Pew Pew: Writing Games with Ruby

Who am I?

Shawn Anderson

Hobbyist Game Dev

github.com/shawn42

shawn42@gmail.com

What are games?

fun interactions w/ sounds and graphics

They aren't easy

Game Loop

while game_running?
  # get user input
  # run AI
  # move everything
  # resolve collisions
  # draw graphics
  # play sounds
  # manage framerate
end

A better way

SDL

push those low-level bits

Rubygame

lets ruby talk to SDL

"John Croisant" jacius@gmail.com

rubygame.org

Gamebox

lets your brain talk to ruby

http://github.com/shawn42/gamebox

Create a Gamebox game

    $ gamebox omg_aliens
    $ cd omg_aliens
    $ rake

Setting the Stage

src/demo_stage.rb

class DemoStage < Stage
  def setup
    super
    @my_actor = create_actor :my_actor
    # ...

Setting the Stage

src/demo_stage.rb

target.fill [25,25,25,255]
for star in @stars
  target.draw_circle_s([star.x,star.y],1,[255,255,255,255])
end

Actors

src/my_actor.rb

class MyActor < Actor
end

Actor is just a location by default

ActorViews

src/my_actor.rb

class MyActorView < ActorView
  def draw(target, x_off, y_off)
    target.draw_box [actor.x,actor.y], [20,20], [240,45,45,255]
    # ...

ActorView doesn't exist by default

Behaviors

audible.rb (gamebox src)

require 'behavior'
class Audible < Behavior

  def setup
    @sound_manager = @actor.stage.sound_manager
    # ...

modifies an actor; mostly adds methods

Enough talk! Let's make something!

What should we build?

Step one: Rush mix tape

copy rushremix.ogg into omgaliens/data/music

soundmanager.playmusic :rush_remix in stage#setup

Create the player

$ ./script/generate actor Player

creates the actor and spec

answer

@player = spawn :player, :x => 200, :y => 550

Uncloak the Player

create an ActorView, nah

use canned :graphical behavior from Gamebox

copy player.png to data/graphics

answer

has_behavior :graphical

Undock the ship

use inputmanager.whilekey_pressed to monitor a key down

attr_accessor :move_left, :move_right
def setup
  i.while_key_pressed :left, self, :move_left
  i.while_key_pressed :right, self, :move_right

now to use those variables

add the :updatable behavior

define update(time) method that modifies position

has_behaviors :graphical, :updatable
def update(time_delta)
  velocity = 0.12 * time_delta 
  @x += velocity if @move_right
  @x -= velocity if @move_left
end

Player needs to shoot

$ ./script/generate actor FrickinLaser
$ ./script/generate view FrickinLaserView 

FrickinLaser needs to update its position

has_behavior :updatable

def update(time_delta)
  velocity = 4*0.1*time_delta
  @y -= velocity

  remove_self if @y < 30
end

FrickinLaserView needs to draw a box

def draw(target, x_offset, y_offset)

• target is a Rubygame screen
• xoffset, yoffset viewport offsets (ignore for now)

Draw it

target.draw_box_s([x,y], [x2,y2], color_array)

use the actor's x and y

color is RGBA array

Get a FrickinLaser on the Stage

Back to shooting ..

Player#setup should use input_manager#reg to shoot on KeyPressed, :space

Player#shoot should spawn :frickin_laser at player's location

Get the key press

input_manager.reg KeyPressed, :space do
  shoot
end

Shoot the FrickinLaser

def shoot
  laser = spawn :frickin_laser, 
    :x => @x + (image.width/2), :y => @y
end

What kind of silent laser is that?

copy shoot.wav into data/sounds

add :audible behavior to Player

play_sound takes the name of the file as a sym ##

has_behaviors :audible, :graph...
play_sound :shoot

Create Alien actor

Now let's shoot him!

Gamebox Collisions

circles only, for now

:collidable behavior (takes args)

:collidable => {:shape => :circle, 
    :radius => 20}

Add those behaviors

what to do when things collide?

use oncollisionof to define interactions

remove_self on alien and laser

play the :death sound

on_collision_of :alien, :frickin_laser do |alien,laser|
  alien.remove_self
  laser.remove_self
  sound_manager.play_sound :death
end

Resources

rubygame.org

code.google.com/p/sfxr

http://github.com/shawn42/gamebox/blob/master/docs/getting_started.rdoc

shawn42@gmail.com