4 files changed, 80 insertions, 23 deletions
diff --git a/src/sim/materials/fire.rs b/src/sim/materials/fire.rs
index b155986..3c686fe 100644
--- a/src/sim/materials/fire.rs
+++ b/src/sim/materials/fire.rs
@@ -21,25 +21,28 @@ impl FireCellView for Cell {
     }
 }
 
+// TODO optimize number of rng calls?
 #[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());
+        // we have a chance to live longer--roughly 50% chance of living an extra second
+        if ctx.rng.random_range(0.0..1.0) > 0.995 {
+            // 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;
         }
-        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 {
+    // at an average of 4 times per lifespan, try to spread
+    // 1/60 * 240 = 4
+    if ctx.rng.random_range(0.0..1.0) > (59.0 / 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()
@@ -48,6 +51,27 @@ pub fn sim_update(ctx: &mut UpdateCtx) {
         }
     }
 
+    // 8 times in our lifespan, emit smoke
+    if ticks_lived % 30 == 0 {
+        if let Some(target) = ctx.get_cell(0, -1)
+            && target.material == MaterialId::Void
+        {
+            for (dx, dy) in [
+                (0, -1),
+                (1 - ctx.seqno_parity as i32 * 2, 0),
+                (-1 + ctx.seqno_parity as i32 * 2, 0),
+                (0, 1),
+            ] {
+                if let Some(target) = ctx.get_cell(dx, dy)
+                    && target.material == MaterialId::Void
+                {
+                    ctx.set_cell(dx, dy, Cell::from_material(MaterialId::Smoke));
+                    break;
+                }
+            }
+        }
+    }
+
     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 764318a..10f0a06 100644
--- a/src/sim/materials/mod.rs
+++ b/src/sim/materials/mod.rs
@@ -3,6 +3,7 @@ use crate::sim::sim::UpdateCtx;
 mod fire;
 mod gas;
 mod sand;
+mod smoke;
 mod water;
 
 #[repr(u8)]
@@ -14,6 +15,7 @@ pub enum MaterialId {
     Water,
     Gas,
     Fire,
+    Smoke,
 }
 
 pub struct MaterialDef {
@@ -23,7 +25,7 @@ pub struct MaterialDef {
     pub sim_update: Option<fn(ctx: &mut UpdateCtx) -> ()>,
 }
 
-static MATERIALS: [MaterialDef; 6] = [
+static MATERIALS: [MaterialDef; 7] = [
     MaterialDef {
         name: "Void",
         color: (0x00, 0x00, 0x00, 0x00),
@@ -61,16 +63,23 @@ static MATERIALS: [MaterialDef; 6] = [
         density: 50,
         sim_update: Some(fire::sim_update),
     },
+    MaterialDef {
+        name: "Smoke",
+        color: (0x32, 0x35, 0x36, 0xAA),
+        density: 15,
+        sim_update: Some(smoke::sim_update),
+    },
 ];
 
 impl MaterialId {
-    pub const ALL: [MaterialId; 6] = [
+    pub const ALL: [MaterialId; 7] = [
         MaterialId::Void,
         MaterialId::Sand,
         MaterialId::Wood,
         MaterialId::Water,
         MaterialId::Gas,
         MaterialId::Fire,
+        MaterialId::Smoke,
     ];
     #[inline]
     pub fn def(self) -> &'static MaterialDef {
diff --git a/src/sim/materials/smoke.rs b/src/sim/materials/smoke.rs
new file mode 100644
index 0000000..68f77ca
--- /dev/null
+++ b/src/sim/materials/smoke.rs
@@ -0,0 +1,24 @@
+use rand::RngExt;
+
+use crate::sim::{cell::Cell, materials::MaterialId, sim::UpdateCtx};
+
+#[inline]
+pub fn sim_update(ctx: &mut UpdateCtx) {
+    // only allow upward movement some of the time to limit movement speed
+    if ctx.rng.random_range(0.0..1.0) > 0.8 {
+        if ctx.candidates_swap(&[(0, -1)]) {
+            return;
+        }
+    }
+    // same for each horizontal direction
+    if ctx.rng.random_range(0.0..1.0) > 0.8 {
+        if ctx.candidates_swap(&[(1 - ctx.seqno_parity as i32 * 2, 0)]) {
+            return;
+        }
+    }
+    if ctx.rng.random_range(0.0..1.0) > 0.8 {
+        if ctx.candidates_swap(&[(-1 + ctx.seqno_parity as i32 * 2, 0)]) {
+            return;
+        }
+    }
+}
diff --git a/src/sim/materials/water.rs b/src/sim/materials/water.rs
index d76ec5b..1ba8eb4 100644
--- a/src/sim/materials/water.rs
+++ b/src/sim/materials/water.rs
@@ -62,15 +62,15 @@ pub fn sim_update(ctx: &mut UpdateCtx) {
 
     // we didn't find a hole, so just move "randomly" on the same surface
     // TODO when to settle?
-    let target_x = if !can_move_left {
-        1
-    } else if !can_move_right {
-        -1
-    } else if ctx.seqno_parity % 2 == 1 {
-        1
-    } else {
-        -1
-    };
+    // let target_x = if !can_move_left {
+    //     1
+    // } else if !can_move_right {
+    //     -1
+    // } else if ctx.seqno_parity % 2 == 1 {
+    //     1
+    // } else {
+    //     -1
+    // };
 
-    ctx.candidates_swap(&[(target_x, 0)]);
+    // ctx.candidates_swap(&[(target_x, 0)]);
 }