# Falling Sand Simulation 🧱✨

A high-performance, modular falling sand physics sandbox built in vanilla JavaScript and HTML5 Canvas. Experience realistic particulate physics, fluid dynamics, thermodynamics, combustion, and chemical reactions running at a silky-smooth 60+ FPS.

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## ⚡ Performance & Engine Architecture

* **Direct 32-Bit Pixel Blitter (`Uint32Array` / `ImageData`):**
  Replaces traditional Canvas 2D `fillRect` / `arc` draw calls with direct memory writes into a 32-bit RGBA pixel buffer on an offscreen buffer canvas, delivering a **50x–100x rendering speedup** that comfortably handles hundreds of thousands of active particles.
* **Rapid Fluid Dispersion:**
  Liquids (water, acid, oil) dynamically disperse up to customizable multi-cell horizontal steps per frame, eliminating gelatinous stacking and delivering realistic splashing and surface leveling.
* **Oil & Water Emulsion & Separation:**
  Water and oil mix dynamically with diagonal and horizontal swapping before buoyantly separating out according to density.
* **Lava & Rock Sinking:**
  Dense molten lava plunges into water, boiling it into rising steam, and solidifies into stone that naturally sinks through liquid to the bottom of the pool.
* **Monotonic Frame Counter & Alternating Sweep:**
  Eliminates the legacy full-grid `updated = false` pass. Cells track `lastUpdated = currentFrame`. The simulation loop alternates horizontal scan direction (left-to-right vs. right-to-left) every frame to eliminate asymmetric pile-up bias in liquids and sand.
* **Zero-Allocation Hot Loop:**
  All neighbor evaluations, directional offsets, and particle physics run with zero heap allocations or closures, preventing garbage collection pauses and stuttering.
* **Bresenham Stroke Interpolation:**
  Uses Bresenham's line algorithm between consecutive cursor samples to ensure smooth, gapless lines even when drawing at high speeds.
* **Non-Destructive Canvas Resizing:**
  Resizing the window or changing device orientation preserves existing particles on the canvas rather than wiping the simulation.

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## 🧪 Element & Reaction Ecosystem

| Element | Category | Behavior & Unique Reactions |
| :--- | :--- | :--- |
| **Sand** | Solid | Granular physics; forms realistic dunes; sinks through liquids. |
| **Dirt** | Solid | Rich earthen soil; supports plant and grass roots; displaceable by explosions. |
| **Rock** | Solid | Heavy barrier; holds back blasts; naturally sinks through liquids to form riverbeds. |
| **Wood** | Solid | Rigid structural block; flammable when exposed to fire or lava. |
| **Ice** | Solid | Crystalline cold block; slowly freezes touching water; melts near heat/fire/lava. |
| **Water** | Liquid | Flows rapidly; mixes with and separates from oil; turns lava into rock; boils into steam. |
| **Lava** | Liquid | Heavy molten magma; plunges into water boiling it into steam; cools into solid rock. |
| **Oil** | Liquid | Viscous flammable liquid; mixes with water and then floats to the surface; catches fire intensely. |
| **Acid** | Liquid | Corrosive fluid; fast dispersion; sinks through lighter liquids; dissolves organics, metals, and earth. |
| **Plant** | Organics | Grows upwards towards light; absorbs water; turns into wood under vertical load. |
| **Grass** | Organics | Colonizes surface dirt and sand; sprouts blades; accelerates with moisture. |
| **Fire** | Gas / Energy | Dynamic temperature shading (yellow $\rightarrow$ orange $\rightarrow$ red); ignites flammables; spawns smoke. |
| **Steam** | Gas | Rises through atmosphere and liquids; escapes into the sky or condenses back into water. |
| **Smoke** | Gas | Produced by fires, explosions, and burning oil; drifts with air turbulence and dissipates. |
| **TNT** | Energetic | Detonates from fire, lava, or acid; clusters into unified blast waves launching particles kinetically. |
| **Eraser** | Tool | Clears cells within brush radius; also accessible via right-click drag. |

---

## 🎮 Controls & Shortcuts

| Action | Control |
| :--- | :--- |
| **Draw Element** | `Left Click` + Drag / Touch |
| **Erase** | `Right Click` + Drag or select **Eraser** |
| **Brush Size** | `Mouse Wheel` or `[` / `]` or Drawer Slider |
| **Pause / Play** | `Spacebar` or Pause button (⏸ / ▶) |
| **Single Frame Step** | `S` or `.` (Period) or Step button (⏭) |
| **Clear Canvas** | Clear button in Elements drawer |

---

## ⚙️ Configuration & Customization

All simulation and material parameters can be tuned in real time via the **Settings ⚙️** drawer:
* **Time & Global:** Simulation speed (0–20), gravity (-1.0 to 2.0), air drag (0.1 to 1.0).
* **Explosive:** Blast force, blast reach, plus independent destruction toggles for Rock, Wood, Dirt, Sand, Plant, Grass, Water, Acid, Ice, Lava, and Oil.
* **Acid:** Dissolve rate, sink rate, spread speed, explode TNT toggle, plus independent dissolve toggles for Rock, Wood, Dirt, Sand, Plant, Grass, Water (infection), Ice, and Oil.
* **Water:** Flow rate and horizontal spread speed (dispersion).
* **Lava:** Flow rate, spread speed, cooling rate, and water sink rate.
* **Oil:** Flow rate, spread speed, burn rate, water sink rate, and oil float rate.
* **Ice:** Melt rate and freeze rate.
* **Fire, Steam & Smoke:** Fire decay rate, condensation rate, and smoke dissipation rate.
* **Plant & Grass:** Growth rate, woodification rate, and burn rate.
* **Visuals:** Switch between `blocky`, `fuzzy` (filtered bloom), or `bloby` rendering, and toggle multi-tone grain color noise.
* Settings are automatically saved to `localStorage` and can be restored using **Reset to Defaults**.

---

## 📂 Project Structure

```text
├── index.html        # HTML5 entrypoint with drawers and canvas
├── index.css         # Glassmorphic dark UI design and responsive styles
├── index.js          # Main initialization loop, event loop, and input wiring
├── config.js         # Config defaults, settings persistence, and schema
├── state.js          # Grid buffers, canvas dimensions, brush, and frame counter
├── actions.js        # Atomic grid operations (move, swap) with frame tagging
├── renderer.js       # Fast 32-bit Uint32Array blitter with cursor overlay
├── physics.js        # Simulation loop dispatcher and particle generation
├── dirt.js           # Granular sand and soil physics with liquid displacement
├── water.js          # Fast fluid dynamics, oil mixing/separation, and plant hydration
├── lava.js           # Dense molten thermodynamics, water penetration, and rock formation
├── oil.js            # Flammable buoyant liquid physics with water emulsion/separation
├── ice.js            # Freezing and melting thermal logic
├── acid.js           # Fast-spreading corrosive fluid, sinking, and dissolution physics
├── fire.js           # Combustion, heat transfer, temperature decay, and smoke emission
├── steam.js          # Atmospheric rising and condensation
├── smoke.js          # Rising particulate dispersion and decay
├── plant.js          # Root propagation, woodification, and phototropism
├── grass.js          # Surface dirt colonization and blade growth
├── explosive.js      # Clustered BFS blast waves and kinetic shockwaves
└── ui.js             # Categorized elements palette, Bresenham strokes, and settings drawer
```

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## 🚀 Getting Started

No build step or external dependencies are required. Simply serve the directory with any local static HTTP server:

```bash
# Using Python
python -m http.server 8080

# Using Node.js (npx)
npx serve .
```

Open `http://localhost:8080` in any modern web browser.