game

name	game
description	Autonomous browser game agent. Analyzes game concept, implements with KAPLAY.js (2D) or Three.js (3D), playtests in headless browser, critiques gameplay/mechanics, fixes, and launches the result.

Game Agent

Use this skill to create browser-based games using KAPLAY.js (2D) or Three.js (3D) with a focus on playable mechanics, clear feedback, and polished feel.

Workflow

Follow this strict loop when asked to create a game:

Phase 1: Bootstrap

1. Check Context: If package.json is missing, run bash .claude/skills/game/scripts/setup.sh.
2. Scaffold: Ensure index.html and src/game.js exist (or inline in index.html).
3. Read API Reference:
   • For 2D games: Read references/kaplay-ref.md for KAPLAY API.
   • For 3D games: Read references/threejs-ref.md for Three.js API.
   • For FPS games: Read references/fps-patterns.md for pointer lock, hit detection, enemy AI.
4. Read Game Patterns: Read references/game-patterns.md for architecture patterns.
5. Read Game Systems: Read references/game-systems.md for difficulty scaling, scoring, persistence, and UI patterns.
6. Read Visual Assets: Read references/visual-assets.md for procedural sprites, palettes, and visual effects.

Phase 1.5: Game Design Analysis (Before Coding!)

This game needs to be playable and fun from the first iteration. Therefore, define the core loop before writing any code.

Before writing any code, decompose the game:

1. Identify the Core Mechanic: What is the ONE thing the player does repeatedly?

   • Strip away everything else first
   • This mechanic must be satisfying on its own
   • Examples: jump, shoot, match, dodge, collect, solve

2. Define the Challenge: What makes it difficult?

   • Timing? Precision? Resource management? Puzzle solving?
   • How does difficulty progress?
   • What's the failure state?

3. Establish the Feedback Loop:

   • Input: What does the player press/click/drag?
   • Response: What happens immediately? (must feel < 100ms)
   • Outcome: Success or failure indication
   • Reward/Penalty: Score change, sound, visual effect

4. Scope to Minimum Viable Game (MVG):

   • ONE level or endless mode
   • ONE enemy type or obstacle
   • ONE player ability
   • Win AND lose conditions
   • Can be expanded later, but MVG must work first

5. Research the Domain (for educational/simulation games):

   • Look up actual facts (angles, counts, formulas, rules)
   • Don't guess scientific/mathematical details
   • See references/physics-constants.md for common values

Phase 1.6: Game Feel Principles

6. Juice: The game must feel alive and responsive.

   • Input Response: Every input produces immediate visual/audio feedback
   • Screen Shake: On impacts, collisions, explosions - use shake(intensity)
   • Flash: Brief color flash on damage or success - use flash(color, duration)
   • Particles: On deaths, pickups, actions (spawn small objects with lifespan)
   • Squash & Stretch: Scale objects on jumps, bounces, movements

7. Clarity: The player must always understand:

   • Where they are (player position obvious, distinct color/shape)
   • What they can do (affordances clear)
   • What hurts them (dangers visually distinct - red, spiky, animated)
   • What helps them (pickups/goals highlighted - gold, glowing, animated)
   • Current state (score, lives, progress visible in HUD)

8. Pacing: Control the rhythm

   • Moments of tension followed by release
   • Difficulty curves, not walls
   • Rest points between challenges
   • Even endless games need rhythm variation (spawn rate waves)

9. Polish Details:

   • Title/start screen with game name and controls
   • Pause functionality (P key or Escape)
   • Restart on game over (R key)
   • Score or progress display (top-left, fixed() for HUD)
   • Control hints visible ("Arrow keys: Move | Space: Jump")

Phase 1.7: Physics & Reachability Validation

CRITICAL: Validate that game physics allow the player to accomplish required actions.

16. Test Core Movement: Before finalizing level/game design:

    • Can the player reach all required locations?
    • Can the player avoid all avoidable hazards?
    • Does movement feel responsive (not sluggish or twitchy)?
    • Are speeds balanced (player vs enemies vs projectiles)?

17. Validate With Math: For physics-based games, calculate limits:

    • Movement range per second = speed × time
    • Jump/launch height = (force)² / (2 × gravity)
    • Projectile range = speed × lifetime
    • If design requires X, verify physics allow X

18. Common Physics Pitfalls:

    • Targets placed beyond movement range
    • Gaps larger than jump/dash distance
    • Enemies faster than player can react
    • Timers shorter than required actions
    • Always prototype movement before building levels

Phase 1.8: Visual Polish (Before Coding!)

CRITICAL: Games must look polished from the first iteration. No "sticks and boxes."

Quality Bar: Ask yourself - "Would someone pay $5 for this?" If not, it's not ready.

10. Choose a Color Palette: Select from visual-assets.md palettes:

    • PASTEL - friendly, casual games
    • PICO8 - retro pixel art feel
    • ENDESGA - modern indie aesthetic
    • NEON - cyberpunk, arcade style

11. Generate PREMIUM Procedural Sprites: Every sprite needs MULTIPLE layers of polish:

    • Player/Hero: outer glow + multi-stop gradient + shadow + character details (eyes, expression) + highlights
    • Collectibles: glow aura + metallic/shiny gradient + inner detail + shine streak + sparkle accents
    • Enemies/Hazards: danger glow + gradient body + expressive features + shadow + distinguishing details
    • Environment (platforms, walls, tiles): surface texture + body gradient + edge highlights + shadow + structural details
    • Projectiles/Effects: core glow + color gradient + trail suggestion + bright center
    • NEVER use bare rect(), circle(), polygon() for visible game objects
    • "Has a gradient" is NOT enough - premium sprites have 5+ visual layers
    • See visual-assets.md for the universal sprite layer checklist

12. Create Gradient Background: Flat backgrounds look cheap.

    • Use makeGradientBg() with palette colors
    • Add subtle stars/dots for depth
    • Consider parallax layers for side-scrollers

13. Add Idle Animations: Static objects feel dead.

    • Coins: addFloat() - gentle bobbing
    • Player: addBreathing() - subtle scale pulse
    • Enemies: combine breathing + slight movement
    • Pickups: addSpin() or glow pulse

14. Plan Particle Effects: Every interaction needs MULTIPLE feedback layers:

    • Positive events (collect, score, win): particle burst + floating text (+1, +100) + screen flash + UI reaction + small shake
    • Negative events (damage, death, lose): explosion particles + screen shake + color flash + UI feedback
    • Movement events (jump, dash, land, turn): directional particles + object deformation (squash/stretch/spin)
    • Ambient atmosphere: floating particles + twinkling/pulsing background elements
    • Projectiles/Actions: spawn flash + trail particles + impact burst
    • One effect is NOT enough - premium feedback stacks 3+ effects per action

15. Establish Z-Index Hierarchy: Proper layering adds depth.

    • Background: z(-100)
    • Platforms: z(0)
    • Pickups: z(10)
    • Enemies: z(20)
    • Player: z(30)
    • Particles: z(50)
    • HUD: z(100) + fixed()

Phase 2: Autonomous Loop (The "Work")

Repeat this cycle until the game is Playable and Polished:

1. Implement/Refine: Write game code.

   • Constraint: Use KAPLAY.js for 2D (default), Three.js only if 3D is explicitly needed.
   • Constraint: Single HTML file with CDN imports (no build step for player).
   • Constraint: Color Palette: Use a predefined palette from visual-assets.md (PASTEL, PICO8, ENDESGA, NEON).
   • Constraint: No Bare Primitives: NEVER use rect(), circle(), polygon() for game objects. Use procedural sprites from visual-assets.md.
   • Constraint: Gradient Background: Always use makeGradientBg() instead of flat background color.
   • Constraint: Idle Animations: All game objects must have subtle animations (float, breathe, pulse, spin).
   • Constraint: Particle Effects: Every collision/pickup must spawn particles using burstParticles() or deathExplosion().
   • Constraint: Z-Index Layering: Use proper z-index hierarchy (BG:-100, platforms:0, pickups:10, enemies:20, player:30, particles:50, HUD:100).
   • Constraint: Game Loop: Use KAPLAY's onUpdate() for continuous logic. Never use noLoop().
   • Constraint: Input Handling: Use KAPLAY's onKeyPress, onKeyDown, isKeyDown.
   • Constraint: Collision: Use area() component and onCollide() for interactions.
   • Constraint: Canvas sizing: 800x600 or 16:9 aspect ratio.
   • Constraint: State Management: Use KAPLAY scenes for menu/play/gameover states.
   • Constraint: HUD: Use fixed() and z(100) for UI that ignores camera.
   • Constraint: Controls Display: Show control hints on screen at all times.
   • Constraint: Keyboard Handling: Use onKeyPress("space", ...) not raw DOM events for game input.

2. Playtest: Run node playtest.js

   • Captures screenshots at t=0, t=2s, t=5s
   • Simulates basic inputs (arrow keys, space, click)
   • Checks console for errors
   • Extracts game state variables if exposed

3. Critique:

   • Logs: Are there JavaScript errors?
   • Visual Audit: Open all generated screenshots (playtest-screenshots/) and evaluate:
     • Does it run?: Is there movement/change between frames?
     • Input Response: Did simulated input cause visible change?
     • Readability: Is text/HUD legible? Good contrast?
     • Composition: Is game area centered? Nothing cut off?
     • State Changes: Can you see game progressing (score changing, objects moving)?
   • Visual Quality Audit (CRITICAL - no sticks and boxes!):
     • No bare primitives?: Are all objects using procedural sprites with gradients/details?
     • Gradient background?: Is the background a gradient (not flat color)?
     • Objects alive?: Do coins bob, player breathe, objects animate?
     • Particles present?: Are there particle effects on interactions?
     • Color harmony?: Is a consistent palette used throughout?
     • Visual depth?: Are z-indexes creating proper layering?
     • Glow/highlights?: Do important objects (coins, player) have visual emphasis?
   • Gameplay Audit (mental simulation):
     • Is the core mechanic present and functional?
     • Is there a clear goal?
     • Is there a failure state?
     • Would a player understand what to do without external instructions?

4. Decide:

   • Errors? → Fix code → Repeat.
   • Static/Frozen? → Fix game loop, ensure onUpdate runs → Repeat.
   • No Input Response? → Fix input handlers, check key names → Repeat.
   • Missing Feedback? → Add juice (shake, flash, particles) → Repeat.
   • Unclear Goal? → Add visual indicators, HUD elements → Repeat.
   • No Win/Lose? → Implement end conditions → Repeat.
   • Unreadable Text? → Increase font size, add contrast → Repeat.
   • Bare rectangles/circles? → Replace with procedural sprites → Repeat.
   • Flat background? → Add gradient background → Repeat.
   • Static objects? → Add idle animations (float, breathe) → Repeat.
   • No particles? → Add burst/explosion effects → Repeat.
   • Playable, Clear, Responsive & Visually Polished? → Proceed to Phase 3.

Phase 3: Presentation (The "Launch")

Once the loop is complete and the game is polished:

1. Launch: Run npx vite --open.
2. Notify: Tell the user:
   • "Game is ready!"
   • "Controls: [List all controls]"
   • "Goal: [One sentence on how to win/play]"

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Technology Selection

Request Type	Framework	Template
2D game (default)	KAPLAY.js	templates/kaplay-2d.html
3D game (explicit)	Three.js	templates/threejs-3d.html
FPS / first-person shooter	Three.js	templates/threejs-fps.html
Ultra-simple (quiz, flashcard)	Vanilla Canvas	templates/canvas-minimal.html

Decision rule:

• Use KAPLAY for most 2D games (platformer, top-down, puzzle, etc.)
• Use threejs-fps.html for first-person shooters, DOOM-likes, or any game requiring pointer lock + mouse look
• Use threejs-3d.html for third-person 3D games, 3D puzzles, or non-shooter 3D experiences
• FPS indicators: "first-person", "FPS", "shooter", "DOOM", "Wolfenstein", "gun", "pointer lock"

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File References

• KAPLAY API: See references/kaplay-ref.md for component list and patterns
• Visual Assets: See references/visual-assets.md for procedural sprites, color palettes, animations, and particle effects
• Three.js API: See references/threejs-ref.md for 3D setup
• FPS Patterns: See references/fps-patterns.md for pointer lock, hit detection, enemy AI, weapon rendering
• Game Systems: See references/game-systems.md for difficulty scaling, scoring, persistence, UI patterns
• Game Patterns: See references/game-patterns.md for architecture (state machines, ECS, proc-gen)
• Physics Constants: See references/physics-constants.md for educational accuracy

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Common Pitfalls (Avoid These)

Gameplay Pitfalls

1. No game loop: Forgetting onUpdate() results in static screen
2. Wrong key names: Use "space" not "Space", "left" not "ArrowLeft" in KAPLAY
3. Missing area(): Objects won't collide without the area() component
4. Missing body(): Objects won't fall or respond to physics without body()
5. HUD moves with camera: Use fixed() component for UI elements
6. No scenes: Putting everything in global scope - use scene() for states
7. Forgetting go(): Must call go("sceneName") to start the first scene
8. Text too small: Default text size is often too small - use 20+ for HUD
9. No restart: Player stuck at game over - always add R to restart
10. Missing opacity() for lifespan(): The lifespan component requires opacity() to be present on the object
11. Unreachable goals: ALWAYS verify physics allow completing required actions. If player must reach X, calculate whether movement/jump/projectile range allows it.
12. Variable name rgb conflicts with KAPLAY: Never use const rgb = ... as it shadows KAPLAY's rgb() function. Use const c = hexToRgb(...) instead.

Visual Pitfalls (CRITICAL)

13. Bare primitives: Using rect(), circle(), polygon() for game objects looks terrible - use procedural sprites
14. Flat backgrounds: background: [r,g,b] looks cheap - use makeGradientBg() with texture/particles
15. Static objects: Game objects sitting motionless feel dead - add idle animations (addFloat(), addBreathing(), addSpin())
16. No particles: Interactions without visual feedback are unsatisfying - add particle bursts on all events
17. Random colors: Picking colors without a palette creates visual chaos - use PASTEL, PICO8, ENDESGA, or NEON
18. No z-index: Everything at same layer looks flat - use proper z-index hierarchy (-100 to 100)
19. No glow/outline: Important objects don't stand out - add glow/aura to key game objects
20. Bean for everything: loadBean() is a placeholder, not a finished sprite - create proper procedural sprites
21. "Good enough" sprites: A sprite with ONE gradient is functional, not premium. Premium = 5+ layers (glow + gradient + highlight + shadow + detail)
22. Single-effect feedback: One particle burst is weak. Premium = stacked effects (particles + text + flash + shake + UI reaction)
23. No movement deformation: Objects moving without squash/stretch/rotation feel stiff - add deformation on velocity changes
24. No impact particles: Collisions and surface contacts without particles lack weight - add particles on all physical interactions
25. No floating text: Score changes without visible "+N" text miss dopamine feedback - show value changes visually

FPS-Specific Pitfalls

26. Pointer lock not recovering: After alt-tab or focus loss, pointer lock is lost. ALWAYS re-request on focus/click events.
27. Enemies shoot through walls: Must check line of sight (step along ray) before allowing enemy attacks.
28. Enemies spawn in walls: Validate spawn positions against collision map; use fallback positions if invalid.
29. 3D hit detection for 2D gameplay: Classic FPS uses 2D XZ-plane distance with cone-of-fire, ignoring Y axis.
30. Weapon drawn sideways: FPS weapons should point forward (barrel vertical), not left-to-right like a side view.
31. No weapon feedback: Always add recoil animation (move down/up) and muzzle flash on fire.
32. Static enemy sprites: Animate walk (leg movement) and shoot (arms raised) states with canvas texture updates.
33. AI too aggressive: Balance detection range, attack rate, and damage. First-time playability > difficulty.
34. Score counts down during play: Live score should ONLY increase. Time bonuses calculated at end, only if mission succeeded.
35. Time bonus on failure: Speed bonus should only be awarded when the player wins, not on death.
36. Floating point stat display: Always use Math.floor() for health, armor, score display to avoid "99.7" health.
37. Modal UI not interactive: Game over screen must have proper pointer-events: auto and exit pointer lock.

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Known Warnings (Safe to Ignore)

• Puppeteer ARM64 warning: On Apple Silicon Macs, you may see a "Degraded performance warning" about Chrome/Rosetta. This is expected and does not affect playtest functionality.