diff --git a/.rubocop.yml b/.rubocop.yml
new file mode 100644
index 0000000..9024484
--- /dev/null
+++ b/.rubocop.yml
@@ -0,0 +1,21 @@
+# the extension popped up a warning to include this:
+AllCops:
+  NewCops: enable
+
+# my functions have too many assignments, I get it.
+# I have a lot to keep track of.
+Metrics/AbcSize:
+  Enabled: false
+# 10-line methods are /way/ too short
+Metrics/MethodLength:
+  Max: 100
+# Yeah, I've got constants with mutables in them. Doesn't bother me.
+Style/MutableConstant:
+  Enabled: false
+# I like my hash alignment neat.
+Layout/HashAlignment:
+  EnforcedHashRocketStyle: table
+  EnforcedColonStyle: table
+# DragonRuby required the file extension, therefore /not/ redundant.
+RedundantFileExtensionInRequire:
+  Enabled: false
\ No newline at end of file
diff --git a/app/main.rb b/app/main.rb
index 626b52a..8c4cd64 100644
--- a/app/main.rb
+++ b/app/main.rb
@@ -1,23 +1,33 @@
+# frozen_string_literal: true
+
+# first, third-party libraries
 require 'lib/coalesce.rb'
 
+# then, some basic classes required for lists of assets
+require 'app/sprite_instance.rb'
+
+# then, asset lists
+require 'sprites/_list.rb'
+
+# then, utility classes
 require 'app/input.rb'
 require 'app/sprite.rb'
 require 'app/util.rb'
+require 'app/sound.rb'
 
 require 'app/constants.rb'
 require 'app/menu.rb'
 require 'app/scene.rb'
 require 'app/game_setting.rb'
-require 'app/sound.rb'
 require 'app/text.rb'
 
+# then, the scenes
 require 'app/scenes/gameplay.rb'
 require 'app/scenes/main_menu.rb'
 require 'app/scenes/paused.rb'
 require 'app/scenes/settings.rb'
-
 require 'app/scenes/cube_tube.rb'
 
-# NOTE: add all requires above this
-
+# finally, the main tick
+# NOTE: add all other requires above this
 require 'app/tick.rb'
diff --git a/app/sprite.rb b/app/sprite.rb
index a2dccf3..4d6a1c7 100644
--- a/app/sprite.rb
+++ b/app/sprite.rb
@@ -1,95 +1,7 @@
+# frozen_string_literal: true
+
+# Module for managing and interacting with sprites.
 module Sprite
-  # Create type with ALL sprite properties AND primitive_marker
-  class SpriteInstance
-    attr_accessor :x, :y, :w, :h, :path, :angle, :a, :r, :g, :b,
-                  :source_x, :source_y, :source_w, :source_h,
-                  :tile_x, :tile_y, :tile_w, :tile_h,
-                  :flip_horizontally, :flip_vertically,
-                  :angle_anchor_x, :angle_anchor_y, :blendmode_enum
-
-    def primitive_marker
-      :sprite
-    end
-
-    def initialize opts
-      @x = opts[:x]
-      @y = opts[:y]
-      @w = opts[:w]
-      @h = opts[:h]
-      @path = opts[:path]
-      @angle = opts[:angle]
-      @a = opts[:a]
-      @r = opts[:r]
-      @g = opts[:g]
-      @b = opts[:b]
-      @source_x = opts[:source_x]
-      @source_y = opts[:source_y]
-      @source_w = opts[:source_w]
-      @source_h = opts[:source_h]
-      @tile_x = opts[:tile_x]
-      @tile_y = opts[:tile_y]
-      @tile_w = opts[:tile_w]
-      @tile_h = opts[:tile_h]
-      @flip_horizontally = opts[:flip_horizontally]
-      @flip_vertically = opts[:flip_vertically]
-      @angle_anchor_x = opts[:angle_anchor_x]
-      @angle_anchor_y = opts[:angle_anchor_y]
-      @blendmode_enum = opts[:blendmode_enum]
-    end
-
-    def render(args, opts = {})
-      args.outputs.sprites << [
-        opts[:x]._?(@x),
-        opts[:y]._?(@y),
-        opts[:w]._?(@w),
-        opts[:h]._?(@h),
-        opts[:path]._?(@path),
-        opts[:angle]._?(@angle),
-        opts[:a]._?(@a),
-        opts[:r]._?(@r),
-        opts[:g]._?(@g),
-        opts[:b]._?(@b),
-        opts[:source_x]._?(@source_x),
-        opts[:source_y]._?(@source_y),
-        opts[:source_w]._?(@source_w),
-        opts[:source_h]._?(@source_h),
-        opts[:tile_x]._?(@tile_x),
-        opts[:tile_y]._?(@tile_y),
-        opts[:tile_w]._?(@tile_w),
-        opts[:tile_h]._?(@tile_h),
-        opts[:flip_horizontally]._?(@flip_horizontally),
-        opts[:flip_vertically]._?(@flip_vertically),
-        opts[:angle_anchor_x]._?(@angle_anchor_x),
-        opts[:angle_anchor_y]._?(@angle_anchor_y),
-        opts[:blendmode_enum]._?(@blendmode_enum)
-      ]
-    end
-  end
-
-  # annoying to track but useful for reloading with +i+ in debug mode; would be
-  # nice to define a different way
-  SPRITES = {
-    train: SpriteInstance.new({ w: 1597, h: 540, path: 'sprites/train-1.png' }),
-    train_fore: SpriteInstance.new({ w: 1597, h: 540, path: 'sprites/train-2.png' }),
-    screen: SpriteInstance.new({ w: 250, h: 210, path: 'sprites/screen.png' }),
-    tunnel: SpriteInstance.new({ w: 267, h: 144, path: 'sprites/tunnel.png' }),
-    pause: SpriteInstance.new({ w: 16, h: 16, path: 'sprites/pause.png' }),
-    gray: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/gray.png' }),
-    black: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/black.png' }),
-    white: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/white.png' }),
-    red: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/red.png' }),
-    green: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/green.png' }),
-    blue: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/blue.png' }),
-    yellow: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/yellow.png' }),
-    indigo: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/indigo.png' }),
-    violet: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/violet.png' }),
-    orange: SpriteInstance.new({ w: 176, h: 148, path: 'sprites/box/orange.png' }),
-    screen_s1: SpriteInstance.new({ w: 250, h: 210, path: 'sprites/screen-s1.png' }),
-    screen_s2: SpriteInstance.new({ w: 250, h: 210, path: 'sprites/screen-s2.png' }),
-    screen_s3: SpriteInstance.new({ w: 250, h: 210, path: 'sprites/screen-s3.png' }),
-    screen_s4: SpriteInstance.new({ w: 250, h: 210, path: 'sprites/screen-s4.png' }),
-  }
-
   class << self
     def reset_all(args)
       SPRITES.each { |_, v| args.gtk.reset_sprite(v) }
@@ -99,5 +11,4 @@ module Sprite
       SPRITES.fetch(key)
     end
   end
-
-end
\ No newline at end of file
+end
diff --git a/app/sprite_instance.rb b/app/sprite_instance.rb
new file mode 100644
index 0000000..e55a366
--- /dev/null
+++ b/app/sprite_instance.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+# Create type with ALL sprite properties AND primitive_marker
+class SpriteInstance
+  attr_accessor :x, :y, :w, :h, :path, :angle, :a, :r, :g, :b,
+                :source_x, :source_y, :source_w, :source_h,
+                :tile_x, :tile_y, :tile_w, :tile_h,
+                :flip_horizontally, :flip_vertically,
+                :angle_anchor_x, :angle_anchor_y, :blendmode_enum
+
+  def primitive_marker
+    :sprite
+  end
+
+  def initialize(opts)
+    @x = opts[:x]
+    @y = opts[:y]
+    @w = opts[:w]
+    @h = opts[:h]
+    @path = opts[:path]
+    @angle = opts[:angle]
+    @a = opts[:a]
+    @r = opts[:r]
+    @g = opts[:g]
+    @b = opts[:b]
+    @source_x = opts[:source_x]
+    @source_y = opts[:source_y]
+    @source_w = opts[:source_w]
+    @source_h = opts[:source_h]
+    @tile_x = opts[:tile_x]
+    @tile_y = opts[:tile_y]
+    @tile_w = opts[:tile_w]
+    @tile_h = opts[:tile_h]
+    @flip_horizontally = opts[:flip_horizontally]
+    @flip_vertically = opts[:flip_vertically]
+    @angle_anchor_x = opts[:angle_anchor_x]
+    @angle_anchor_y = opts[:angle_anchor_y]
+    @blendmode_enum = opts[:blendmode_enum]
+  end
+
+  def render(args, opts = {})
+    args.outputs.sprites << [
+      opts[:x]._?(@x),
+      opts[:y]._?(@y),
+      opts[:w]._?(@w),
+      opts[:h]._?(@h),
+      opts[:path]._?(@path),
+      opts[:angle]._?(@angle),
+      opts[:a]._?(@a),
+      opts[:r]._?(@r),
+      opts[:g]._?(@g),
+      opts[:b]._?(@b),
+      opts[:source_x]._?(@source_x),
+      opts[:source_y]._?(@source_y),
+      opts[:source_w]._?(@source_w),
+      opts[:source_h]._?(@source_h),
+      opts[:tile_x]._?(@tile_x),
+      opts[:tile_y]._?(@tile_y),
+      opts[:tile_w]._?(@tile_w),
+      opts[:tile_h]._?(@tile_h),
+      opts[:flip_horizontally]._?(@flip_horizontally),
+      opts[:flip_vertically]._?(@flip_vertically),
+      opts[:angle_anchor_x]._?(@angle_anchor_x),
+      opts[:angle_anchor_y]._?(@angle_anchor_y),
+      opts[:blendmode_enum]._?(@blendmode_enum)
+    ]
+  end
+end
diff --git a/sprites/_list.rb b/sprites/_list.rb
new file mode 100644
index 0000000..12d3eae
--- /dev/null
+++ b/sprites/_list.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module Sprite
+  # annoying to track but useful for reloading with +i+ in debug mode; would be
+  # nice to define a different way
+  SPRITES = {
+    train:      SpriteInstance.new({ w: 1597, h: 540, path: 'sprites/train-1.png' }),
+    train_fore: SpriteInstance.new({ w: 1597, h: 540, path: 'sprites/train-2.png' }),
+    screen:     SpriteInstance.new({ w: 250,  h: 210, path: 'sprites/screen.png' }),
+    tunnel:     SpriteInstance.new({ w: 267,  h: 144, path: 'sprites/tunnel.png' }),
+    pause:      SpriteInstance.new({ w: 16,   h: 16,  path: 'sprites/pause.png' }),
+    gray:       SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/gray.png' }),
+    black:      SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/black.png' }),
+    white:      SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/white.png' }),
+    red:        SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/red.png' }),
+    green:      SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/green.png' }),
+    blue:       SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/blue.png' }),
+    yellow:     SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/yellow.png' }),
+    indigo:     SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/indigo.png' }),
+    violet:     SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/violet.png' }),
+    orange:     SpriteInstance.new({ w: 176,  h: 148, path: 'sprites/box/orange.png' }),
+    screen_s1:  SpriteInstance.new({ w: 250,  h: 210, path: 'sprites/screen-s1.png' }),
+    screen_s2:  SpriteInstance.new({ w: 250,  h: 210, path: 'sprites/screen-s2.png' }),
+    screen_s3:  SpriteInstance.new({ w: 250,  h: 210, path: 'sprites/screen-s3.png' }),
+    screen_s4:  SpriteInstance.new({ w: 250,  h: 210, path: 'sprites/screen-s4.png' }),
+  }
+end