🌈 Rainbow Tower

A cute unicorn climbs an endless, rotating rainbow tower out of a candy sea. Cast rainbows to build your own platforms, bounce off elastics, grab a jetpack and fly, and climb as high as you can. The sea laps across the starting floor and never rises — but touch it once and the run is over.

Entry for the js13kGames 2026 competition — theme “Unicorns & Rainbows”. The whole game ships as a single self‑contained HTML file under 13 KB zipped (no assets, no dependencies at runtime).

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▶️ Play

Open src/index.html in any modern browser — the source is directly playable. For the competition build (minified + packed), run the build and open dist/index.html.

Controls

Action	Keyboard	Touch	Gamepad
Run around the tower	◄ ► / A D	drag left / right	stick / d‑pad ◄ ►
Jump (double‑jump in air)	↑ / W	tap / hold anywhere	A or d‑pad ▲
Cast a rainbow	Space / V	🌈 pad	B / X / Y
Open umbrella (slow fall)	hold ↑ / W after the double jump	keep holding	hold A
Dive (while flying)	↓ / S	swipe down	stick / d‑pad ▼
Mute	—	tap the 🔈 icon	—
Pause / resume	Esc	‖ button (top right)	Start
Menu: move / confirm	↑ ↓ / Space	tap a line	d‑pad ▲▼ / A

Pause

The title screen shows the controls for whatever you're actually holding: it detects a gamepad (and says so with a 🎮 badge), falls back to touch hints on a coarse‑pointer device, and shows keyboard hints otherwise. Unplug the pad and it switches back on the next frame.

Gamepads work with no setup. Browsers hide a pad until you press a button on it, so the first press just wakes it — the 🎮 badge appears on the title screen and nothing else happens; press again to start. (A page click or key press does not reveal a pad: it has to be the pad itself.) Stick and d‑pad both steer, and A doubles as "confirm" in the pause menu while d‑pad ▲▼ move the selection.

Esc (or the ‖ button next to the speaker, or Start) freezes the run and opens a menu with RESUME highlighted by default and QUIT TO MENU below it. Pick with ↑ ↓ and confirm with Space/Enter, or tap a line; Esc resumes from anywhere in the menu. Taps outside the two rows are ignored, so a stray thumb can't throw away a run.

Scoring

Every run is a fresh procedural tower, seeded from the clock. Height is the score, bonuses bank extra points, and a single all‑time best is kept locally (guarded localStorage, falling back to in‑memory).

Bonuses

• ⭐ Rainbow Rush — brief invincible rainbow storm with an unlimited magic gauge (casting costs nothing), ×2 score, and a safety net: if you fall with nothing below, a rainbow appears to catch you. Rainbows themselves behave exactly as they always do — same cooldown, same lifetime.
• 🚀 Rocket — one‑shot blast to the top of the screen, then a rainbow parachute floats you gently back down onto a platform.
• 🎒 Jetpack — a few seconds of free flight in any direction, invincible, twin thrusters spraying rainbow flame.

Platforms

Candy‑coloured ledges, horizontally moving platforms, spring elastics (bouncier the harder you land, with chain‑bounce momentum), and spike hazards.

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🛠 Run

nvm use && pnpm install && pnpm run dev

🛠 Build

nvm use && pnpm install && pnpm run build

The build:

1. extracts the game <script> from src/index.html,
2. minifies it with Terser (aggressive settings),
3. packs it with Roadroller (self‑extracting eval),
4. re‑inlines it into a minimal HTML shell (CSS + DOM are taken from the source, so there’s a single source of truth),
5. writes dist/index.html and zips it, printing the byte count against the 13 312 byte budget.

The zip step uses the zip CLI (macOS/Linux). On Windows, zip dist/index.html yourself, or wire in a Node zipper. For a few extra bytes on submission, run the final zip through [effect / advzip / ect] instead of plain zip -9.

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🎨 Cover & icon

Artwork lives in media/ and is generated, not hand-drawn — media/art.html redraws the game's own unicorn, rainbows and candy ledges on a canvas, and media/make.mjs screenshots it headlessly:

nvm use && node media/make.mjs

The two submission images are size-capped: media/shrink.py (python3 + Pillow) re-encodes them with a palette until they fit, and asserts the pixel dimensions never change. Everything is laid out inside an 8:5 safe area, so the 16:9 master and the 800×500 crop both keep the title fully visible.

File	Use
media/thumbnail-320x320.png	submission thumbnail — exactly 320×320, ≤64 KB
media/cover-800x500.png	submission cover — exactly 800×500, ≤256 KB
media/cover-1280x720.png	16:9 master cover
media/cover-1200x630.png	social / OG card
media/icon-512.png, icon-192.png	full-scene square icon
media/mark-512.png, apple-touch-icon.png	simplified mark (rainbow arc + horn)
media/favicon-32.png, favicon-16.png, favicon.ico	favicons

The in-game favicon costs no extra file: the game draws the same mark into a 32×32 canvas from its own BANDS palette at boot and sets it as the tab icon.

📁 Structure

rainbow-tower/
├── src/index.html      # readable, commented dev source — the single source of truth
├── build.mjs           # Terser + Roadroller pipeline
├── media/              # cover art, icons, favicons + the generator that draws them
├── package.json        # scripts: dev, build (pnpm)
├── .nvmrc              # pinned Node version
├── CLAUDE.md           # working notes for Claude Code
├── dist/               # build output (gitignored)
└── README.md

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🧩 Tech notes

• Fake‑3D cylinder — the world is a vertical cylinder. The hero stays centred at the front; moving rotates the tower. Points project with sx = W/2 + R·sin(a), depth d = cos(a), so ledges curve around the surface and dim toward the silhouette. No WebGL.
• Everything procedural — no image/audio assets. Art is canvas paths; sound is WebAudio: one bus with a feedback delay and a single noise buffer that every drum, whoosh and splash is filtered out of. Each action has its own voice (ground vs double jump, landing weight, casting, stomps that climb with the combo, springs that climb with the chain) and each power‑up gets a jingle. The music is an 8‑section chiptune with a swung 16th grid, a drum kit, and layers that unlock as you climb — intro, kit, breakdown, outro — going full and opening its filter during a Rainbow Rush, and ducking under the pause menu.
• Seeded RNG (mulberry32) drives the whole tower, so a run is fully determined by its seed.
• Local high scores via localStorage (guarded — falls back to in‑memory).
• Tuning — every feel knob lives in one CFG object at the top of the script (gravity, jump, rainbow arc, spring, colour decay, trail length…). Balance the game by editing numbers there, then rebuild to check the size.

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📦 Submitting to js13k

The competition weighs a zip ≤ 13 312 bytes containing index.html. nvm use && pnpm run build produces exactly that at dist/rainbow-tower.zip.

License

MIT © Nicolas Bonnici