Pygame Patterns Skill

Core Principles

1. Frame-Independent Movement: All movement uses delta_time for consistent speed regardless of framerate
2. Verified Patterns Only: All patterns come from working code in this project
3. Config-Driven: Use centralized config.py dataclasses, never hardcode values
4. Angle Conventions: 0° = right, 90° = up, 180° = left, 270° = down (pygame Y-axis is inverted)

Available Patterns

Projectiles

• Spawning projectiles at entity position with direction
• Frame-independent projectile movement (velocity vectors)
• Circle collision detection
• Lifetime management and despawning
• Converting angles to velocity vectors (accounting for pygame Y-axis)

Instructions

Step 1: Identify the Pattern Needed

• Projectile system: spawning, movement, collision → Use projectiles.md
• Entity movement: WASD, smooth rotation → See player.py:129-155
• Sprite loading: error handling, fallbacks → See utils.py:10-27
• Collision detection: circle-based → See game.py collision logic

Step 2: Reference the Pattern

Read .claude/skills/pygame-patterns/patterns/<pattern>.md

Read src/entities/<entity>.py

Step 3: Verify with Documentation

• Check pyproject.toml for pygame version
• Use ref_search_documentation for API verification
• Confirm function signatures and parameters

Step 4: Apply the Pattern

1. Add config dataclass to src/config.py (no hardcoded values)
2. Import necessary pygame modules
3. Use delta_time for frame-independent calculations
4. Add logging for entity lifecycle events
5. Follow angle conventions (0° = right, pygame Y-inverted)

Pattern Verification Checklist

• Read the pattern documentation
• Verify pygame APIs with ref.tools if using new functions
• Check that config values are in config.py
• Understand coordinate system (pygame Y-axis inverted)
• Test frame-independence (should work at any FPS)

Example Usage

1. Read the pattern:

   Read .claude/skills/pygame-patterns/patterns/projectiles.md

2. Follow the structure:
   • Create ProjectileConfig in config.py
   • Spawn at entity position with angle
   • Convert angle → velocity (cos/sin, negative Y)
   • Update position with delta_time
   • Check lifetime and collisions
3. Verify angle math:
   python

   # 0° = right, 90° = up (pygame Y is inverted)
   angle_rad = math.radians(angle)
   velocity_x = math.cos(angle_rad) * speed
   velocity_y = -math.sin(angle_rad) * speed  # negative for pygame

Integration with Other Skills

• python-testing: Use to generate tests for entity movement and collision
• entity-builder: Use this skill to inform entity generation patterns
• game-artist: Use patterns for sprite loading and rotation

Current Project Patterns

• Player rotation: src/entities/player.py:129-155 (smooth rotation, angle wrap)
• Sprite loading: src/utils.py:10-27 (error handling, fallbacks)
• Collision detection: Circle-based (used in player-zombie and player-powerup)
• Frame-independent movement: All entities use delta_time * speed

Quality Standards

• Be frame-independent (use delta_time)
• Use centralized config (no magic numbers)
• Include logging for entity events
• Handle pygame Y-axis inversion correctly
• Be verified from working code