-- Fake raster scroll

-- init
function love.load()

  -- set filter
  love.graphics.setDefaultFilter("nearest", "nearest")

  -- set canvas size
  scr_w, scr_h = 1280, 720
  canvas = love.graphics.newCanvas(scr_w, scr_h)

  -- get window width and height
  wdw_w, wdw_h = love.graphics.getDimensions()

  scr_scale = math.min((wdw_w / scr_w), (wdw_h / scr_h))
  scr_ofsx = (wdw_w - (scr_w * scr_scale)) / 2
  scr_ofsy = (wdw_h - (scr_h * scr_scale)) / 2

  -- load image
  img = love.graphics.newImage("bg1.png")
  img2 = love.graphics.newImage("bg2.png")

  -- make Quad (raster)
  imgs = {}
  bg_x_list = {}
  for i = 1, img:getHeight() do
    local x = 0
    local y = i - 1
    imgs[i] = love.graphics.newQuad(x, y, img:getWidth(), 1, img:getDimensions())
    bg_x_list[i] = 0
  end

  bg_x = 0
end

-- update
function love.update(dt)
  local w0 = 684
  local w1 = 1195

  local mx = love.mouse.getX()
  local d = mx - (scr_w / 2)
  
  bg_x = (bg_x + 2 * d * dt) % w0
  
  -- set bg_x_list
  local x0 = -bg_x
  local x1 = -bg_x * w1 / w0
  for i = 1, img:getHeight() do
    local y = i - 1
    bg_x_list[i] = x0 + y * (x1 - x0) / (img:getHeight() - 1)
  end
  
end

-- draw
function love.draw()
  -- set canvas
  love.graphics.setCanvas(canvas)

  -- fill BG color
  love.graphics.setColor(0, 0, 1.0)
  love.graphics.rectangle("fill", 0, 0, scr_w, scr_h)

  -- draw bg upper
  love.graphics.setColor(1.0, 1.0, 1.0)
  love.graphics.draw(img2, -bg_x, 0)

  -- draw raster
  local y = scr_h - img:getHeight()
  love.graphics.setColor(1.0, 1.0, 1.0)
  for i = 1, img:getHeight() do
    love.graphics.draw(img, imgs[i], bg_x_list[i], (y + i - 1))
  end

  -- unset canvas
  love.graphics.setCanvas()

  -- draw canvas to window
  love.graphics.setColor(1.0, 1.0, 1.0)
  love.graphics.draw(canvas, scr_ofsx, scr_ofsy, 0, scr_scale, scr_scale)

  -- print FPS
  love.graphics.print("FPS: "..tostring(love.timer.getFPS()), 10, 10)
end

function love.keypressed(key, isrepeat)
  -- ESC to exit
  if key == "escape" then
    love.event.quit()
  end
end