1 files changed, 53 insertions, 5 deletions

diff --git a/src/sim/sim_manager/utils.rs b/src/sim/sim_manager/utils.rs
index f30e9a0..264597d 100644
--- a/src/sim/sim_manager/utils.rs
+++ b/src/sim/sim_manager/utils.rs
@@ -1,10 +1,13 @@
 use glam::IVec2;
+use rapier2d::{dynamics::RigidBodyBuilder, math::Pose};
 
 use crate::{
+    config::CELLS_TO_METRES,
     content::materials::MaterialId,
     sim::{
         cell::Cell,
-        entity::{EntityId, EntityUpdateResult},
+        entity::{EntityCells, EntityDef, EntityId, EntityUpdateResult},
+        lib::components::compute_components,
         sim_manager::SimManager,
     },
 };
@@ -117,10 +120,17 @@ pub fn read_back_entities_from_world(
         if let Some(entity) = &mut entity
             && should_update_entity
         {
-            puffin::profile_scope!("Recompute collider");
-            if let Some(new_collider) = entity.compute_collider() {
-                {
-                    puffin::profile_scope!("Upsert collider");
+            // correctness: there's no way to get here if the entity is an uncelled entity
+            let ec = entity.data.cells.as_mut().unwrap();
+            // first check if the entity has been partitioned
+            let components = compute_components(&ec.cells, ec.size.x, ec.size.y);
+            if components.len() == 0 {
+                panic!("The entity was completely destroyed?")
+            } else if components.len() == 1 {
+                // the entity's cells were changed, but not partitioned
+                puffin::profile_scope!("Recompute collider");
+                if let Some(new_collider) = entity.compute_collider() {
+                    // don't profile this separately as it's basically free
                     sim.rb_manager
                         .physics_manager
                         .world
@@ -134,6 +144,44 @@ pub fn read_back_entities_from_world(
 
                     entity.data.collider_h = Some(new_handle);
                 }
+            } else {
+                // the entity was partitioned
+                // destroy the original entity
+                // correctness -- not correct! because we don't have pos without rb
+                let old_rb = sim
+                    .rb_manager
+                    .physics_manager
+                    .world
+                    .bodies
+                    .get(entity.data.rb_h.unwrap())
+                    .unwrap();
+                let old_pose = old_rb.position().clone();
+                let old_linvel = old_rb.linvel().clone();
+                let old_angvel = old_rb.angvel().clone();
+
+                sim.destroy_entity(entity_id);
+                // and create a new entity for each component
+                for component in components {
+                    let r = old_pose.transform_vector(component.position / CELLS_TO_METRES);
+                    let mut pose = old_pose;
+                    pose.translation += r;
+
+                    let rb = RigidBodyBuilder::dynamic()
+                        .pose(pose)
+                        .linvel(old_linvel)
+                        .angvel(old_angvel)
+                        .build();
+
+                    let def = EntityDef::from_cells_and_rb(
+                        EntityCells {
+                            cells: component.cells,
+                            size: component.size,
+                        },
+                        rb,
+                        None,
+                    );
+                    sim.create_entity(def);
+                }
             }
         }
     }