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Product Requirements Document: Comically Large Paintbrush Drawing Game

Project Overview

A multiplayer drawing game using giant physical paintbrushes as alternative controllers, camera-based position tracking, and projection mapping for an immersive, physical-digital play experience.

Tech Stack: Kaplay.js, Computer Vision (camera triangulation), Projection Mapping, MongoDB

Feature Checklist

1. Hardware & Physical Setup

Paintbrush Controllers

  • Design and build oversized paintbrush props (determine size/weight for playability)
  • Attach trackable markers/LEDs to paintbrush tips for camera detection
  • Ensure markers are distinguishable per player (color-coded or unique patterns)
  • Test durability and ergonomics for extended play sessions

Camera Tracking System

  • Set up minimum 2 cameras for triangulation (determine optimal placement)
  • Calibrate cameras for the play space dimensions
  • Implement marker/LED detection algorithm
  • Calculate 3D position from multiple camera feeds
  • Map 3D coordinates to 2D canvas/projection space
  • Handle occlusion edge cases (player blocking camera view)

Projection Mapping

  • Select and mount projector(s) for play surface
  • Calibrate projection to physical play area boundaries
  • Account for surface irregularities if projecting on non-flat surfaces
  • Ensure adequate brightness for venue lighting conditions

2. Core Game Engine (Kaplay.js)

Canvas & Rendering

  • Initialize Kaplay.js game instance
  • Set up canvas matching projection resolution
  • Implement drawing layer (persistent brush strokes)
  • Implement UI layer (scores, timers, prompts)
  • Target 60fps rendering performance

Input Processing

  • Parse incoming position data for each tracked paintbrush
  • Normalize coordinates to canvas space
  • Smooth input data to reduce jitter (moving average or Kalman filter)
  • Detect brush "lift" vs "press" state (Z-axis or pressure threshold)

Drawing Mechanics

  • Render brush strokes when paintbrush is in "drawing" state
  • Support variable brush sizes
  • Support multiple brush colors (per player or selectable)
  • Implement stroke smoothing/interpolation for fluid lines

3. Game Modes

Split Canvas

  • Randomized prompt.
  • One canvas, each brush can only draw on one side of the canvas.
  • Color/brush selection UI.
  • 3 minute timer.
  • Save image of drawing at the end to MongoDB.

4. Multiplayer System

Player Management

  • Support 2 simultaneous players
  • Player color/identifier assignment
  • Player ready-up system for game start

Session Management

  • Game lobby/waiting room state
  • Round progression logic
  • Return to lobby or play again options

5. User Interface

In-Game HUD

  • Player indicators (colors, names, scores)
  • Current prompt display
  • Round/game timer
  • Current brush color/size indicator per player
  • Brush size options and undo button

Menu Screens

  • Title/splash screen
  • Mode selection menu
  • Credits screen

Feedback & Polish

  • Visual feedback when brush enters drawing zone
  • Sound effects for drawing, round start/end, scoring
  • Background music (toggleable)
  • Particle effects or visual flair on special events

6. Technical Infrastructure

Communication Layer

  • Define message protocol (position, player ID, brush state)
  • Synchronize game state across all display outputs

Computer Vision Pipeline

  • Camera feed capture and processing
  • Marker detection and identification
  • Multi-camera coordinate fusion
  • Output position data stream to game server

Configuration & Calibration

  • Calibration mode for camera alignment
  • Calibration mode for projection mapping
  • Save/load calibration profiles
  • Runtime adjustment tools for fine-tuning

7. Testing & Quality

Functional Testing

  • Single player drawing accuracy test
  • Multi-player simultaneous tracking test
  • Game mode flow testing (start to finish)
  • Edge case handling (out of bounds, rapid movement)

Performance Testing

  • Long-session stability test (no memory leaks, crashes)

User Testing

  • Playtest with target audience
  • Gather feedback on physical controller comfort
  • Iterate on game rules based on play sessions

8. Documentation & Delivery

  • Setup guide for hardware installation
  • Calibration procedure documentation
  • Software installation and run instructions
  • Troubleshooting guide for common issues
  • Final presentation/demo materials

Success Criteria

  1. Tracking Accuracy: Brush position maps to projected canvas within ±1cm accuracy
  2. Latency: Input-to-display lag under 50ms
  3. Stability: System runs for 30+ minutes without crashes
  4. Playability: Users can intuitively draw recognizable shapes within first attempt
  5. Fun Factor: Playtesters rate enjoyment 4+/5 on average

Open Questions

  • What surface will the game be projected onto? (floor, wall, table)
  • Indoor or outdoor venue? (affects lighting and projection)
  • What is the play area size? (affects camera placement and resolution needs)
  • Budget for hardware (cameras, projectors, paintbrush materials)?
  • Will there be a prompt database, or generated on the fly?
  • Any accessibility considerations for players?

Timeline Milestones

Phase Deliverables
Phase 1 Hardware prototype, basic camera tracking working
Phase 2 Kaplay.js canvas rendering, tracking data integration
Phase 3 Core drawing mechanics, single player functional
Phase 4 Multiplayer support, game modes implemented
Phase 5 Polish, playtesting, bug fixes
Phase 6 Final demo, documentation complete