feat: air field, fans, and gunpowder shockwaves

README.md

@@ -33,6 +33,8 @@ unit-testable with plain `cargo test`.
 | Fire         | Rises, flickers, burns out; heats neighbors             |
 | Wood         | Static; ignites when heat reaches 80                    |
 | Steam        | Rises; condenses when cool; water boils next to fire    |
+| Fan          | Static; click the swatch to cycle facing; blows gases in that 4×4 |
+| Gunpowder    | Falls like sand; explodes from fire or heat 80                    |
 | Erase / Clear | Remove cells                                           |
 
 ## Quickstart

index.html

@@ -104,6 +104,12 @@ <h1>Sandboxed</h1>
       <button data-mat="6">
         <span class="swatch" style="background: #d8dce8"></span>Steam
       </button>
+      <button id="fan" data-mat="7">
+        <span class="swatch" style="background: #5a6e96"></span>Fan →
+      </button>
+      <button data-mat="11">
+        <span class="swatch" style="background: #28241e"></span>Gunpowder
+      </button>
       <button data-mat="0">
         <span class="swatch" style="background: #1a1a24"></span>Erase
       </button>
@@ -143,15 +149,29 @@ <h1>Sandboxed</h1>
       let paused = false;
       let pendingStep = false;
 
+      const FAN_MATS = [7, 8, 9, 10];
+      const FAN_LABELS = ["Fan →", "Fan ←", "Fan ↑", "Fan ↓"];
+      const fanBtn = document.getElementById("fan");
+
+      const setActive = (btn) => {
+        document
+          .querySelectorAll("#palette button")
+          .forEach((b) => b.classList.remove("active"));
+        btn.classList.add("active");
+      };
+
       document
         .querySelectorAll("#palette button[data-mat]")
         .forEach((btn) => {
           btn.addEventListener("click", () => {
+            if (btn === fanBtn && Number(fanBtn.dataset.mat) === material) {
+              const i = FAN_MATS.indexOf(material);
+              const n = (i + 1) % 4;
+              fanBtn.dataset.mat = String(FAN_MATS[n]);
+              fanBtn.innerHTML = `<span class="swatch" style="background: #5a6e96"></span>${FAN_LABELS[n]}`;
+            }
             material = Number(btn.dataset.mat);
-            document
-              .querySelectorAll("#palette button")
-              .forEach((b) => b.classList.remove("active"));
-            btn.classList.add("active");
+            setActive(btn);
           });
         });
 

src/lib.rs

@@ -49,7 +49,8 @@ impl Simulation {
         self.world.height
     }
 
-    /// Paint `material` (0=erase, 1=sand, 2=water, 3=stone, 4=fire, 5=wood, 6=steam) at (x, y).
+    /// Paint `material` (0=erase, 1=sand, 2=water, 3=stone, 4=fire, 5=wood,
+    /// 6=steam, 7=fan→, 8=fan←, 9=fan↑, 10=fan↓, 11=gunpowder) 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

@@ -1,6 +1,6 @@
 //! Converts the world grid into an RGBA frame buffer for the browser.
 
-use crate::world::{Cell, World};
+use crate::world::{Cell, World, AIR_CELL};
 
 /// Deterministic per-pixel color jitter so large piles look textured
 /// instead of flat. Uses a cheap integer hash of (x, y).
@@ -32,7 +32,12 @@ pub fn draw(world: &World, frame: &mut [u8]) {
         let j = jitter(x, y);
         let h = world.heat()[i];
         match cell {
-            Cell::Empty => put(frame, i, 12, 12, 18),
+            Cell::Empty => {
+                let ai = (y / AIR_CELL) * world.air_w + (x / AIR_CELL);
+                let avx = world.vx()[ai];
+                let avy = world.vy()[ai];
+                put(frame, i, 12 + avx / 2, 12 - avx / 2, 18 + avy / 2);
+            }
             Cell::Sand => {
                 let (r, g, b) = warm(194 + j, 168 + j, 96 + j / 2, h);
                 put(frame, i, r, g, b);
@@ -57,6 +62,14 @@ pub fn draw(world: &World, frame: &mut [u8]) {
                 let (r, g, b) = warm(216 + j / 2, 220 + j / 2, 232, h);
                 put(frame, i, r, g, b);
             }
+            Cell::FanRight => put(frame, i, 110, 120, 150),
+            Cell::FanLeft => put(frame, i, 70, 100, 140),
+            Cell::FanUp => put(frame, i, 90, 130, 160),
+            Cell::FanDown => put(frame, i, 90, 100, 120),
+            Cell::Gunpowder => {
+                let (r, g, b) = warm(40 + j / 2, 36 + j / 2, 32, h);
+                put(frame, i, r, g, b);
+            }
         }
     }
 }
@@ -107,4 +120,38 @@ mod tests {
         assert!(r > g && g > b, "expected orange/red, got {r},{g},{b}");
         assert_eq!(frame[3], 255);
     }
+
+    #[test]
+    fn empty_pixel_tints_when_fan_blows() {
+        let still = World::new(8, 8);
+        let mut blown = World::new(8, 8);
+        blown.paint(0, 0, Cell::FanRight, 0);
+        blown.step();
+        let mut fs = vec![0u8; 8 * 8 * 4];
+        let mut fb = vec![0u8; 8 * 8 * 4];
+        draw(&still, &mut fs);
+        draw(&blown, &mut fb);
+        // Pixel (3, 0) is Empty in both; in blown it shares the fan's air cell.
+        let o = (0 * 8 + 3) * 4;
+        let (sr, sg, sb) = (fs[o], fs[o + 1], fs[o + 2]);
+        let (br, bg, bb) = (fb[o], fb[o + 1], fb[o + 2]);
+        assert!(
+            br > sr && bg < sg,
+            "FanRight should redden (+vx) and green-shift down (−vx): still=({sr},{sg},{sb}) blown=({br},{bg},{bb})"
+        );
+        assert_eq!(fb[o + 3], 255);
+    }
+
+    #[test]
+    fn gunpowder_pixels_are_dark() {
+        let mut world = World::new(1, 1);
+        world.paint(0, 0, Cell::Gunpowder, 0);
+        let mut frame = vec![0u8; 4];
+        draw(&world, &mut frame);
+        let (r, g, b) = (frame[0], frame[1], frame[2]);
+        assert!(
+            r < 80 && g < 80 && b < 80,
+            "expected charcoal, got {r},{g},{b}"
+        );
+    }
 }