2 files changed, 65 insertions, 2 deletions

diff --git a/src/sim/materials/fire.rs b/src/sim/materials/fire.rs
new file mode 100644
index 0000000..b155986
--- /dev/null
+++ b/src/sim/materials/fire.rs
@@ -0,0 +1,53 @@
+use rand::RngExt;
+
+use crate::sim::{cell::Cell, materials::MaterialId, sim::UpdateCtx};
+
+trait FireCellView {
+    fn get_ticks_lived(self) -> u16;
+    fn set_ticks_lived(&mut self, ticks: u16) -> ();
+    fn is_flammable(self) -> bool;
+}
+
+impl FireCellView for Cell {
+    fn get_ticks_lived(self) -> u16 {
+        self.data
+    }
+    fn set_ticks_lived(&mut self, ticks: u16) -> () {
+        self.data = ticks;
+    }
+    // this could be a property of the material def, I think it's better here for now
+    fn is_flammable(self) -> bool {
+        [MaterialId::Wood].contains(&self.material)
+    }
+}
+
+#[inline]
+pub fn sim_update(ctx: &mut UpdateCtx) {
+    let ticks_lived = ctx.cell.get_ticks_lived();
+    // 2 seconds
+    if ticks_lived > 240 {
+        // kill ourselves, with a chance to turn into ash
+        if ctx.rng.random_range(0.0..1.0) > 0.8 {
+            // TODO ash material
+            ctx.set_cell(0, 0, Cell::from_material(MaterialId::Sand));
+        } else {
+            ctx.set_cell(0, 0, Cell::void());
+        }
+        return;
+    }
+
+    // 4 times in our lifespan, try to spread in a random direction
+    // since it's random, fire may die out if there's nothing in that direction
+    // a 1-thick line of flammable cells has a 31% chance to die each iteration
+    if ticks_lived % 60 == 0 {
+        let (dx, dy) = (ctx.rng.random_range(-1..=1), ctx.rng.random_range(-1..=1));
+        if let Some(target) = ctx.get_cell(dx, dy)
+            && target.is_flammable()
+        {
+            ctx.set_cell(dx, dy, Cell::from_material(MaterialId::Fire));
+        }
+    }
+
+    ctx.cell.set_ticks_lived(ticks_lived + 1);
+    ctx.set_cell(0, 0, *ctx.cell);
+}
diff --git a/src/sim/materials/mod.rs b/src/sim/materials/mod.rs
index d2d0e0e..764318a 100644
--- a/src/sim/materials/mod.rs
+++ b/src/sim/materials/mod.rs
@@ -1,5 +1,6 @@
 use crate::sim::sim::UpdateCtx;
 
+mod fire;
 mod gas;
 mod sand;
 mod water;
@@ -12,6 +13,7 @@ pub enum MaterialId {
     Wood,
     Water,
     Gas,
+    Fire,
 }
 
 pub struct MaterialDef {
@@ -21,7 +23,7 @@ pub struct MaterialDef {
     pub sim_update: Option<fn(ctx: &mut UpdateCtx) -> ()>,
 }
 
-static MATERIALS: [MaterialDef; 5] = [
+static MATERIALS: [MaterialDef; 6] = [
     MaterialDef {
         name: "Void",
         color: (0x00, 0x00, 0x00, 0x00),
@@ -52,15 +54,23 @@ static MATERIALS: [MaterialDef; 5] = [
         density: 10,
         sim_update: Some(gas::sim_update),
     },
+    MaterialDef {
+        name: "Fire",
+        color: (0xFC, 0x66, 0x00, 0xAA),
+        // for now this matches wood
+        density: 50,
+        sim_update: Some(fire::sim_update),
+    },
 ];
 
 impl MaterialId {
-    pub const ALL: [MaterialId; 5] = [
+    pub const ALL: [MaterialId; 6] = [
         MaterialId::Void,
         MaterialId::Sand,
         MaterialId::Wood,
         MaterialId::Water,
         MaterialId::Gas,
+        MaterialId::Fire,
     ];
     #[inline]
     pub fn def(self) -> &'static MaterialDef {