#!ruby -Ku
# -*- mode: ruby; coding: utf-8 -*-
# Last updated: <2017/04/06 21:07:42 +0900>
#
# Box-Muller法による正規乱数が作れそうかどうかをテスト

require 'dxruby'

# 乱数の結果を DXRuby の Image に描き込む
def get_image(w, h, data)
  # 最大カウント数を取得
  m = data.max

  # Imageに描き込み
  img = Image.new(w, h)
  w.times do |x|
    cnt = (data[x] * h.to_f / m).to_i
    y = h - 1
    cnt.times do
      img[x, y] = C_WHITE
      y -= 1
    end
  end
  return img
end

# Box-Muller法で乱数を取得
def get_box_mular(mu, sigma)
  x = rand
  y = rand
  r = Math.sqrt(-2.0 * Math.log(x)) * Math.cos(2.0 * Math::PI * y)
  return r * sigma + mu
end

w, h = 1280, 720
hh = h / 3
tc = 200000

# 一様分布になってるか確認
n = Array.new(w, 0)
tc.times do
  r = (rand * w).to_i
  n[r] += 1
end
nml_img = get_image(w, hh, n)

# Box-Muller法
n = Array.new(w, 0)
tc.times do
  rbm = get_box_mular(0.0, 1.0)
  r = (rbm * (w / 8) + (w / 2)).to_i
  n[r] += 1 if r >= 0 and r < w
end
bmr_img = get_image(w, hh, n)

# 乱数にコクを出すアレ
n = Array.new(w, 0)
tc.times do
  r = 0
  cnt = 4
  cnt.times { r += rand }
  r = ((r / cnt) * w).to_i
  n[r] += 1
end
kok_img = get_image(w, hh, n)

# 結果表示
Window.resize(w, h)
Window.loop do
  break if Input.keyPush?(K_ESCAPE)
  Window.draw(0, 0, nml_img)
  Window.draw(0, hh, bmr_img)
  Window.draw(0, hh + hh, kok_img)
end