# Physilinks

Physilinks is a browser-based physics linking game built with Matter.js. Match and chain same-colored falling balls; link enough to clear them and rack up points.

## Play instructions
- Open `index.html` in a modern browser (desktop or mobile touch).
- Choose a scene from the selector (changes gravity, obstacles, spawn rate, palette, ball size). Switching scenes restarts the run.
- Click/touch a ball to start a chain; drag through balls of the same color to add them. Drag back to the previous ball to undo the last link.
- Release: if the chain length is below the minimum, links vanish; if it meets/exceeds the minimum, linked balls are cleared and you score `10 × length²` (popup shows the gain).
- The top is open; if a new ball cannot enter because the entry is blocked, the run ends. The overlay shows final score with a restart button.
- Pause/resume with the button or `Esc`. HUD shows spawn rate, min link, chain length, score, per-scene high score, and palette legend.

## Tech notes
- **Engine**: Matter.js (via CDN). Canvas rendering with custom overlays for HUD, pause, game over, and score popups.
- **Scenes**: Defined in `src/scenes/*.js` as presets (config + `createBodies` factory). Applying a scene updates gravity, spawn rate, ball radius, palette, link constraints (stiffness/stretch/damping/width), and static bodies, then restarts the game.
- **Physics entities**: Falling balls (`Bodies.circle`) with gentle restitution/friction; static boundaries/obstacles per scene. The top is open; sides and floor are static bodies.
- **Input**: Pointer/touch events mapped to scene coords; chain state tracks bodies and a dashed preview line to the pointer. Undo by dragging back to the previous node.
- **Scoring**: `10 × length²` per cleared chain. Score popup rendered as DOM element near release point (via UI module).
- **Persistence**: Per-scene high score stored in `localStorage` under `physilinks-highscore-<sceneId>`; loaded on scene change; HUD shows current scene's best.
- **Game loop**: Single Matter runner controlled in `main.js`, with spawning handled by `src/spawn.js` and goal messaging handled by `src/goals.js`. Pause/game over stop the runner and spawner and zero `engine.timing.timeScale` so physics and rotating obstacles freeze; resume restarts the runner and spawner.
- **Lose detection**: Spawned balls monitor entry; if they remain near the spawn zone with negligible velocity after a short delay, the run is over.

## File structure
- `index.html`: Shell layout and HUD overlays; loads Matter.js plus game scripts.
- `styles.css`: Styling for canvas, HUD, overlays, and score popups.
- `src/scenes/`: Scene presets split per file (`scene-*.js`) plus `index.js` that registers them to `window.PhysilinksScenes` (e.g., zero-G grid, balanced, low-G, fast drop, lava drift).
- `src/scenes/scene-template.js`: Reference-only template documenting every scene config option; not loaded by default.
- `src/config.js`: Base game config defaults (gravity, spawn timing, link settings, palettes, message defaults).
- `src/engine.js`: Matter engine/render/runner setup helpers (create, start/stop runner, resize render).
- `src/decomp-setup.js`: Registers `poly-decomp` with Matter to allow concave shapes (stars, blobs) built via `Bodies.fromVertices`.
- `src/ui.js`: DOM access, HUD updates, overlays, popups, and control/selector wiring.
- `src/spawn.js`: Spawner utilities (intervals, batch/column/grid spawns), ball creation (shapes/blobs), radius scaling, and blob cleanup.
- `src/goals.js`: Goal computation and messaging (timer/score/clear/color goals, milestone announcements, intro message).
- `src/input.js`: Pointer/touch handling, drag constraints, chain linking/undo flow, and input event wiring.
- `src/main.js`: Physics setup, state machine, chain interaction, scene application, and pause/restart logic; delegates spawn duties to `src/spawn.js`, goal handling to `src/goals.js`, and input/chain interactions to `src/input.js`.

## Development quick start
- No build step. Open `index.html` directly in the browser.
- Key files: `index.html` (layout), `styles.css` (styling), `src/ui.js` (DOM/HUD), `src/main.js` (physics/game logic), `src/scenes/index.js` (scene registration).
- Adjust or add scenes by extending the files in `src/scenes/` with config and a `createBodies(width, height)` function.

## Adding a new scene
- Create `src/scenes/scene-<your-id>.js` based on `src/scenes/scene-template.js` or an existing scene, and keep the `id` aligned to the filename suffix.
- Add the script tag to `index.html` with the other scene files so it loads in the browser.
- Register the scene id in `src/scenes/index.js` (append to `desiredOrder` or rely on the unordered fallback).
- If the scene uses new DOM ids/classes or storage keys, document them in your commit notes per the repo guidelines.