dragonruby

This skill guides writing idiomatic, performant DragonRuby GTK (DRGTK) game code. DragonRuby uses a 60fps game loop, a bottom-left coordinate origin (1280×720), and flows everything through the args object passed to tick.

Sub-skills

For specialised topics, use these companion skills:

/dragonruby-rendering — render targets, cameras, HD/lowrez, pixel arrays, advanced sprites
/dragonruby-audio — spatial audio, procedural synthesis, beat sync, crossfading
/dragonruby-3d — 3D rendering, raycasting, Mode7, matrix math, VR
/dragonruby-pathfinding — A*, BFS, flood fill, quadtrees, spatial queries
/dragonruby-ui — UI controls, menus, scroll views, accessibility, input remapping
/dragonruby-platformer — platformer physics, action states, cameras, level editors

Project Structure

Each game gets its own unzipped copy of DragonRuby — never share the engine binary across projects.

mygame/
  app/
    main.rb       # entry point — defines tick(args)
    player.rb     # require from main.rb
    enemies.rb
  sprites/
  sounds/
  fonts/
  metadata/
    game_metadata.txt   # title, version, itch/steam IDs, orientation
    cvars.txt           # dev server, rendering options
  tmp/    # gitignore
  logs/   # gitignore

.gitignore

The DragonRuby engine binary is large and licensed per-developer — never commit it. Builds and runtime-generated directories should also be excluded.

# DragonRuby engine (download separately — do not commit)
dragonruby
dragonruby.exe
DragonRuby\ GTK.app/

# Runtime-generated directories
tmp/
logs/

# Export builds (large platform-specific archives)
builds/

# OS artifacts
.DS_Store
Thumbs.db

# Solargraph LSP config (optional — commit if whole team uses it)
# .solargraph.yml

Place this file at the root of your project (the directory containing mygame/). The engine binary lives at the same level and must not be pushed to a public repo due to licensing.

Core Loop & Lifecycle

def boot(args)
  args.state = {}   # initialize state cleanly
end

def tick(args)
  defaults(args)
  input(args)
  calc(args)
  render(args)
end

def shutdown(args)
  # runs before exit
end

Keep tick as a coordinator that delegates to focused methods. This is the idiomatic DRGTK structure.

State (`args.state`)

Persistent property bag — values survive between ticks. Use ||= to initialize once.

# Simple values
args.state.score     ||= 0
args.state.enemies   ||= []
args.state.game_over ||= false

# Entity with auto-generated id/timestamps
args.state.player ||= args.state.new_entity(:player) do |p|
  p.x = 640; p.y = 360; p.w = 32; p.h = 32
  p.hp = 3
end

# Spawning into a collection
args.state.enemies << args.state.new_entity(:enemy) do |e|
  e.x = rand(1280); e.y = 720; e.hp = 1
end

State entities auto-get: entity_id, entity_type, created_at, created_at_elapsed, global_created_at.

GTK.reset wipes all state. Within tick, use GTK.reset_next_tick.

Serialisation (save/load)

GTK.serialize_state('save.txt', args.state)
loaded = GTK.deserialize_state('save.txt')
args.state = loaded if loaded

For more control use JSON:

GTK.write_file('save.json', { score: args.state.score }.to_json)
data = GTK.parse_json(GTK.read_file('save.json'))

Class-based approach (for larger games)

class Game
  attr_gtk  # injects args, state, inputs, outputs, audio

  def tick
    state.player ||= { x: 640, y: 360 }
    calc_movement
    render_player
  end
end

$game ||= Game.new
def tick(args)
  $game.args = args
  $game.tick
end

Outputs / Rendering

Origin: bottom-left. Screen is 1280×720.

Render order (back → front): solids → sprites → primitives → labels → lines → borders → debug

Sprites

args.outputs.sprites << {
  x: 100, y: 100, w: 32, h: 32,
  path: 'sprites/hero.png',
  angle: 45,                          # degrees counter-clockwise
  anchor_x: 0.5, anchor_y: 0.5,      # rotation pivot (0–1)
  flip_horizontally: facing_left,
  r: 255, g: 255, b: 255, a: 255,    # tint + alpha
  # Sprite sheet cropping (source_ uses bottom-left origin):
  source_x: 0, source_y: 0, source_w: 16, source_h: 16
  # OR tile_ (top-left origin):
  # tile_x: 0, tile_y: 0, tile_w: 16, tile_h: 16
}

Triangle sprites (three-vertex form):

args.outputs.sprites << { x: 0, y: 0, x2: 50, y2: 100, x3: 100, y3: 0, path: 'sprites/tex.png' }

Convenience bang methods

rect.merge(r: 255, g: 0, b: 0).solid!    # returns hash with primitive_marker: :solid
rect.merge(r: 255).border!
rect.center.merge(text: "hi").label!

Solids, borders, lines

args.outputs.solids   << { x: 0, y: 0, w: 100, h: 100, r: 255, g: 0, b: 0, a: 200 }
args.outputs.borders  << { x: 10, y: 10, w: 200, h: 50, r: 255, g: 255, b: 0 }
args.outputs.lines    << { x: 0, y: 0, x2: 100, y2: 100, r: 255 }

Special paths:

{ path: :solid }    # filled rect without an image file
{ path: :empty }    # transparent (useful with blendmode: 0 for clipping)

Labels

args.outputs.labels << {
  x: 640, y: 360,
  text: "Score: #{args.state.score}",
  size_px: 24,                         # OR size_enum: 2
  alignment_enum: 1,                   # 0=left 1=center 2=right
  vertical_alignment_enum: 1,          # 0=bottom 1=center 2=top
  font: 'fonts/myfont.ttf',
  r: 255, g: 255, b: 255, a: 255
}

# Multi-line text helpers
lines = String.wrapped_lines(long_text, 40)    # array of strings, max 40 chars each

Background color

args.outputs.background_color = [30, 30, 40]

Debug output

args.outputs.debug << "tick: #{Kernel.tick_count}"
args.outputs.debug.watch(args.state.player)
args.outputs.debug << args.gtk.framerate_diagnostics_primitives

Primitives (manual layering)

args.outputs.primitives << { primitive_marker: :sprite, x: 0, y: 0, w: 32, h: 32, path: 'img.png' }

Inputs

Keyboard

args.inputs.keyboard.key_down.space     # true only the tick pressed
args.inputs.keyboard.key_held.left      # true while held
args.inputs.keyboard.key_up.escape      # true the tick released

# Available: .a–.z, .left, .right, .up, .down, .space, .enter,
#            .backspace, .escape, .tab, .shift, .control, .alt,
#            .f1–.f12, number keys, etc.

Mouse

args.inputs.mouse.x, args.inputs.mouse.y
args.inputs.mouse.click            # click event object (nil or has .x/.y/.point)
args.inputs.mouse.click.point      # {x:, y:} — useful for inside_rect?
args.inputs.mouse.button_left      # held
args.inputs.mouse.button_right
args.inputs.mouse.held             # any button held
args.inputs.mouse.up               # released this tick
args.inputs.mouse.moved
args.inputs.mouse.wheel            # { x:, y: } scroll delta
args.inputs.mouse.inside_rect?(rect)
args.inputs.mouse.position         # {x:, y:} — always available (no click required)

# Previous click for drag detection:
args.inputs.mouse.previous_click

Drag and drop pattern:

if args.inputs.mouse.click && target_under_mouse
  args.state.dragging = target_under_mouse.id
  args.state.drag_offset = { x: args.inputs.mouse.x - target.x,
                              y: args.inputs.mouse.y - target.y }
elsif args.inputs.mouse.held && args.state.dragging
  target.x = args.inputs.mouse.x - args.state.drag_offset.x
  target.y = args.inputs.mouse.y - args.state.drag_offset.y
elsif args.inputs.mouse.up
  args.state.dragging = nil
end

Controller

c = args.inputs.controller_one   # also controller_two, three, four
c.key_down.a; c.key_held.b; c.key_up.x
c.left_analog_x_perc    # -1.0 to 1.0
c.left_analog_y_perc
c.connected
# Buttons: .a .b .x .y .l1 .r1 .l2 .r2 .l3 .r3 .start .select

Unified input (keyboard + controller)

args.inputs.left_right           # -1, 0, or 1
args.inputs.up_down              # -1, 0, or 1
args.inputs.left_right_perc      # -1.0 to 1.0
args.inputs.directional_vector   # {x:, y:} or nil — safe-navigate with &.
args.inputs.last_active          # :keyboard, :mouse, or :controller

Unified movement:

v = args.inputs.directional_vector
player.x += (v&.x || 0) * player_speed
player.y += (v&.y || 0) * player_speed

Touch

args.inputs.touch               # hash of active touch points
args.inputs.finger_left.x
args.inputs.finger_right.x

Scene Management

def tick(args)
  args.state.scene ||= :title

  case args.state.scene
  when :title then tick_title(args)
  when :game  then tick_game(args)
  when :over  then tick_over(args)
  end

  # Apply queued scene changes atomically at end of tick
  if args.state.next_scene
    args.state.scene = args.state.next_scene
    args.state.next_scene = nil
  end
end

Never set args.state.scene directly mid-tick; always use next_scene.

For fade transitions:

args.state.scene_at ||= Kernel.tick_count
a = 255 - (255 * args.state.scene_at.ease(30, :flip))
args.outputs.solids << { x: 0, y: 0, w: 1280, h: 720, r: 0, g: 0, b: 0, a: a }

Geometry

All methods via Geometry.* or args.geometry.*.

Collision

Geometry.intersect_rect?(a, b)
Geometry.intersect_rect?(a, b, tolerance)
Geometry.inside_rect?(inner, outer)
Geometry.find_intersect_rect(rect, array)         # first hit
Geometry.find_all_intersect_rect(rect, array)     # all hits
Geometry.find_collisions(rects)                   # full collision map

# On objects directly:
player.intersect_rect?(enemy)
array.any_intersect_rect?(player)

# Quad tree (many entities):
qt = Geometry.create_quad_tree(rects)
Geometry.find_all_intersect_rect_quad_tree(rect, qt)

# Circles:
Geometry.intersect_circle?(shape1, shape2)
Geometry.point_inside_circle?(point, center, radius)

Distance & Angles

Geometry.distance(a, b)
Geometry.distance_squared(a, b)   # faster for comparisons
Geometry.angle(from, to)          # degrees
Geometry.angle_from(to, from)
Geometry.angle_vec(degrees)       # { x:, y: } unit vector

Transforms

Geometry.rotate_point(point, degrees, pivot)
Geometry.scale_rect(rect, ratio)
Geometry.anchor_rect(rect, anchor_x, anchor_y)
Geometry.center_inside_rect(target, reference)
Geometry.rect_center_point(rect)
Geometry.rect_to_lines(rect)
# UI menu navigation:
Geometry.rect_navigate(rect, rects, left_right, up_down, wrap_x: false, wrap_y: false)

Rect helpers on objects

player.shift_rect(dx, dy)       # returns moved rect hash
player.center                   # { x:, y: }

Audio

# One-shot sound
args.outputs.sounds << 'sounds/coin.wav'
args.outputs.sounds << { path: 'sounds/hit.wav', gain: 0.5 }

# Persistent / looping
args.audio[:music] = {
  input: 'sounds/theme.ogg',
  looping: true,
  gain: 0.8,
  pitch: 1.0,
  paused: false,
  x: 0.0, y: 0.0, z: 0.0   # spatial: -1 to 1
}
args.audio.delete(:music)         # stop
args.audio.volume = 0.5           # global volume

# Inspect after loading:
args.audio[:music].playtime    # seconds elapsed
args.audio[:music].playlength  # total duration

For advanced audio (spatial, synthesis, beat sync, crossfading) → use /dragonruby-audio.

Easing & Animation

Numeric helpers

# Frame animation
frame = start_tick.frame_index(frame_count: 4, hold_each_frame_for: 8, repeat: true)
path  = "sprites/walk_#{frame}.png"

# Timing
start_tick.elapsed_time         # ticks since start_tick
start_tick.elapsed?(120)        # true if 120 ticks have passed

# Lerp & math
current_x = current_x.lerp(target_x, 0.1)
current_x = current_x.towards(target_x, 5)   # move by up to 5 units/tick
val.clamp(0, 100)
val.clamp_wrap(0, 100)
val.remap(0, 100, 0.0, 1.0)
angle.vector_x; angle.vector_y             # cos/sin components
angle.vector_x(distance); angle.vector_y(distance)   # scaled
2.seconds   # => 120 frames

# Simple ease on a tick:
perc = start_tick.ease(duration, :smooth_stop_quint)  # 0.0 to 1.0
x = x_start + (x_end - x_start) * perc

Easing module

perc = Easing.ease(start_tick, args.tick_count, duration, :smooth_stop_quint)
# Definitions: :identity, :flip, :quad, :cube, :quart, :quint,
#   :smooth_start_quad/cube/quart/quint, :smooth_stop_quad/cube/quart/quint

perc = Easing.smooth_stop(start_at: start_tick, end_at: start_tick + duration,
                           tick_count: args.tick_count, power: 3)
perc = Easing.spline(start_tick, args.tick_count, duration, [[0, 0.33, 0.66, 1.0]])

Particle / fade queue

args.state.particles ||= []
# Spawn:
args.state.particles << { x: x, y: y, w: 8, h: 8,
                            dx: angle.vector_x(3), dy: angle.vector_y(3),
                            a: 255, path: 'sprites/particle.png' }
# Update:
args.state.particles.each { |p| p.x += p.dx; p.y += p.dy; p.dx *= 0.95; p.a -= 8 }
args.state.particles.reject! { |p| p.a <= 0 }

Layout

12×24 grid in landscape. Returns pixel rects for responsive UI.

rect = Layout.rect(row: 0, col: 0, w: 6, h: 2)
# => { x:, y:, w:, h:, center: { x:, y: } }

group = Layout.rect_group(row: 10, dcol: 1, w: 1, h: 1, group: items)
args.outputs.debug << Layout.debug_primitives  # visualise the grid
Layout.portrait?; Layout.landscape?

Runtime / GTK Utilities

Window & cursor

args.gtk.set_window_title("My Game")
args.gtk.toggle_window_fullscreen
args.gtk.set_window_scale(2)
args.gtk.hide_cursor
args.gtk.set_cursor('sprites/cursor.png', 0, 0)
args.gtk.set_mouse_grab(1)   # 0=ungrab, 1=grab, 2=grab+relative

File I/O (sandboxed)

args.gtk.write_file('save.json', content)
args.gtk.read_file('save.json')        # returns nil if missing
args.gtk.append_file('log.txt', "line\n")
args.gtk.delete_file('old.txt')
args.gtk.list_files('saves/')

Write path: macOS ~/Library/Application Support/[game], Windows AppData\Roaming\[dev]\[game], Linux ~/.local/share/[game].

Data parsing

args.gtk.parse_json('{"score":42}')
args.gtk.parse_json_file('data/config.json')
args.gtk.parse_xml_file('data/levels.xml')

Sprite utilities

args.gtk.calcstringbox("Hello", size_enum, font)   # [w, h]
args.gtk.calcspritebox('sprites/hero.png')          # [w, h]
args.gtk.get_string_rect("text", size_enum, font)   # hash
args.gtk.reset_sprite('sprites/hero.png')

Async HTTP

$req ||= args.gtk.http_get('https://example.com/data.json')
if $req && $req[:complete]
  data = args.gtk.parse_json($req[:response_data]) if $req[:http_response_code] == 200
  $req = nil
end

Development helpers

GTK.reset            # wipe state (use in console)
GTK.reset_next_tick  # safe to call within tick
GTK.slowmo!(2)       # half-speed debug
args.gtk.notify!("msg")
args.gtk.benchmark(seconds: 1, a: -> { fast }, b: -> { slow })
Kernel.tick_count           # current tick
Kernel.global_tick_count    # never resets
args.gtk.platform?(:macos)  # :win :linux :web :ios :android :touch :desktop
args.gtk.production?

Console (dev tool)

# In boot or tick:
GTK.console.set_command "reset_with count: 100"

# Custom console buttons:
class GTK::Console::Menu
  def custom_buttons
    [button(id: :my_btn, row: 2, col: 18, text: "Reset", method: :my_reset)]
  end
  def my_reset
    GTK.reset
  end
end

Array & Numeric Extensions

Array

tiles.map_2d { |row, col, tile| ... }
items.include_any?([:sword, :shield])
rects.any_intersect_rect?(player, 0.1)
list.reject_nil                    # compact alias
list.reject_false                  # removes nil + false
[1,2].product([3,4])               # all combinations
array.push_back(item)              # append
array.pop_front                    # shift

Numeric

2.seconds                    # 120 frames
val.lerp(10, 0.1)
val.towards(10, 2)           # move toward 10 by max 2
val.clamp(0, 100)
val.clamp_wrap(0, 100)
val.remap(0, 100, 0.0, 1.0)
val.to_radians; val.to_degrees
val.idiv(32)                 # integer division
val.fdiv(3)                  # float division
val.zmod?(3)                 # val % 3 == 0
tick.elapsed_time
tick.elapsed?(duration)
tick.frame_index(frame_count: 4, hold_each_frame_for: 8, repeat: true)
val.randomize(:ratio)        # random 0..val
val.randomize(:ratio, :sign) # random -val..val
(-1..1).rand                 # random float in range

Common Patterns

Spawn on interval

if Kernel.tick_count.zmod?(120)   # every 2 seconds
  args.state.enemies << { x: 1280, y: rand(720), w: 16, h: 16, hp: 3 }
end

Remove dead entities

args.state.enemies.reject! { |e| e[:hp] <= 0 || e[:x] < -32 }

Collision response

args.state.enemies.each do |e|
  next unless Geometry.intersect_rect?(args.state.player, e)
  e[:hp] -= 1
  # push-back:
  angle = Geometry.angle(e, args.state.player)
  e[:x] += angle.vector_x * 3
  e[:y] += angle.vector_y * 3
end

Snap to grid

grid_x = mouse_x.idiv(32) * 32
grid_y = mouse_y.idiv(32) * 32

Screen center

cx = args.grid.w / 2   # 640
cy = args.grid.h / 2   # 360

Smooth camera follow

args.state.cam_x = args.state.cam_x.lerp(player.x - 640, 0.08)
args.state.cam_y = args.state.cam_y.lerp(player.y - 360, 0.08)

Camera shake (trauma-based)

args.state.trauma = (args.state.trauma + 0.3).clamp(0, 1)
offset = 20.0 * args.state.trauma ** 2
cam.x_off = offset.randomize(:ratio, :sign)
cam.y_off = offset.randomize(:ratio, :sign)
args.state.trauma *= 0.92   # decay each tick

Timed flash effect

args.state.flash_at ||= -999
args.state.flash_at = Kernel.tick_count if hit
if args.state.flash_at.elapsed_time < 30
  a = 255 * args.state.flash_at.ease(30, :flip)
  args.outputs.solids << { x: 0, y: 0, w: 1280, h: 720, r: 255, g: 255, b: 255, a: a }
end

Floating damage numbers

args.state.floaters ||= []
args.state.floaters << { x: e.x, y: e.y, text: "-#{dmg}", a: 255, dy: 2 }
args.state.floaters.each { |f| f.y += f.dy; f.a -= 5 }
args.state.floaters.reject! { |f| f.a <= 0 }
args.outputs.labels << args.state.floaters.map { |f| f.merge(r: 255, g: 0, b: 0) }

Frame animation (sprite sheet)

col = args.state.anim_start.frame_index(frame_count: 6, hold_each_frame_for: 5, repeat: true)
args.outputs.sprites << { x: p.x, y: p.y, w: 32, h: 32,
                           path: 'sprites/run.png',
                           source_x: col * 32, source_y: 0, source_w: 32, source_h: 32 }

Directional sprite flipping

path: "sprites/hero.png",
flip_horizontally: player.dx < 0

Wave difficulty scaling

args.state.spawn_rate = (args.state.spawn_rate * 0.95).to_i.clamp(20, 300)

Seeded RNG for reproducibility

@rng = Random.new(seed)
val = @rng.rand(0...10)

Performance Tips

Prefer Hash or class primitives over Array form in hot code paths
args.outputs.static_sprites — holds references instead of clearing each tick; update in place
Implement draw_override(ffi_draw) + attr_sprite for maximum render throughput
Use Geometry.create_quad_tree for collision with many entities
Use Geometry.distance_squared instead of distance when comparing distances
Avoid allocating new arrays every tick — mutate in place (reject!, map!, push)
Use render targets (:symbol) to cache complex scenes; only redraw when content changes
Viewport culling: only transform/render entities inside the camera rect
One-time initialization guard: return if Kernel.tick_count != 0
args.gtk.warn_array_primitives! — audits array-form output usage

# Static sprites (fastest for large numbers of mostly-static objects)
if Kernel.tick_count == 0
  args.state.stars = 500.map { Star.new(args.grid) }
  args.outputs.static_sprites << args.state.stars
end
# Stars mutate in place; no need to re-add each tick

# draw_override (maximum speed):
class Star
  attr_sprite
  def draw_override(ffi_draw)
    ffi_draw.draw_sprite @x, @y, @w, @h, @path
  end
end