feat: add heat, steam, and temperature-based fire

.gitignore

@@ -6,3 +6,6 @@ node_modules
 AGENTS.md
 DESIGN.md
 TASKS.md
+docs/
+.agents
+skills-lock.json

README.md

@@ -30,9 +30,10 @@ unit-testable with plain `cargo test`.
 | Sand         | Falls and piles; sinks through water        |
 | Water        | Flows and spreads                           |
 | Stone        | Static obstacle                             |
-| Fire         | Rises, flickers, burns out                  |
-| Wood         | Static; ignites from adjacent fire          |
-| Erase / Clear | Remove cells                               |
+| Fire         | Rises, flickers, burns out; heats neighbors             |
+| Wood         | Static; ignites when heat reaches 80                    |
+| Steam        | Rises; condenses when cool; water boils next to fire    |
+| Erase / Clear | Remove cells                                           |
 
 ## Quickstart
 

index.html

@@ -101,6 +101,9 @@ <h1>Sandboxed</h1>
       <button data-mat="5">
         <span class="swatch" style="background: #764824"></span>Wood
       </button>
+      <button data-mat="6">
+        <span class="swatch" style="background: #d8dce8"></span>Steam
+      </button>
       <button data-mat="0">
         <span class="swatch" style="background: #1a1a24"></span>Erase
       </button>

src/lib.rs

@@ -49,7 +49,7 @@ impl Simulation {
         self.world.height
     }
 
-    /// Paint `material` (0=erase, 1=sand, 2=water, 3=stone, 4=fire, 5=wood) at (x, y).
+    /// Paint `material` (0=erase, 1=sand, 2=water, 3=stone, 4=fire, 5=wood, 6=steam) at (x, y).
     pub fn paint(&mut self, x: usize, y: usize, material: u8, radius: usize) {
         if let Some(cell) = Cell::from_u8(material) {
             self.world.paint(x, y, cell, radius);

src/renderer.rs

@@ -19,22 +19,44 @@ fn put(frame: &mut [u8], i: usize, r: i16, g: i16, b: i16) {
     frame[o + 3] = 255;
 }
 
+fn warm(r: i16, g: i16, b: i16, heat: u8) -> (i16, i16, i16) {
+    let t = heat as i16;
+    (r + t / 2, g, b.saturating_sub(t / 3))
+}
+
 /// Write the whole world into `frame` (must be width*height*4 bytes).
 pub fn draw(world: &World, frame: &mut [u8]) {
     for (i, cell) in world.cells().iter().enumerate() {
         let x = i % world.width;
         let y = i / world.width;
         let j = jitter(x, y);
+        let h = world.heat()[i];
         match cell {
             Cell::Empty => put(frame, i, 12, 12, 18),
-            Cell::Sand => put(frame, i, 194 + j, 168 + j, 96 + j / 2),
-            Cell::Water => put(frame, i, 40, 90 + j, 200 + j),
-            Cell::Stone => put(frame, i, 110 + j / 2, 110 + j / 2, 118),
+            Cell::Sand => {
+                let (r, g, b) = warm(194 + j, 168 + j, 96 + j / 2, h);
+                put(frame, i, r, g, b);
+            }
+            Cell::Water => {
+                let (r, g, b) = warm(40, 90 + j, 200 + j, h);
+                put(frame, i, r, g, b);
+            }
+            Cell::Stone => {
+                let (r, g, b) = warm(110 + j / 2, 110 + j / 2, 118, h);
+                put(frame, i, r, g, b);
+            }
             Cell::Fire => {
                 let t = world.ttl()[i] as i16;
                 put(frame, i, 255, 32 + t * 4, 16);
             }
-            Cell::Wood => put(frame, i, 118 + j / 2, 72 + j / 2, 36),
+            Cell::Wood => {
+                let (r, g, b) = warm(118 + j / 2, 72 + j / 2, 36, h);
+                put(frame, i, r, g, b);
+            }
+            Cell::Steam => {
+                let (r, g, b) = warm(216 + j / 2, 220 + j / 2, 232, h);
+                put(frame, i, r, g, b);
+            }
         }
     }
 }
@@ -44,6 +66,37 @@ mod tests {
     use super::*;
     use crate::world::{Cell, World};
 
+    #[test]
+    fn steam_pixels_are_pale() {
+        let mut world = World::new(1, 1);
+        world.paint(0, 0, Cell::Steam, 0);
+        let mut frame = vec![0u8; 4];
+        draw(&world, &mut frame);
+        let (r, g, b) = (frame[0], frame[1], frame[2]);
+        assert!(
+            r > 180 && g > 180 && b > 180,
+            "expected pale steam, got {r},{g},{b}"
+        );
+        assert_eq!(frame[3], 255);
+    }
+
+    #[test]
+    fn hot_wood_is_warmer_than_cold_wood() {
+        let mut cold = World::new(1, 1);
+        cold.paint(0, 0, Cell::Wood, 0);
+        let mut hot = World::new(1, 1);
+        hot.paint(0, 0, Cell::Wood, 0);
+        hot.add_heat_for_test(0, 0, 70);
+        let mut fc = vec![0u8; 4];
+        let mut fh = vec![0u8; 4];
+        draw(&cold, &mut fc);
+        draw(&hot, &mut fh);
+        assert!(
+            fh[0] > fc[0] || fh[2] < fc[2],
+            "hot wood should be redder or less blue: cold={fc:?} hot={fh:?}"
+        );
+    }
+
     #[test]
     fn fire_pixels_are_orange_red() {
         let mut world = World::new(2, 1);