#!ruby -Ks
# -*- mode: ruby; encoding: sjis -*-
# Last updated: <2014/05/29 06:26:19 +0900>
#
# Xiaolin Wu's line algorithm - Rosetta Code
# http://rosettacode.org/wiki/Xiaolin%5FWu%27s%5Fline%5Falgorithm

require 'dxruby'

class XiaolinWuDraw

  def XiaolinWuDraw.draw_line(img, x1, y1, x2, y2, colour)
    if x1 == x2 and y1 == y2
      # not line. this is a dot.
      img[x1, y1] = colour
      return
    end

    dx, dy = x2 - x1, y2 - y1
    steep = (dy.abs > dx.abs)? true : false
    x1, y1, x2, y2, dx, dy = y1, x1, y2, x2, dy, dx if steep
    x1, y1, x2, y2 = x2, y2, x1, y1 if x1 > x2
    gradient = dy.to_f / dx.to_f

    # handle the first endpoint
    xend = x1.round
    yend = y1 + gradient * (xend - x1)
    fp = (x1 + 0.5) - (x1 + 0.5).truncate
    rfp = 1.0 - fp
    xgap = rfp
    xpxl1 = xend
    ypxl1 = yend.truncate
    fp = yend - yend.truncate
    rfp = 1.0 - fp
    XiaolinWuDraw.put_colour(img, xpxl1, ypxl1,     colour, steep, rfp * xgap)
    XiaolinWuDraw.put_colour(img, xpxl1, ypxl1 + 1, colour, steep,  fp * xgap)
    itery = yend + gradient

    # handle the second endpoint
    xend = x2.round
    yend = y2 + gradient * (xend - x2)
    fp = (x2 + 0.5) - (x2 + 0.5).truncate
    rfp = 1.0 - fp
    xgap = rfp
    xpxl2 = xend
    ypxl2 = yend.truncate
    fp = yend - yend.truncate
    rfp = 1.0 - fp
    XiaolinWuDraw.put_colour(img, xpxl2, ypxl2,     colour, steep, rfp * xgap)
    XiaolinWuDraw.put_colour(img, xpxl2, ypxl2 + 1, colour, steep,  fp * xgap)

    # in between
    (xpxl1 + 1).upto(xpxl2 - 1).each do |x|
      itt = itery.truncate
      fp = itery - itery.truncate
      rfp = 1.0 - fp
      XiaolinWuDraw.put_colour(img, x, itt,     colour, steep, rfp)
      XiaolinWuDraw.put_colour(img, x, itt + 1, colour, steep,  fp)
      itery = itery + gradient
    end
  end

  def XiaolinWuDraw.put_colour(img, x, y, col, steep, c)
    return if c == 0.0 or col[0] == 0
    x, y = y, x if steep
    o = img[x, y]
    n = Array.new(4)
    if o[0] >= 255
      # Bg Alpha = 255
      n[0] = 255
      for i in 1..3 do
        n[i] = (col[i] * c + o[i] * (1.0 - c)).round
      end
    elsif o[0] == 0
      # Bg Alpha = 0
      n[0] = (255 * c).round
      for i in 1..3 do
        n[i] = col[i]
      end
    else
      na = (255 * c).round
      n[0] = (na > o[0])? na : o[0]
      for i in 1..3 do
        n[i] = (col[i] * c + o[i] * (1.0 - c)).round
      end
    end
    img[x, y] = n
  end
end

# ----------------------------------------
# test

if $0 == __FILE__
  font = Font.new(14)

  w, h = 500, 500
  bgcol = [0, 0, 255] # blue (R,G,B)
  fgcol = [255, 255, 255, 0] # Yellow (A,R,G,B)
  fgcol2 = [255, 0, 255, 0] # Green (A,R,G,B)

  p = []
  10.step(460, 30) do |a|
    p.push([10, 10, 490, a, fgcol])
    p.push([10, 10, a, 490, fgcol])
  end
  p.push([10, 10, 490, 490, fgcol])

  img0 = Image.new(w, h)
  # img0.fill(bgcol)
  p.each do |d|
    x1, y1, x2, y2, col = d
    XiaolinWuDraw.draw_line(img0, x1, y1, x2, y2, col)
  end
  # img0.save("test.png")

  img1 = Image.new(w, h)
  p.each do |d|
    x1, y1, x2, y2, col = d
    img1.line(x1, y1, x2, y2, col)
  end

  img2 = Image.new(640, 480)

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

    # Push A key
    aa_enable = (Input.keyDown?(K_A))? false : true

    img2.clear
    x1, y1 = 320, 240
    x2, y2 = Input.mousePosX, Input.mousePosY

    if aa_enable
      XiaolinWuDraw.draw_line(img2, x1, y1, x2, y2, fgcol2)
      Window.draw(0, 0, img0)
      Window.draw(0, 0, img2)
    else
      img2.line(x1, y1, x2, y2, fgcol2)
      Window.draw(0, 0, img1)
      Window.draw(0, 0, img2)
    end

    s = "#{Window.real_fps} FPS  CPU: #{Window.getLoad.to_i} %"
    Window.drawFont(640 - 140, 2, s, font)
    s = "Push A key"
    Window.drawFont(640 - 140, 20, s, font)
  end
end