From 69f0407637a071d79d73115e4ae9c0ab526066a7 Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Thu, 13 Aug 2026 21:31:53 -0700
Subject: parallelization

---
 src/main.rs | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

(limited to 'src/main.rs')

diff --git a/src/main.rs b/src/main.rs
index b048122..313a7a8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -7,6 +7,7 @@ use egui::Id;
 use egui_wgpu::{RendererOptions, ScreenDescriptor};
 use egui_winit::egui::{self, Context};
 use pixels::{Pixels, ScalingMode, SurfaceTexture};
+use rand::random_range;
 use std::time::{Duration, Instant};
 use winit::{
     application::ApplicationHandler,
@@ -30,10 +31,10 @@ pub type Error = Box<dyn std::error::Error>;
 pub type Result<T> = std::result::Result<T, Error>;
 
 struct Config {
-    show_ticks: bool,
     fps: u16,
     brush_radius: u8,
     brush_material: MaterialId,
+    use_threading: bool,
 }
 
 struct Input {
@@ -118,7 +119,7 @@ impl Default for App {
 
             config: Config {
                 fps: 120,
-                show_ticks: false,
+                use_threading: true,
                 brush_radius: 10,
                 brush_material: MaterialId::Sand,
             },
@@ -270,24 +271,26 @@ impl ApplicationHandler for App {
                         // 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 {
-                                // brush/selection
+                                let r = random_range(0.0..1.0);
                                 if ((x - lm.0).pow(2) + (y - lm.1).pow(2))
                                     < (self.config.brush_radius as i32).pow(2)
+                                    && r > 0.9
                                 {
+                                    let mut cell = Cell::from_material(self.config.brush_material);
+                                    cell.flags = (self.sim_seqno as u8) & 0b1;
                                     world.set_cell_from_game_position(
-                                        x,
-                                        y,
-                                        Cell::from_material(self.config.brush_material),
+                                        x, y, cell, // wake the chunk
+                                        false,
                                     );
                                 }
                             }
                         }
                     }
 
-                    // TODO check if we need to run another sim tick given the sim speed
+                    // TODO check if we need to run another sim tick given the sim speed + delta_time
                     // SIM logic
                     if !self.sim_paused || self.ignore_pause_next_tick {
-                        sim_tick(world, self.sim_seqno);
+                        sim_tick(world, self.sim_seqno, self.config.use_threading);
                         self.sim_seqno += 1;
                         self.ignore_pause_next_tick = false;
                     }
-- 
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