From 820e4d00837376bc63b614a382809469a719ed0b Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Sun, 23 Aug 2026 22:48:38 -0700
Subject: entity partitioning

---
 src/sim/sim_manager/mod.rs | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

(limited to 'src/sim/sim_manager/mod.rs')

diff --git a/src/sim/sim_manager/mod.rs b/src/sim/sim_manager/mod.rs
index 8fab9cf..b2441ef 100644
--- a/src/sim/sim_manager/mod.rs
+++ b/src/sim/sim_manager/mod.rs
@@ -1,12 +1,14 @@
 use std::time::Instant;
 
 use fxhash::FxHashMap;
+use rand::random_range;
 
 use crate::{
     Config, InputManager,
     config::{PHYSICS_DELTA_TIME, PHYSICS_FPS, SIM_FPS},
     input::Input,
     sim::{
+        cell::Cell,
         cell_manager::manager::CellManager,
         entity::{Entity, EntityDef, EntityId},
         particle_manager::ParticleManager,
@@ -99,6 +101,41 @@ impl SimManager {
         // before we tick, write all the entities into the sim world
         let cells_written_by_entity = write_entities_to_world(self);
 
+        // --TEST DRAWING--
+        if input_manager.lmb_held || input_manager.rmb_held {
+            // start with the bounding box of the drawing brush circle + some margin
+            // clamp the bounding box to the board sie
+            let bb_xl = (input_manager.world_mouse_pos.x - config.brush_radius).round() as i32;
+            let bb_xu = (input_manager.world_mouse_pos.x + config.brush_radius).round() as i32;
+            let bb_yl = (input_manager.world_mouse_pos.y - config.brush_radius).round() as i32;
+            let bb_yu = (input_manager.world_mouse_pos.y + config.brush_radius).round() as i32;
+
+            // for each point, check if the distance is less than the brush size and write the pixel
+            for x in bb_xl..bb_xu {
+                for y in bb_yl..bb_yu {
+                    let r = random_range(0.0..1.0);
+                    if ((x - input_manager.world_mouse_pos.x.round() as i32).pow(2)
+                        + (y - input_manager.world_mouse_pos.y.round() as i32).pow(2))
+                        < (config.brush_radius as i32).pow(2)
+                        && r > 0.9
+                    {
+                        let cell = if input_manager.lmb_held {
+                            let mut cell = Cell::from_material(config.brush_material);
+                            // ensure we simulate on the first tick
+                            cell.match_parity(self.cell_manager.seqno);
+                            cell
+                        } else {
+                            Cell::void()
+                        };
+
+                        self.cell_manager.set_cell_from_game_position(
+                            x, y, cell, false, // wake the chunk
+                        )
+                    }
+                }
+            }
+        }
+
         // tick
         self.cell_manager.tick(config.use_threading);
 
-- 
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