Gosu Basics - Developing Games With Ruby - page 16

5. Again, we are saving resources and not redrawing when there are no

@explosions in progress. needs_redraw? handles it.

It is important to understand that update and draw order is unpredictable, these methods
can be called by your system at different rate, you can't tell which one will be called more
often than the other one, so update should only be concerned with advancing object state,
and draw should only draw current state on screen if it is needed. The only reliable thing
here is time, consult Gosu.milliseconds to know how much time have passed.

Rule of the thumb: draw should be as lightweight as possible. Prepare all calculations in
update and you will have responsive, smooth graphics.

Music And Sound
Our previous program was clearly missing a soundtrack, so we will add one. A background
music will be looping, and each explosion will become audible.
01-hello/hello_sound.rb

1 require 'gosu'
2
3 def media_path (file)
4 File . join( File . dirname( File . dirname(

__FILE__ )), 'media' , file) 5

6 end
7
8 class Explosion
9 FRAME_DELAY = 10 # ms

SPRITE = media_path( 'explosion.png' ) 10

11
12 def self . load_animation (window)
13 Gosu :: Image . load_tiles(

window, SPRITE , 128 , 128 , false ) 14

15 end
16
17 def self . load_sound (window)
18 Gosu :: Sample . new(

window, media_path( 'explosion.mp3' )) 19

20 end
21
22 def initialize (animation, sound, x, y)
23 @animation = animation

sound . play 24

@x , @y = x, y 25