Unusual behavior of collision detection using Chingu

Question

I'm trying various ways of colliding the player with an item:

Coin.each_bounding_circle_collision(@player) do |coin, player|
    puts "coin collides with player"
end

Item.each_bounding_circle_collision(@player) do |item, player|
    puts "item collides with player"
end

@player.each_bounding_circle_collision(Item) do |player, item|
    puts "player collides with item"
end

@player.each_bounding_circle_collision(Coin) do |player, coin|
    puts "player collides with coin"
end

Of these, only the first and the last one works (i.e. the ones where I check against Coin), despite Item being the parent class of Coin:

class Item < Chingu::GameObject
    trait :timer
    trait :velocity
    trait :collision_detection
    trait :bounding_circle, :scale => 0.8

    attr_reader :score

    def initialize(options = {})
        super(options)

        self.zorder = Z::Item
    end
end

class Coin < Item
    def setup
        @animation = Chingu::Animation.new(:file => "media/coin.png", :delay => 100, :size => [14, 18])
        @image = @animation.first

        cache_bounding_circle
    end

    def update
        @image = @animation.next
    end
end

Due to my lowly knowledge of Ruby in general, I'm failing to see why this isn't working, maybe I'm missing something obvious. Any help would be greatly appreciated.

(Due to low reputation I can't tag this with 'chingu', so it's going under the next closest thing, 'libgosu')

Thanks.

(Source: Rubyroids)

score 3 · Accepted Answer · answered Nov 29 '11 at 16:01

3

Unfortunately, Chingu only keeps a record of all GameObject instances and GameObject instances by class, not by inheritance. What Chingu does here is checks collisions against Item.all, which is an array of purely Item instances, not its subclasses. The way to check all Item instances is:

@player.each_bounding_circle_collision(game_objects.of_class(Item)) do |player, item|
    puts "player collides with item"
end

Be aware, however, that that is quite slow, because game_objects#of_class goes through ALL game objects, picking out the ones that are kind_of? the class you want (same as Array#grep in newer Ruby version really, but presumably slower). You might want to record the list of Item instances every so often, not every time you want to check collisions, depending on how many objects you have in your game.

answered Nov 29 '11 at 16:01

Spooner

427
7
7

Is this something that changed recently? Many of the author of Chinga's old examples is using aforementioned techniques, but I noticed the collision detection in those examples is often broken as well. Thank you regardless, this will work for now. :) – jdlm Nov 29 '11 at 16:33
Yes, it used to work as you expect it to, but it changed at some point (It broke my games too, which is why I knew how to fix it :D). – Spooner Nov 29 '11 at 16:35
Ah, figured as much. Also your Wrath game has given me plenty of inspiration, so thanks for that. :) – jdlm Nov 29 '11 at 16:40

Unusual behavior of collision detection using Chingu

1 Answers1