DragonRuby Game Toolkit

This skill provides comprehensive guidance for building 2D games with DragonRuby Game Toolkit (DRGTK). Use for game loop implementation, sprite rendering, input handling, collision detection, animation, and scene management.

Quick Reference

Basic Game Structure

def boot args
  args.state = {}
end

def tick args
  # Called 60 times per second
  args.state.player ||= { x: 640, y: 360, w: 50, h: 50, path: 'player.png' }

  # Handle input
  args.state.player.x += 5 if args.inputs.right
  args.state.player.x -= 5 if args.inputs.left

  # Render
  args.outputs.sprites << args.state.player
end

Key Concepts

Concept	Purpose
def tick(args)	Main game loop (60 FPS)
args.outputs	Render sprites, labels, primitives
args.state	Persistent game data storage
args.inputs	Keyboard, mouse, controller input
args.grid	Screen dimensions (1280x720)
Geometry	Collision detection helpers

Coordinate System

• Screen: 1280x720 pixels
• Origin: Bottom-left (0, 0)
• Y-axis: Increases upward

(0, 720) ─────────────── (1280, 720)
    │                        │
    │     1280 × 720         │
    │                        │
(0, 0) ─────────────── (1280, 0)

Rendering Primitives

Use args.outputs.primitives for FIFO (first-in, first-out) render order control.

Sprites (Images)

args.outputs.primitives << {
  x: 100, y: 100, w: 64, h: 64,
  path: 'sprites/player.png',
  angle: 45,
  anchor_x: 0.5, anchor_y: 0.5,
  r: 255, g: 255, b: 255, a: 255,
  flip_horizontally: false
}

Labels (Text)

args.outputs.primitives << {
  x: 640, y: 360,
  text: "Score: #{args.state.score}",
  size_px: 22,
  anchor_x: 0.5, anchor_y: 0.5,
  r: 255, g: 255, b: 255
}

Solids and Borders

# Filled rectangle (use primitive_marker: :solid)
args.outputs.primitives << {
  x: 0, y: 0, w: 100, h: 100,
  r: 255, g: 0, b: 0,
  primitive_marker: :solid
}

# For many rectangles, use path: :solid for better performance
args.outputs.primitives << { x: 0, y: 0, w: 100, h: 100, path: :solid, r: 255, g: 0, b: 0 }

# Outline rectangle
args.outputs.primitives << { x: 0, y: 0, w: 100, h: 100, r: 0, g: 0, b: 0, primitive_marker: :border }

State Management

Use args.state with ||= for lazy initialization:

def tick args
  args.state.player ||= { x: 640, y: 360 }
  args.state.enemies ||= []
  args.state.score ||= 0
  args.state.scene ||= :title
end

Input Handling

Unified Input (Keyboard + Controller)

# Directional (arrows, WASD, gamepad)
args.inputs.up / down / left / right

# Magnitude values
args.inputs.left_right  # -1, 0, or 1
args.inputs.up_down     # -1, 0, or 1

Keyboard

args.inputs.keyboard.key_down.space   # Pressed this frame
args.inputs.keyboard.key_held.space   # Held down
args.inputs.keyboard.key_up.space     # Released this frame

Mouse

args.inputs.mouse.click               # Any button clicked
args.inputs.mouse.x / .y              # Position
args.inputs.mouse.inside_rect?(rect)  # Collision check

Collision Detection

if Geometry.intersect_rect?(player, enemy)
  enemy.dead = true
  args.state.score += 1
end

# Clean up dead entities
args.state.enemies.reject! { |e| e.dead }

Animation

# Frame-based animation
sprite_index = 0.frame_index(count: 6, hold_for: 8, repeat: true)
args.state.player.path = "sprites/player-#{sprite_index}.png"

Scene Management

def tick args
  args.state.scene ||= :title
  send("#{args.state.scene}_tick", args)
end

def title_tick args
  args.outputs.labels << { x: 640, y: 400, text: "Press SPACE", anchor_x: 0.5 }
  args.state.scene = :gameplay if args.inputs.keyboard.key_down.space
end

def gameplay_tick args
  # Game logic here
end

Best Practices

Do

• Use hash syntax for sprites/labels (clearer than arrays)
• Use ||= for state initialization
• Remove offscreen entities to prevent memory leaks
• Update logic before rendering
• Use $gtk.reset during development to reset state
• Use args.outputs.primitives for FIFO render order control
• Use primitive_marker: :solid or :border for rectangle types

Don't

• Hardcode magic numbers (use constants like FPS = 60)
• Forget early returns in scene methods
• Render before updating state (causes 1-frame lag)
• Let collections grow infinitely (reject dead entities)

Additional Resources

Reference Files

For detailed API documentation and patterns:

• references/core.md - Game loop, args object, rendering, coordinates
• references/input.md - Keyboard, mouse, controller input patterns
• references/entities.md - Entity spawning, collision, lifecycle
• references/game-logic/state.md - Timers, scoring, scene transitions
• references/game-logic/persistence.md - Save/load, file I/O patterns
• references/audio.md - Sound effects, music playback, audio controls
• references/rendering/primitives.md - Sprites, labels, solids, borders, layering
• references/rendering/animation.md - frame_index, spritesheets, easing functions

Example Files

Working code in examples/:

• examples/core/ - Hello world, sprites, labels, state, coordinates
• examples/input/ - Directional, keyboard, mouse, movement
• examples/entities/ - Storage, factories, collision, lifecycle
• examples/game-logic/ - Timers, scoring, save/load, state transitions
• examples/audio/ - Sound effects, background music, pause/resume
• examples/rendering/ - Sprites, labels, animation, layering

Development Workflow

def tick args
  # Game logic
end

$gtk.reset  # Add at end during development

Reset Methods

$gtk.reset            # Immediate reset
$gtk.reset_next_tick  # Reset before next tick (safer)

Debug Output

args.outputs.debug << "Frame: #{Kernel.tick_count}"
args.outputs.debug.watch args.state.player