Split the broad-phase code into multiple files.

src/geometry/broad_phase_multi_sap/broad_phase_proxy.rs

@@ -0,0 +1,68 @@
+use super::NEXT_FREE_SENTINEL;
+use crate::geometry::ColliderHandle;
+use parry::bounding_volume::AABB;
+use std::ops::{Index, IndexMut};
+
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Clone)]
+pub(crate) struct BroadPhaseProxy {
+    pub handle: ColliderHandle,
+    pub aabb: AABB,
+    pub next_free: u32,
+}
+
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Clone)]
+pub(crate) struct BroadPhaseProxies {
+    pub elements: Vec<BroadPhaseProxy>,
+    pub first_free: u32,
+}
+
+impl BroadPhaseProxies {
+    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 BroadPhaseProxies {
+    type Output = BroadPhaseProxy;
+    fn index(&self, i: usize) -> &BroadPhaseProxy {
+        self.elements.index(i)
+    }
+}
+
+impl IndexMut<usize> for BroadPhaseProxies {
+    fn index_mut(&mut self, i: usize) -> &mut BroadPhaseProxy {
+        self.elements.index_mut(i)
+    }
+}