Game framework built on top of the opengl accelerated gamelib Gosu
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README.rdoc

CHINGU

github.com/ippa/chingu/tree/master

DOCUMENTATION: rdoc.info/projects/ippa/chingu

Ruby 1.9.1 is recommended. Should also work with 1.8.7+.

Chingu has started to settle down, thouch core classes and naming can still change for good reasons.

INSTALL

gem install chingu

DESCRIPTION

Game framework built on top of the OpenGL accelerated game lib Gosu. It adds simple yet powerful game states, prettier input handling, deployment safe asset-handling, a basic re-usable game object and automation of common task.

THE STORY

The last years I've dabbled around a lot with game development. I've developed games in both Rubygame and Gosu. I've looked at gamebox. Rubygame is a very capable framework with a lot of functionality (collision detection, very good event system etc). Gosu is way more minimalistic but also faster with OpenGL -acceleration. Gosu isn't likely to get much more complex since it does what it should do very well and fast.

After 10+ game prototypes and some finished smaller games I started to see patterns each time I started a new game. Making classes with x/y/image/other-parameters that I called update/draw on in the main loop. This became the basic Chingu::GameObject which encapsulates Gosus “Image.draw_rot” and enables automatic updating/drawing through “game_objects”.

There was always a huge big chunk of checking keyboard-events in the main loop. Borrowing ideas from Rubygame this has now become @player.keyboard(:left => :move_left, :space => :fire … etc.

CORE OVERVIEW

Chingu consists of the following core classes / concepts:

Chingu::Window

The main window, use it at you use Gosu::Window now. Calcs the framerate, takes care of states, handles chingu-formated input, updates and draws BasicGameObject / GameObjects automaticly. Available thoughout your source as $window (Yes, that's the only global Chingu has).

Chingu::GameObject

Use this for all your in game objects. The player, the enemies, the bullets, the powerups, the loot laying around. It's very reusable and doesn't contain any game-logic (that's up to you!). Only stuff to put it on screen a certain way. If you do GameObject.create() instead of new() Chingu will keep save the object in the “game_object”-list for automatic updates/draws. GameObjects also have the nicer Chingu input-mapping: @player.input = { :left => :move_left, :right => :move_right, :space => :fire} Has either Chingu::Window or a Chingu::GameState as “parent”.

Chingu::BasicGameObject

For those who think GameObject is a too little fat, there's BasicGameObject (GameObject inherits from BasicGameObject). BasicGameObject is just an empty frame (no x,y,image accessors or draw-logic) for you to build on. It can be extended with Chingus trait-system though. The new() vs create() behaivor of GameObject comes from BasicGameObject. BasicGameObject#parent points to either $window or a game state and is automaticly set on creation time.

Chingu::GameStateManager

Keeps track of the game states. Implements a stack-based system with push_game_state and pop_game_state.

Chingu::GameState

A “standalone game loop” that can be activated and deactivated to control game flow. A game state is very much like a main gosu window. You define update() and draw() in a gamestate. It comes with 2 extras that main window doesn't have. #setup (called when activated) and #finalize (called when deactivated)

If using game states, the flow of draw/update/button_up/button_down is: Chingu::Window –> Chingu::GameStateManager –> Chingu::GameState. For example, inside game state Menu you call push_game_state(Level). When Level exists, it will go back to Menu.

Traits

Traits are extensions (or plugins if you so will) to BasicGameObjects. The aim is so encapsulate common behaivor into modules for easy inclusion in your game classes. Making a trait is easy, just an ordinary module with the methods setup_trait(), update_trait() and/or draw_trait(). It currently has to be namespaced to Chingu::Traits for “has_trait” to work inside GameObject-classes.

OTHER CLASSES / HELPERS

Chingu::Text

Makes use of Gosu::Font more rubyish and powerful. In it's core, another Chingu::GameObject + Gosu::Font.

Chingu::Animation

Load and interact with tile-based animations. loop, bounce and access invidual frame(s) easily. An “@image = @animation.next!” in your Player#update is usually enough to get you started!

Chingu::Parallax

A class for easy paralaxxscrolling. See example3.rb for more.

Various Helpers

Both $window and game states gets some new graphical helpers, currently only 3, but quite useful:

fill()          # Fills whole window with color 'color'.
fill_rect()     # Fills a given Rect 'rect' with Color 'color'
fill_gradient() # Fills window or a given rect with a gradient between two colors.

If you base your models on GameObject (or BasicGameObject) you get:

Enemy.all                 # Returns an Array of all Enemy-instances
Enemy.size                # Returns the amount of Enemy-instances
Enemy.destroy_all         # Destroys all Enemy-instances
Enemy.destroy_if(&block)  # Destroy all objects for which &block returns true

BASICS / EXAMPLES

Chingu::Window

With Gosu the main window inherits from Gosu::Window. In Chingu we use Chingu::Window. It's a basic Gosu::Window with extra cheese on top of it. keyboard handling, automatic update/draw calls to all gameobjects, fps counting etc.

You're probably familiar with this very common Gosu pattern:

ROOT_PATH = File.dirname(File.expand_path(__FILE__))
class Game < Gosu::Window
  def initialize
    @player = Player.new
  end

  def update
    if button_down? Button::KbLeft
      @player.left
    elsif button_down? Button::KbRight
      @player.right
    end

    @player.update      
  end

  def draw
    @player.draw
  end
end

class Player
  attr_accessor :x,:y,:image
  def initialize(options)
    @x = options[:x]
    @y = options[:y]
    @image = Image.new(File.join(ROOT_PATH, "media", "player.png"))
  end

  def move_left
    @x -= 1
  end

  def move_right
    @x += 1
  end

  def draw
    @image.draw(@x,@y,100)
  end
end

Game.new.show   # Start the Game update/draw loop!

Chingu doesn't change any fundamental concept of Gosu, but it will make the above code cleaner:

#
# We use Chingu::Window instead of Gosu::Window
#
class Game < Chingu::Window
  def initialize
    super       # This is always needed if you want to take advantage of what chingu offers
    #
    # Player will automaticly be updated and drawn since it's a Chingu::GameObject
    # You'll need your own Game#update/#draw after a while, but just put #super there and Chingu can do its thing.
    #
    @player = Player.create
    @player.input = {:left => :move_left, :right => :move_right}
  end    
end

#
# If we create classes from Chingu::GameObject we get stuff for free.
# The accessors: image,x,y,zorder,angle,factor_x,factor_y,center_x,center_y,mode,update,draw
# You might recognize those from #draw_rot - http://www.libgosu.org/rdoc/classes/Gosu/Image.html#M000023
# And in it's core, that's what Chingu::GameObject is, an encapsulation of draw_rot with some extra cheese.
# For example, we get automatic calls to draw/update with Chingu::GameObject, which usually is what you want. 
# You could stop this by doing: @player = Player.new(:draw => false, :update => false)
#
class Player < Chingu::GameObject
  def initialize(options)
    super(options.merge(:image => Image["player.png"])
  end

  def move_left
    @x -= 1
  end

  def move_right
    @x += 1
  end    
end

Game.new.show   # Start the Game update/draw loop!

Roughly 50 lines became 26 more powerful lines. (you can do @player.angle = 100 for example)

If you've worked with Gosu for a while you're probably tired of passing around the window-parameter. Chingu solves this (as has many other developers) with a global variable $window. Yes, globals are bad, but in this case it kinda makes sense. It's used under the hood in various places.

Chingu::GameObject

This is our basic “game unit”-class, meaning most in game objects (players, enemies, bullets etc) should be inherited from Chingu::GameObject. The basic ideas behind it are:

  • Encapsulate only the very common basics that Most in game objects need

  • Keep naming close to Gosu, but add smart convenient methods / shortcuts and a more rubyish feeling

  • No game logic allowed in GameObject, since that's not likely to be useful for others.

I've chose to base it around Image#draw_rot. So basically all the arguments that you pass to draw_rot can be passed to GameObject#new when creating a new object, an example using almost all arguments would be:

#
# You probably recognize the arguments from http://www.libgosu.org/rdoc/classes/Gosu/Image.html#M000023
#
@player = Player.new(:image => Image["player.png"], :x=>100, :y=>100, :zorder=>100, :angle=>45, :factor_x=>10, :factor_y=>10, :center_x=>0, :center_y=>0)

#
# A shortcut for the above line would be
#
@player = Player.new(:image => Image["player.png"], :x=>100, :y=>100, :zorder=>100, :angle=>45, :factor=>10, :center=>0)

#
# I've tried doing sensible defaults:
# x/y = [middle of the screen]  for super quick display where it should be easy in sight)
# angle = 0                     (no angle by default)
# center_x/center_y = 0.5       (basically the center of the image will be drawn at x/y)
# factor_x/factor_y = 1         (no zoom by default)
# 
@player = Player.new

#
# By default Chingu::Window calls update & draw on all GameObjects in it's own update/draw.
# If this is not what you want, use :draw and :update
#
@player = Player.new(:draw => false, :update => false)

Input

One of the core things I wanted a more natural way of inputhandling. You can define input -> actions on Chingu::Window, Chingu::GameState and Chingu::GameObject. Like this:

#
# When left arrow is pressed, call @player.turn_left ... and so on.
#
@player.input = { :left => :turn_left, :right => :turn_right, :left => :halt_left, :right => :halt_right }

#
# In Gosu the equivalent would be:
#
def button_down(id)
  @player.turn_left		if id == Button::KbLeft
  @player.turn_right	if id == Button::KbRight
end

def button_up(id)
  @player.halt_left		if id == Button::KbLeft
  @player.halt_right	if id == Button::KbRight
end

Another more complex example:

#
# So what happens here?
#
# Pressing P would create an game state out of class Pause, cache it and activate it.
# Pressing ESC would call Play#close
# Holding down LEFT would call Play#move_left on every game iteration
# Holding down RIGHT would call Play#move_right on every game iteration
# Releasing SPACE would call Play#fire
#

class Play < Chingu::GameState
  def initialize
    self.input = { :p => Pause, 
                   :escape => :close, 
                   :holding_left => :move_left, 
                   :holding_right => :move_right, 
                   :released_space => :fire }
  end
end
class Pause < Chingu::GameState
  # pause logic here
end

In Gosu the above code would include code in button_up(), button_down() and a check for button_down?() in update().

Every symbol can be prefixed by either “released_” or “holding_” while no prefix at all defaults to pressed once.

So, why not :up_space or :release_space instead of :released_space? :up_space doesn't sound like english, :release_space sounds more like a command then an event.

Or :hold_left or :down_left instead of :holding_left? :holding_left sounds like something that's happening over a period of time, not a single trigger, which corresponds well to how it works.

And with the default :space => :something you would imagine that :something is called once. You press :space once, :something is executed once.

GameState / GameStateManager

Chingu incorporates a basic push/pop game state system (as discussed here: www.gamedev.net/community/forums/topic.asp?topic_id=477320).

Game states is a way of organizing your intros, menus, levels.

Game states aren't complicated. In Chingu a GameState is a class that behaves mostly like your default Gosu::Window (or in our case Chingu::Window) game loop.

# A simple GameState-example
class Intro < Chingu::GameState

  def update
    # game logic here
  end

  def draw
    # screen manipulation here
  end

  # Called when we enter the game state
  def setup
    @player.angle = 0   # point player upwards
  end

  # Called when we leave the game state
  def finalize
    push_game_state(Menu)   # switch to game state "Menu"
  end

end

Looks familiar yet? You can activate the above game state in 2 ways

class Game < Chingu::Window
  def initialize
    #
    # 1) Create a new Intro-object and activate it (pushing to the top).
    # This version makes more sense if you want to pass parameters to the gamestate, for example:
    # push_game_state(Level.new(:level_nr => 10))
    #
    push_game_state(Intro.new)

    #
    # 2) This leaves the actual object-creation to the game state manager.
    # Intro#initialize() is called, then Intro#setup()
    #
    push_game_state(Intro)
  end
end

Another example:

class Game < Chingu::Window
  def initialize
    #
    # We start by pushing Menu to the game state stack, making it active as the only state on stack.
    # :setup => :false which will skip setup() from being called (standard when switching to a new state)
    #
    push_game_state(Menu, :setup => false)

    #
    # We push another game state to the stack, Play. We now have 2 states, which active being first / active.
    #
    # :finalize => false will skip setup() from being called on game state 
    # that's being pushed down the stack, in this case Intro.setup().
    #
    push_game_state(Play, :finalize => false)

    #
    # This would remove Play state from the stack, going back to the Menu-state. But also:
    # .. skipping the standard call to Menu#setup     (the new game state)
    # .. skipping the standard call to Play#finalize  (the current game state)
    #
    # :setup => false can for example be useful when pop'ing a Pause game state. (see example4.rb)
    #
    pop_game_state(:setup => false, :finalize => :false)

    #
    # Replace the current game state with a new one.
    # :setup and :finalize options are available here as well.
    #
    switch_game_state(Credits)
  end
end

A GameState in Chingu is just a class with the following instance methods:

  • initialize() - called only once with push_game_state(Intro) but every time with push_game_state(Intro.new)

  • setup() - called each time the game state becomes active.

  • button_down(id) - Called when a button is down

  • button_up(id) - Called when a button is released

  • update() - just as in your normal game loop, put your game logic here.

  • draw() - just as in your normal game loop, put your screen manipulation here.

  • finalize() - called when a game state de-activated (for example by pushing a new one on top with push_game_state)

Chingu::Window automatically creates a @game_state_manager and makes it accessible in our game loop. By default the game loop calls update() / draw() on the the current game state.

Chingu also has a couple of helpers-methods for handling the game states: In a main loop or in a game state:

  • push_game_state(state) - adds a new gamestate on top of the stack, which then becomes the active one

  • pop_game_state - removes active gamestate and activates the previous one

  • switch_game_state(state) - replaces current game state with a new one

  • current_game_state - returns the current game state

  • previous_game_state - returns the previous game state (useful for pausing and dialog boxes, see example4.rb)

  • pop_until_game_state(state) - pop game states until given state is found

  • clear_game_states - removes all game states from stack

To switch to a certain gamestate with a keypress use Chingus input handler:

class Intro < Chingu::GameState
  def setup
    self.input = { :space => lambda{push_gamestate(Menu.new)} }
  end
end

Or Chingus shortcut:

class Intro < Chingu::GameState
  def setup
    self.input = { :space => Menu }
  end
end

Chingus inputhandler will detect that Menu is a gamestate-class, create a new instance, cache it and activate it with push_game_state().

Traits

Traits (often called behaivors) is a way of adding logic to any class inheriting from BasicGameObject / GameObject. Chingus trait-implementation is just ordinary ruby modules with 3 special methods:

- setup_trait 
- update_trait 
- draw_trait

Each of those 3 methods must call “super” to continue the trait-chain.

Example:

class Ogre < Chingu::GameObject
  has_trait :velocity, :timer

  def initialize(options)
    super
    @red = Gosu::Color.new(0xFFFF0000)
    @white = Gosu::Color.new(0xFFFFFFFF)

    #
    # some basic physics provided by the velocity-trait
    # These 2 parameters will affect @x and @y every game-iteration
    # So if your ogre is standing on the ground, make sure you cancel out the effect of @acceleration_y
    #
    @velocity_x = 1       # move constantly to the right
    @acceleration_y = 0.4 # gravity is basicly a downwards acceleration
  end

  def hit_by(object)
    #
    # during() and then() is provided by the timer-trait
    # flash red for 300 millisec when hit, then go back to normal
    #
    during(100) { @color = @red; @mode = :additive }.then { @color = @white; @mode = :default }
  end
end

The flow for a game object then becomes:

-- creating the object
1) GameObject#initialize(options)
2) GameObject#setup_trait(options)
-- each game iteration
3) GameObject#draw_trait
4) GameObject#draw
5) GameObject#update_trait
6) GameObject#update

There's a couple of traits included as default in Chingu:

Trait “timer”

Adds timer functionallity to your game object

during(300) { @color = Color.new(0xFFFFFFFF) }   # forces @color to white every update for 300 ms
after(400) { self.destroy }                      # destroy object after 400 ms
between(1000,2000) { self.rotate(10) }           # starting after 1 second, call rotate(10) every update during 1 second

Trait “velocity”

Adds variables velocity_x, velocity_y, acceleration_x, acceleration_y, max_velocity to game object. They modify x, y as you would expect. *speed / angle will come*

(IN DEVELOPMENT) Trait “effect”

Adds ability to automaticly fade, rotate and scale game objects.

  • API isn't stabilized yet! *

(IN DEVELOPMENT) Trait “collision_detection”

Adds class and instance methods for basic collision detection.

# Class method example
# This will collide all Enemy-instances with all Bullet-instances using the attribute #radius from each object.
Enemy.each_radius_collision(Bullet) do |enemy, bullet|
end

# You can also use the instance methods. This will use the Rect bounding_box from @player and each EnemyRocket-object.
@player.each_bounding_box_collision(EnemyRocket) do |player, enemyrocket|
  player.die!
end
  • API isn't stabilized yet! *

(IN DEVELOPMENT) Trait “retrofy”

Providing easier handling of the “retrofy” effect (non-blurry zoom) Aims to help out when using zoom-factor to create a retrofeeling with big pixels. Provides screen_x and screen_y which takes the zoom into account Also provides new code for draw() which uses screen_x / screen_y instead of x / y

Assets / Paths

You might wonder why this is necessary in the straight Gosu example:

ROOT_PATH = File.dirname(File.expand_path(__FILE__))
@image = Image.new(File.join(ROOT_PATH, "media", "player.png"))

It enables you to start your game from any directory and it will still find your assets (pictures, samples, fonts etc..) correctly. For a local development version this might not be important, you're likely to start the game from the games root-dir. But as soon as you try to deploy (for example to windows with OCRA - github.com/larsch/ocra/tree/master) you'll run into trouble of you don't do it like that.

Chingu solves this problem behind the scenes for the most common assets. The 2 lines above can be replaced with:

Image["player.png"]

You also have:

Sound["shot.png"]
Song["intromusic.ogg"]

By default Image, Sound and Sound searches the current directory and directory “media”. Add your own searchpaths like this:

Gosu::Image.autoload_dirs << File.join($window.root, "gfx")
Gosu::Sound.autoload_dirs << File.join($window.root, "samples")

This will add pathtoyourgamegfx and pathtoyourgamesamples to Image and Sound.

Thanks to Jacious of rubygame-fame (rubygame.org/) for his named resource code powering this.

Tiles and fonts are trickier since they require extra parameters so you'll have to do those the ordinary way. You have $window.root (equivalent to ROOT_PATH above) for free though which points to the dir containing the game.

Text

Text is a class to give the use of Gosu::Font more rubyish feel and fit it better into Chingu.

# Pure Gosu

@font = Gosu::Font.new($window, "verdana", 30)
@font.draw("A Text", 200, 50, 55, 2.0)

# Chingu

@text = Chingu::Text.create(:text => "A Text", :x => 200, :y => 50, :zorder => 55, :factor_x => 2.0)
@text.draw

@text.draw is usually not needed as Text is a GameObject and therefore automaticly updated/drawn (it #create is used instead of #new) It's not only that the second example is readable by ppl now even familiar with Gosu, @text comes with a number of changeable properties, x,y,zorder,angle,factor_x,color,mode etc. Set a new x or angle or color and it will instantly update on screen.

MISC / FAQ

How do I access my main-window easily?

Chingu keeps a global variable, $window, which contains the Chingu::Window instance. Since Chingu::Window is just Gosu::Window + some cheese you can do your $window.button_down?, $window.draw_line() etc from anywhere. See www.libgosu.org/rdoc/classes/Gosu/Window.html for a full set of methods.

How did you decide on naming of methods / classes?

There's 1 zillion ways of naming stuff. As a general guideline I've tried to follow Gosus naming. If Gosu didn't have a good name for a certain thing/method I've checked Ruby itself and then Rails since alot of Ruby-devs are familiar with Rails. GameObject.all is naming straight from rails for example. Most stuff in GameObject follow the naming from Gosus Image#draw_rot.

TODO:

  • add :padding and :align => :topleft etc to class Text

  • (skip) rename Chingu::Window so 'include Chingu' and 'include Gosu' wont make Window collide

  • (done) BasicObject vs GameObject vs ScreenObject => Became BasicGameObject and GameObject

  • (50%) some kind of componentsystem for GameObject (which should be cleaned up)

  • (done) scale <–> growth parameter. See trait “effect”

  • (done) Enemy.all … instead of game_objects_of_type(Enemy) ? could this be cool / understandable?

  • (done) Don't call .update(time) with timeparameter, make time available thru other means when needed.

  • (10% done) debug screen / game state.. check out shawn24's elite irb sollution :)

  • (done) Complete the input-definitions with all possible inputs (keyboard, gamepad, mouse)!

  • (done) Complete input-stuff with released-states etc

  • (done) More gfx effects, for example: fade in/out to a specific color (black makes sense between levels).

  • (posted request on forums) Summon good proven community gosu snippets into Chingu

  • (done) Generate docs @ ippa.github.com- rdoc.info/projects/ippa/chingu !

  • (done) A good scene-manager to manage welcome screens, levels and game flow- GameStateManager / GameState !

  • (20% done) make a playable simple game in examples\ that really depends on game states

  • (done) Make a gem- first gem made on github

  • (done) Automate gemgenning rake-task even more

  • (done) More examples when effects are more complete

  • class ChipmunkObject

  • (done) class Actor/MovingActor with maybe a bit more logic then the basic GameObject.

  • (60% done) Spell check all docs, sloppy spelling turns ppl off. tnx jduff ;).

  • Tests

  • (done) Streamline fps / tick code

  • (done) Encapsulate Font.new / draw_rot with a “class Text < GameObject”

  • (10% done) Make it possible for ppl to use the parts of Chingu they like

  • (done) At least make GameStateManager really easy to use with pure Gosu / Document it!

  • (50% done) Get better at styling rdocs

  • (done) all �gamestate� ? �game state� ? it's “game state”

  • (skipping) intergrate MovieMaker - solve this with traits instead.

  • A more robust game state <-> game_object system to connect them together.

  • FIX example4: :p => Pause.new would Change the “inside_game_state” to Pause and make @player belong to Pause.

WHY?

  • Plain Gosu is very minimalistic, perfect to build some higher level logic on!

  • Deployment and asset handling should be simple

  • Managing game states/scenes (intros, menus, levels etc) should be simple

  • There are patterns in game development

OPINIONS

  • Less code is usually better

  • Hash arguments FTW. And it becomes even better in 1.9.

  • Don't separate too much from Gosus core-naming

CREDITS:

  • Jacius of Rubygame (For doing cool stuff that's well documented as re-usable). So far rect.rb and named_resource.rb is straight outta Rubygame.

  • Jduff for input / commits

  • Jlnr,Philymore,Shawn24,JamesKilton for constructive feedback/discussions

  • Ariel Pillet for codesuggestions and cleanups

  • Thanks to github.com/tarcieri for require_all code, good stuff

REQUIREMENTS:

  • Gosu latest version

  • Ruby 1.9.1+ or 1.8.7+

  • gem 'opengl' if you want to use Image#retrofy, not needed otherwise

  • gem 'texplay' for some bonus Image-pixel operations, not needed otherwise