#!ruby -Ks
# -*- mode: ruby; encoding: sjis -*-
# Last updated: <2014/06/25 06:50:55 +0900>

require 'dxruby'

font = Font.new(24)

imgs = Image.loadTiles("road_bg.png", 1, 480)
bgimg = Image.load("road_bg.png")

Window.bgcolor = [68, 97, 255]
mode = 0
bz = 0
start_y = 1

Window.loop do
  break if Input.keyPush?(K_ESCAPE)

  # Zキーで描画を変更
  mode = (mode + 1) % 6 if Input.keyPush?(K_Z)

  case mode
  when 0
    Window.draw(-320, 0, bgimg)
    Window.drawFont(4, 4, "BG全体を描画", font)

  when 1
    start_y.step(240-1, 1) { |y|
      i = y
      Window.draw(-320, y + 240, imgs[i])
    }
    Window.drawFont(4, 4, "上半分だけ描画", font)

  when 2
    start_y.step(240-1, 1) { |y|
      i = y + 240
      Window.draw(-320, y + 240, imgs[i])
    }
    Window.drawFont(4, 4, "下半分だけ描画", font)

  when 3
    start_y.step(240-1, 1) { |y|
      i = y + 240 * ((y / 16) & 0x01)
      Window.draw(-320, y + 240, imgs[i])
    }
    Window.drawFont(4, 4, "上と下を、ラスター単位で交互に描画 (一定間隔)", font)

  when 4
    sz = 320
    h = 240
    start_y.step(240-1, 1) { |y|
      z = (h * sz / y) # y座標毎のz値を求める
      i = y + 240 * ((z.to_i / 128) & 0x01)
      Window.draw(-320, y + 240, imgs[i])
    }
    Window.drawFont(4, 4, "上と下を、ラスター単位で交互に描画 (z値に基づく)", font)

  when 5
    sz = 320
    h = 240
    start_y.step(240-1, 1) { |y|
      z = (h * sz / y) + bz
      i = y + 240 * ((z.to_i / 128) & 0x01)
      Window.draw(-320, y + 240, imgs[i])
    }
    Window.drawFont(4, 4, "上と下を、ラスター単位で交互に描画 (z値を加算)", font)
    bz += 8
  end
end