From 2640f91e36558650bb988dcc82b5148ee71f3eb0 Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Tue, 18 Aug 2026 22:22:27 -0700
Subject: optimize with settlement counter

---
 src/sim/cell_sim/sim.rs | 32 +++++++++++++++++++-------------
 1 file changed, 19 insertions(+), 13 deletions(-)

(limited to 'src/sim/cell_sim/sim.rs')

diff --git a/src/sim/cell_sim/sim.rs b/src/sim/cell_sim/sim.rs
index 8831bb4..4b9f05f 100644
--- a/src/sim/cell_sim/sim.rs
+++ b/src/sim/cell_sim/sim.rs
@@ -5,14 +5,10 @@ use rand::{Rng, SeedableRng, rngs::SmallRng};
 use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
 
 use crate::{
-    config::{CELLS_IN_CHUNK, CHUNK_SIZE},
+    config::CHUNK_SIZE,
     sim::{
-        cell::{
-            cell::Cell,
-            materials::{MaterialDef, MaterialId},
-        },
+        cell::{cell::Cell, materials::MaterialDef},
         cell_sim::{chunk::Chunk, world::World},
-        rb_sim::{RbSimManager, rb_entity::RbEntity},
     },
 };
 
@@ -87,6 +83,7 @@ pub struct UpdateCtx<'a, 'b, 'c> {
     pub material: &'c MaterialDef,
 
     pub rng: &'c mut dyn Rng,
+    swapped: bool,
 }
 
 impl UpdateCtx<'_, '_, '_> {
@@ -99,8 +96,8 @@ impl UpdateCtx<'_, '_, '_> {
     pub 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);
+        debug_assert!(dx > -CHUNK_SIZE + 1 && dx < CHUNK_SIZE - 1);
+        debug_assert!(dy > -CHUNK_SIZE + 1 && dy < CHUNK_SIZE - 1);
         let x = self.x + dx;
         let y = self.y + dy;
         set_cell(self.chunks, x, y, cell);
@@ -113,10 +110,14 @@ impl UpdateCtx<'_, '_, '_> {
 
     pub fn candidates_swap(&mut self, candidates: &[(i32, i32)]) -> bool {
         for &(dx, dy) in candidates {
-            let candidate_cell = self.get_cell(dx, dy);
-            if candidate_cell.is_some_and(|c| c.material.def().density < self.material.density) {
-                self.set_cell(0, 0, candidate_cell.unwrap());
+            if let Some(mut candidate_cell) = self.get_cell(dx, dy)
+                && candidate_cell.material.def().density < self.material.density
+            {
+                candidate_cell.reset_settled();
+                self.cell.reset_settled();
+                self.set_cell(0, 0, candidate_cell);
                 self.set_cell(dx, dy, *self.cell);
+                self.swapped = true;
                 return true;
             }
         }
@@ -145,8 +146,6 @@ pub fn sim_tick_chunk(chunks: &mut [Option<&mut Chunk>; 9], seqno: u64) {
                     && cell.parity() == seqno_parity
                 {
                     cell.flip_parity();
-                    // apply the flipped parity in case the sim target doesn't
-                    set_cell(chunks, x, y, cell);
 
                     let mut update_ctx = UpdateCtx {
                         chunks,
@@ -160,9 +159,16 @@ pub fn sim_tick_chunk(chunks: &mut [Option<&mut Chunk>; 9], seqno: u64) {
 
                         // TODO this is platform-dependent, will break for multiplayer
                         rng: &mut rng,
+                        swapped: false,
                     };
 
                     update(&mut update_ctx);
+
+                    if !update_ctx.swapped {
+                        // the cell didn't move, so it's more settled, and we also need to update its state for parity
+                        cell.increment_settled();
+                        set_cell(chunks, x, y, cell);
+                    }
                 }
             }
         }
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