From: "F. Senault" <fred@...>
Date: 2011-05-09T16:50:30+09:00
Subject: Re: Index to coordinates conversion, according the matrix shape

Le 9 mai 2011 � 00:14, Paul A. a �crit :

> But how can we do the opposite? I mean, a method looking like:
> 
>     index_to_coordinates([3, 3], 3) # => [0, 1]

A small example from a project of mine.  Maybe you'll find things of
interest (the each method does that conversion, for instance).

class Grid
  include Enumerable

  attr_reader :width, :height, :depth
  def initialize(width, height, depth)
    @width = width
    @height = height
    @depth = depth
    @tiles = Array.new(width * height * depth)
  end

  def include?(x, y, z)
    (0..@width).include?(x) &&
    (0..@height).include?(y) &&
    (0..@depth).include?(z)
  end

  def [](x, y, z)
    if include? x, y, z
      @tiles[z * @width * @height + y * @width + x]
    else
      raise "Tile out of bound : (#{x}, #{y}, #{z}) - #{self}"
    end
  end

  def []=(x, y, z, v)
    if include? x, y, z
      @tiles[z * @width * @height + y * @width + x] = v
    else
      raise "Tile out of bound : (#{x}, #{y}, #{z}) - #{self}"
    end
  end

  def each
    @tiles.each_with_index do |v, i|
      yield v, 
            i % @width,              # x
            (i / @width) % @height,  # y
            i / (@height * @width)   # z
    end
  end

  def window(x, y, z, w, h, d)
    z.upto(z + d - 1) do |sz|
      y.upto(y + h - 1) do |sy|
        x.upto(x + w - 1) do |sx|
          yield self[sx, sy, sz], sx, sy, sz
        end
      end
    end
  end
end

Fred
-- 
No will to wake for this morn
To see another black rose born
Deathbed is slowly covered with snow
                                            (Nightwish, End of All Hope)