existing_proxies);
-            }
-
-            if deleted > 0 {
-                self.proxy_count -= deleted;
-                for dim in 0..DIM {
-                    self.axes[dim].delete_out_of_bounds_endpoints(&self.existing_proxies);
-                }
-            }
-
-            self.update_count -= 1;
-        }
-
-        if !self.to_insert.is_empty() {
-            // Insert new proxies.
-            for dim in 1..DIM {
-                self.axes[dim].batch_insert(dim, &self.to_insert, proxies, None);
-            }
-            self.axes[0].batch_insert(0, &self.to_insert, proxies, Some(reporting));
-            self.to_insert.clear();
-
-            // In the rare event that all proxies leave this region in the next step, we need an
-            // update to remove them.
-            self.update_count = 1;
-        }
-    }
-}
-
-/// A broad-phase based on multiple Sweep-and-Prune instances running of disjoint region of the 3D world.
-#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-#[derive(Clone)]
-pub struct BroadPhase {
-    proxies: Proxies,
-    regions: HashMap<Point<i32>, SAPRegion>,
-    removed_colliders: Option<Subscription<RemovedCollider>>,
-    deleted_any: bool,
-    #[cfg_attr(feature = "serde-serialize", serde(skip))]
-    region_pool: Vec<SAPRegion>, // To avoid repeated allocations.
-    #[cfg_attr(feature = "serde-serialize", serde(skip))]
-    regions_to_remove: Vec<Point<i32>>, // Workspace
-    // We could think serializing this workspace is useless.
-    // It turns out is is important to serialize at least its capacity
-    // and restore this capacity when deserializing the hashmap.
-    // This is because the order of future elements inserted into the
-    // hashmap depends on its capacity (because the internal bucket indices
-    // depend on this capacity). So not restoring this capacity may alter
-    // the order at which future elements are reported. This will in turn
-    // alter the order at which the pairs are registered in the narrow-phase,
-    // thus altering the order of the contact manifold. In the end, this
-    // alters the order of the resolution of contacts, resulting in
-    // diverging simulation after restoration of a snapshot.
-    #[cfg_attr(
-        feature = "serde-serialize",
-        serde(
-            serialize_with = "parry::utils::hashmap::serialize_hashmap_capacity",
-            deserialize_with = "parry::utils::hashmap::deserialize_hashmap_capacity"
-        )
-    )]
-    reporting: HashMap<(u32, u32), bool>, // Workspace
-}
-
-#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-#[derive(Clone)]
-pub(crate) struct BroadPhaseProxy {
-    handle: ColliderHandle,
-    aabb: AABB,
-    next_free: u32,
-}
-
-#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-#[derive(Clone)]
-struct Proxies {
-    elements: Vec<BroadPhaseProxy>,
-    first_free: u32,
-}
-
-impl Proxies {
-    pub fn new() -> Self {
-        Self {
-            elements: Vec::new(),
-            first_free: NEXT_FREE_SENTINEL,
-        }
-    }
-
-    pub fn insert(&mut self, proxy: BroadPhaseProxy) -> usize {
-        if self.first_free != NEXT_FREE_SENTINEL {
-            let proxy_id = self.first_free as usize;
-            self.first_free = self.elements[proxy_id].next_free;
-            self.elements[proxy_id] = proxy;
-            proxy_id
-        } else {
-            self.elements.push(proxy);
-            self.elements.len() - 1
-        }
-    }
-
-    pub fn remove(&mut self, proxy_id: usize) {
-        self.elements[proxy_id].next_free = self.first_free;
-        self.first_free = proxy_id as u32;
-    }
-
-    // // FIXME: take holes into account?
-    // pub fn get(&self, i: usize) -> Option<&BroadPhaseProxy> {
-    //     self.elements.get(i)
-    // }
-
-    // FIXME: take holes into account?
-    pub fn get_mut(&mut self, i: usize) -> Option<&mut BroadPhaseProxy> {
-        self.elements.get_mut(i)
-    }
-}
-
-impl Index<usize> for Proxies {
-    type Output = BroadPhaseProxy;
-    fn index(&self, i: usize) -> &BroadPhaseProxy {
-        self.elements.index(i)
-    }
-}
-
-impl IndexMut<usize> for Proxies {
-    fn index_mut(&mut self, i: usize) -> &mut BroadPhaseProxy {
-        self.elements.index_mut(i)
-    }
-}
-
-impl BroadPhase {
-    /// Create a new empty broad-phase.
-    pub fn new() -> Self {
-        BroadPhase {
-            removed_colliders: None,
-            proxies: Proxies::new(),
-            regions: HashMap::default(),
-            region_pool: Vec::new(),
-            regions_to_remove: Vec::new(),
-            reporting: HashMap::default(),
-            deleted_any: false,
-        }
-    }
-
-    /// Maintain the broad-phase internal state by taking collider removal into account.
-    pub fn maintain(&mut self, colliders: &mut ColliderSet) {
-        // Ensure we already subscribed.
-        if self.removed_colliders.is_none() {
-            self.removed_colliders = Some(colliders.removed_colliders.subscribe());
-        }
-
-        let cursor = self.removed_colliders.take().unwrap();
-        for collider in colliders.removed_colliders.read(&cursor) {
-            self.remove_collider(collider.proxy_index);
-        }
-
-        colliders.removed_colliders.ack(&cursor);
-        self.removed_colliders = Some(cursor);
-    }
-
-    fn remove_collider(&mut self, proxy_index: usize) {
-        if proxy_index == crate::INVALID_USIZE {
-            // This collider has not been added to the broad-phase yet.
-            return;
-        }
-
-        let proxy = &mut self.proxies[proxy_index];
-
-        // Discretize the AABB to find the regions that need to be invalidated.
-        let start = point_key(proxy.aabb.mins);
-        let end = point_key(proxy.aabb.maxs);
-
-        #[cfg(feature = "dim2")]
-        for i in start.x..=end.x {
-            for j in start.y..=end.y {
-                if let Some(region) = self.regions.get_mut(&Point::new(i, j)) {
-                    region.predelete_proxy(proxy_index);
-                    self.deleted_any = true;
-                }
-            }
-        }
-
-        #[cfg(feature = "dim3")]
-        for i in start.x..=end.x {
-            for j in start.y..=end.y {
-                for k in start.z..=end.z {
-                    if let Some(region) = self.regions.get_mut(&Point::new(i, j, k)) {
-                        region.predelete_proxy(proxy_index);
-                        self.deleted_any = true;
-                    }
-                }
-            }
-        }
-
-        // Push the proxy to infinity, but not beyond the sentinels.
-        proxy.aabb.mins.coords.fill(SENTINEL_VALUE / 2.0);
-        proxy.aabb.maxs.coords.fill(SENTINEL_VALUE / 2.0);
-        self.proxies.remove(proxy_index);
-    }
-
-    pub(crate) fn update_aabbs(
-        &mut self,
-        prediction_distance: Real,
-        bodies: &RigidBodySet,
-        colliders: &mut ColliderSet,
-    ) {
-        // First, if we have any pending removals we have
-        // to deal with them now because otherwise we will
-        // end up with an ABA problems when reusing proxy
-        // ids.
-        self.complete_removals();
-
-        for body_handle in bodies
-            .modified_inactive_set
-            .iter()
-            .chain(bodies.active_dynamic_set.iter())
-            .chain(bodies.active_kinematic_set.iter())
-        {
-            for handle in &bodies[*body_handle].colliders {
-                let collider = &mut colliders[*handle];
-                let aabb = collider.compute_aabb().loosened(prediction_distance / 2.0);
-
-                if let Some(proxy) = self.proxies.get_mut(collider.proxy_index) {
-                    proxy.aabb = aabb;
-                } else {
-                    let proxy = BroadPhaseProxy {
-                        handle: *handle,
-                        aabb,
-                        next_free: NEXT_FREE_SENTINEL,
-                    };
-                    collider.proxy_index = self.proxies.insert(proxy);
-                }
-
-                // Discretize the aabb.
-                let proxy_id = collider.proxy_index;
-                // let start = Point::origin();
-                // let end = Point::origin();
-                let start = point_key(aabb.mins);
-                let end = point_key(aabb.maxs);
-
-                let regions = &mut self.regions;
-                let pool = &mut self.region_pool;
-
-                #[cfg(feature = "dim2")]
-                for i in start.x..=end.x {
-                    for j in start.y..=end.y {
-                        let region_key = Point::new(i, j);
-                        let region_bounds = region_aabb(region_key);
-                        let region = regions
-                            .entry(region_key)
-                            .or_insert_with(|| SAPRegion::recycle_or_new(region_bounds, pool));
-                        let _ = region.preupdate_proxy(proxy_id);
-                    }
-                }
-
-                #[cfg(feature = "dim3")]
-                for i in start.x..=end.x {
-                    for j in start.y..=end.y {
-                        for k in start.z..=end.z {
-                            let region_key = Point::new(i, j, k);
-                            let region_bounds = region_aabb(region_key);
-                            let region = regions
-                                .entry(region_key)
-                                .or_insert_with(|| SAPRegion::recycle_or_new(region_bounds, pool));
-                            let _ = region.preupdate_proxy(proxy_id);
-                        }
-                    }
-                }
-            }
-        }
-    }
-
-    fn update_regions(&mut self) {
-        for (point, region) in &mut self.regions {
-            region.update(&self.proxies, &mut self.reporting);
-            if region.proxy_count == 0 {
-                self.regions_to_remove.push(*point);
-            }
-        }
-
-        // Remove all the empty regions and store them in the region pool
-        let regions = &mut self.regions;
-        self.region_pool.extend(
-            self.regions_to_remove
-                .drain(..)
-                .map(|p| regions.remove(&p).unwrap()),
-        );
-    }
-
-    pub(crate) fn complete_removals(&mut self) {
-        if self.deleted_any {
-            self.update_regions();
-
-            // NOTE: we don't care about reporting pairs.
-            self.reporting.clear();
-            self.deleted_any = false;
-        }
-    }
-
-    pub(crate) fn find_pairs(&mut self, out_events: &mut Vec<BroadPhasePairEvent>) {
-        // println!("num regions: {}", self.regions.len());
-
-        self.reporting.clear();
-        self.update_regions();
-
-        // Convert reports to broad phase events.
-        // let t = instant::now();
-        // let mut num_add_events = 0;
-        // let mut num_delete_events = 0;
-
-        for ((proxy1, proxy2), colliding) in &self.reporting {
-            let proxy1 = &self.proxies[*proxy1 as usize];
-            let proxy2 = &self.proxies[*proxy2 as usize];
-
-            let handle1 = proxy1.handle;
-            let handle2 = proxy2.handle;
-
-            if *colliding {
-                out_events.push(BroadPhasePairEvent::AddPair(ColliderPair::new(
-                    handle1, handle2,
-                )));
-            // num_add_events += 1;
-            } else {
-                out_events.push(BroadPhasePairEvent::DeletePair(ColliderPair::new(
-                    handle1, handle2,
-                )));
-                // num_delete_events += 1;
-            }
-        }
-
-        // println!(
-        //     "Event conversion time: {}, add: {}/{}, delete: {}/{}",
-        //     instant::now() - t,
-        //     num_add_events,
-        //     out_events.len(),
-        //     num_delete_events,
-        //     out_events.len()
-        // );
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use crate::dynamics::{JointSet, RigidBodyBuilder, RigidBodySet};
-    use crate::geometry::{BroadPhase, ColliderBuilder, ColliderSet};
-
-    #[test]
-    fn test_add_update_remove() {
-        let mut broad_phase = BroadPhase::new();
-        let mut bodies = RigidBodySet::new();
-        let mut colliders = ColliderSet::new();
-        let mut joints = JointSet::new();
-
-        let rb = RigidBodyBuilder::new_dynamic().build();
-        let co = ColliderBuilder::ball(0.5).build();
-        let hrb = bodies.insert(rb);
-        colliders.insert(co, hrb, &mut bodies);
-
-        broad_phase.update_aabbs(0.0, &bodies, &mut colliders);
-
-        bodies.remove(hrb, &mut colliders, &mut joints);
-        broad_phase.maintain(&mut colliders);
-        broad_phase.update_aabbs(0.0, &bodies, &mut colliders);
-
-        // Create another body.
-        let rb = RigidBodyBuilder::new_dynamic().build();
-        let co = ColliderBuilder::ball(0.5).build();
-        let hrb = bodies.insert(rb);
-        colliders.insert(co, hrb, &mut bodies);
-
-        // Make sure the proxy handles is recycled properly.
-        broad_phase.update_aabbs(0.0, &bodies, &mut colliders);
-    }
-}
diff --git a/src/geometry/broad_phase_multi_sap/broad_phase.rs b/src/geometry/broad_phase_multi_sap/broad_phase.rs
new file mode 100644
index 0000000..f7006d3
--- /dev/null
+++ b/src/geometry/broad_phase_multi_sap/broad_phase.rs
@@ -0,0 +1,288 @@
+use super::{
+    BroadPhasePairEvent, BroadPhaseProxies, BroadPhaseProxy, ColliderPair, SAPRegion,
+    NEXT_FREE_SENTINEL, SENTINEL_VALUE,
+};
+use crate::data::pubsub::Subscription;
+use crate::dynamics::RigidBodySet;
+use crate::geometry::{ColliderSet, RemovedCollider};
+use crate::math::{Point, Real};
+use parry::bounding_volume::BoundingVolume;
+use parry::utils::hashmap::HashMap;
+
+/// A broad-phase based on multiple Sweep-and-Prune instances running of disjoint region of the 3D world.
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Clone)]
+pub struct BroadPhase {
+    proxies: BroadPhaseProxies,
+    regions: HashMap<Point<i32>, SAPRegion>,
+    removed_colliders: Option<Subscription<RemovedCollider>>,
+    deleted_any: bool,
+    #[cfg_attr(feature = "serde-serialize", serde(skip))]
+    region_pool: Vec<SAPRegion>, // To avoid repeated allocations.
+    #[cfg_attr(feature = "serde-serialize", serde(skip))]
+    regions_to_remove: Vec<Point<i32>>, // Workspace
+    // We could think serializing this workspace is useless.
+    // It turns out is is important to serialize at least its capacity
+    // and restore this capacity when deserializing the hashmap.
+    // This is because the order of future elements inserted into the
+    // hashmap depends on its capacity (because the internal bucket indices
+    // depend on this capacity). So not restoring this capacity may alter
+    // the order at which future elements are reported. This will in turn
+    // alter the order at which the pairs are registered in the narrow-phase,
+    // thus altering the order of the contact manifold. In the end, this
+    // alters the order of the resolution of contacts, resulting in
+    // diverging simulation after restoration of a snapshot.
+    #[cfg_attr(
+        feature = "serde-serialize",
+        serde(
+            serialize_with = "parry::utils::hashmap::serialize_hashmap_capacity",
+            deserialize_with = "parry::utils::hashmap::deserialize_hashmap_capacity"
+        )
+    )]
+    reporting: HashMap<(u32, u32), bool>, // Workspace
+}
+
+impl BroadPhase {
+    /// Create a new empty broad-phase.
+    pub fn new() -> Self {
+        BroadPhase {
+            removed_colliders: None,
+            proxies: BroadPhaseProxies::new(),
+            regions: HashMap::default(),
+            region_pool: Vec::new(),
+            regions_to_remove: Vec::new(),
+            reporting: HashMap::default(),
+            deleted_any: false,
+        }
+    }
+
+    /// Maintain the broad-phase internal state by taking collider removal into account.
+    pub fn maintain(&mut self, colliders: &mut ColliderSet) {
+        // Ensure we already subscribed.
+        if self.removed_colliders.is_none() {
+            self.removed_colliders = Some(colliders.removed_colliders.subscribe());
+        }
+
+        let cursor = self.removed_colliders.take().unwrap();
+        for collider in colliders.removed_colliders.read(&cursor) {
+            self.remove_collider(collider.proxy_index);
+        }
+
+        colliders.removed_colliders.ack(&cursor);
+        self.removed_colliders = Some(cursor);
+    }
+
+    fn remove_collider(&mut self, proxy_index: usize) {
+        if proxy_index == crate::INVALID_USIZE {
+            // This collider has not been added to the broad-phase yet.
+            return;
+        }
+
+        let proxy = &mut self.proxies[proxy_index];
+
+        // Discretize the AABB to find the regions that need to be invalidated.
+        let start = super::point_key(proxy.aabb.mins);
+        let end = super::point_key(proxy.aabb.maxs);
+
+        #[cfg(feature = "dim2")]
+        for i in start.x..=end.x {
+            for j in start.y..=end.y {
+                if let Some(region) = self.regions.get_mut(&Point::new(i, j)) {
+                    region.predelete_proxy(proxy_index);
+                    self.deleted_any = true;
+                }
+            }
+        }
+
+        #[cfg(feature = "dim3")]
+        for i in start.x..=end.x {
+            for j in start.y..=end.y {
+                for k in start.z..=end.z {
+                    if let Some(region) = self.regions.get_mut(&Point::new(i, j, k)) {
+                        region.predelete_proxy(proxy_index);
+                        self.deleted_any = true;
+                    }
+                }
+            }
+        }
+
+        // Push the proxy to infinity, but not beyond the sentinels.
+        proxy.aabb.mins.coords.fill(SENTINEL_VALUE / 2.0);
+        proxy.aabb.maxs.coords.fill(SENTINEL_VALUE / 2.0);
+        self.proxies.remove(proxy_index);
+    }
+
+    pub(crate) fn update_aabbs(
+        &mut self,
+        prediction_distance: Real,
+        bodies: &RigidBodySet,
+        colliders: &mut ColliderSet,
+    ) {
+        // First, if we have any pending removals we have
+        // to deal with them now because otherwise we will
+        // end up with an ABA problems when reusing proxy
+        // ids.
+        self.complete_removals();
+
+        for body_handle in bodies
+            .modified_inactive_set
+            .iter()
+            .chain(bodies.active_dynamic_set.iter())