From 05135beb87bbf0edace544b80ba40e327d9a89ac Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Sat, 15 Aug 2026 20:44:10 -0700
Subject: factor code out of main, optimizations

---
 src/sim/sim.rs   | 14 ++++++++++----
 src/sim/world.rs |  8 ++++----
 2 files changed, 14 insertions(+), 8 deletions(-)

(limited to 'src/sim')

diff --git a/src/sim/sim.rs b/src/sim/sim.rs
index ef2fc80..4c6d908 100644
--- a/src/sim/sim.rs
+++ b/src/sim/sim.rs
@@ -1,5 +1,6 @@
-use std::{collections::HashMap, marker::PhantomData};
+use std::marker::PhantomData;
 
+use fxhash::FxHashMap;
 use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
 
 use crate::{
@@ -73,11 +74,13 @@ pub fn set_cell(chunks: &mut [Option<&mut Chunk>; 9], x: i32, y: i32, cell: Cell
         if let Some(chunk) = &mut chunks[(dcx + 1 + (dcy + 1) * 3) as usize] {
             chunk.set_cell_at_local_position(nc_x, nc_y, cell);
             chunk.needs_texture_update = true;
+            chunk.sleeping = false;
         }
     } else {
         if let Some(target) = &mut chunks[4] {
             target.set_cell_at_local_position(x as u8, y as u8, cell);
             target.needs_texture_update = true;
+            target.sleeping = false;
         }
     }
 }
@@ -90,15 +93,18 @@ impl UpdateCtx<'_, '_, '_> {
     }
 
     fn set_cell(&mut self, dx: i32, dy: i32, cell: Cell) {
+        // cannot move out of the neighbourhood, but also cannot move to the edge of the neighbourhood
+        // as this would wake a chunk outside of the neighbourhood
+        debug_assert!(dx > -15 && dx < 15);
+        debug_assert!(dy > -15 && dy < 15);
         let x = self.x + dx;
         let y = self.y + dy;
         set_cell(self.chunks, x, y, cell);
-        // wake all the chunks
         self.chunks.iter_mut().for_each(|c| {
             if let Some(chunk) = c {
                 chunk.sleeping = false;
             }
-        });
+        })
     }
 
     pub fn candidates_swap(&mut self, candidates: &[(i32, i32)]) -> bool {
@@ -170,7 +176,7 @@ const NEIGHBORHOOD_OFFSETS: [(i32, i32); 9] = [
 pub fn sim_tick(world: &mut World, seqno: u64, use_threading: bool) {
     puffin::profile_function!();
 
-    let mut columns: HashMap<i32, Vec<i32>> = HashMap::new();
+    let mut columns: FxHashMap<i32, Vec<i32>> = FxHashMap::default();
     for &(cx, cy) in world.chunk_position_to_chunk_idx.keys() {
         columns.entry(cx).or_default().push(cy);
     }
diff --git a/src/sim/world.rs b/src/sim/world.rs
index bdb1286..6645d4e 100644
--- a/src/sim/world.rs
+++ b/src/sim/world.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use fxhash::FxHashMap;
 
 use crate::{
     config::CHUNK_SIZE,
@@ -7,8 +7,8 @@ use crate::{
 
 pub struct World {
     pub chunks: Vec<Chunk>,
-    // TODO FxHashMap?
-    pub chunk_position_to_chunk_idx: HashMap<(i32, i32), usize>,
+    // TODO FxFxHashMap?
+    pub chunk_position_to_chunk_idx: FxHashMap<(i32, i32), usize>,
 }
 
 impl World {
@@ -60,7 +60,7 @@ impl World {
     pub fn from_default_size() -> Self {
         let mut world = World {
             chunks: Vec::new(),
-            chunk_position_to_chunk_idx: HashMap::new(),
+            chunk_position_to_chunk_idx: FxHashMap::default(),
         };
 
         for y in -10..10 {
-- 
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