-- Shader test 03
-- raster scroll modoki

function love.load()
  love.graphics.setDefaultFilter("nearest", "nearest")
  scr_w, scr_h = 640, 480
  canvas = love.graphics.newCanvas(scr_w, scr_h)

  -- load image
  img = love.graphics.newImage("bg_1024x1024.png")

  -- make shader
  myshader = love.graphics.newShader(
    [[
      extern number ang;
      extern vec2 scrSize;
      extern vec2 r;
      extern vec2 curve;
      extern vec2 basePos;
      vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords ){
        number factor_x = radians(r.x * (screen_coords.x / scrSize.x));
        number factor_y = radians(r.y * (screen_coords.y / scrSize.y));
        vec2 uv = texture_coords;
        uv.x = mod(-basePos.x + uv.x - curve.x * sin(ang + factor_y), 1.0);
        uv.y = mod(-basePos.y + uv.y - curve.y * sin(ang + factor_x), 1.0);
        vec4 pixel = Texel(texture, uv);
        return pixel * color;
      }
    ]]
  )

  myshader:send("scrSize", {scr_w, scr_h})
  myshader:send("r", {360.0 * 1.5, 360.0 * 1.5})
  myshader:send("curve", {0.02, 0.02})
  myshader:send("basePos", {0.0, 0.0})
  angle = 0
  bx = 0
  by = 0
end

function love.update(dt)
  bx = (bx + (64 / scr_w) * dt) % 1.0
  by = (by + (64 / scr_h) * dt) % 1.0
  myshader:send("basePos", {bx, by})

  angle = (angle + 180 * dt) % 360.0
  myshader:send("ang", math.rad(angle))

  px = (scr_w - img:getWidth()) / 2
  py = (scr_h - img:getHeight()) / 2
end

function love.draw()
  love.graphics.setCanvas(canvas)
  love.graphics.clear(0, 0, 0, 255)

  love.graphics.setShader(myshader)

  love.graphics.setColor(255, 255, 255)
  love.graphics.draw(img, px, py)

  love.graphics.setShader()

  love.graphics.setCanvas()

  -- draw canvas to window
  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
  love.graphics.setColor(255, 255, 255)
  love.graphics.draw(canvas, scr_ofsx, scr_ofsy, 0, scr_scale, scr_scale)

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

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