Module: Rubygame::Sprites::UpdateGroup

Defined in:
lib/rubygame/sprite.rb

Overview

UpdateGroup is a mix-in module that extends Group to allow it to “erase” (i.e. draw over with a background Surface) and re-draw each sprite in its new position. This eliminates the “trail” of images that sprites would otherwise leave as they move around.

UpdateGroup adds a new attribute, @dirty_rects, which is an Array storing all Rects which need to be updated, including the old positions of the sprites. This attribute is returned when UpdateGroup#draw is called, so that it can be used to update the parts of the Screen that have changed.

The general order of calls each frame should be:

  1. #undraw; clear the old positions of the sprites.

  2. #update; update the sprites to their new positions.

  3. #draw; draw the sprites in their new positions.

This module can extend either a class or an already-existing Group instance (either empty or with members) without any special preparation.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#dirty_rects ⇒ Object

Returns the value of attribute dirty_rects.



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# File 'lib/rubygame/sprite.rb', line 389

def dirty_rects
  @dirty_rects
end

Class Method Details

.extend_object(obj) ⇒ Object

Defines @dirty_rects when an existing object is extended.



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# File 'lib/rubygame/sprite.rb', line 392

def UpdateGroup.extend_object(obj)
  super
  obj.dirty_rects = []
end

Instance Method Details

#draw(dest) ⇒ Object

call-seq: draw(dest) -> Array

Draw every sprite on Surface dest. See Group#draw. Returns an Array of Rects representing the portions of dest which were affected by the last #undraw and this #draw.



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# File 'lib/rubygame/sprite.rb', line 408

def draw(dest)
  self.each { |sprite| 
    @dirty_rects.push( sprite.draw(dest) ) 
  }
  rects = @dirty_rects
  @dirty_rects = []
  return rects
end

#initialize ⇒ Object

Initialize the Group, calling super and defining @dirty_rects.



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# File 'lib/rubygame/sprite.rb', line 398

def initialize
  super
  @dirty_rects = []
end

#undraw(dest, background) ⇒ Object

Draw over part of dest with image data from the corresponding part of background. For best results, background should be at least as big as dest (or, rather, the part of dest that will ever be drawn over).



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# File 'lib/rubygame/sprite.rb', line 421

def undraw(dest,background)
  self.each { |sprite|
    @dirty_rects.push( sprite.undraw(dest, background) )
  }
end