-- Shader test 08 raster 2

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

  img = love.graphics.newImage("cloud_1024x1024.png")
  -- img = love.graphics.newImage("scifi_bg_640x640.png")
  -- img = love.graphics.newImage("scifi_bg_640x640_blur.png")

  -- make shader
  local shadercode = [[
    extern number screen_distance;
    extern number floor_distance;
    extern number scroll_x;
    extern number scroll_y;
    extern number scroll_z;
    extern number upper_z_dir;

    const number z_limit = 6.0;

    vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords ) {
      float sx = screen_coords.x / love_ScreenSize.x - 0.5;
      float sy = screen_coords.y / love_ScreenSize.y - 0.5 - scroll_y;
      // float sx = texture_coords.x - 0.5;
      // float sy = texture_coords.y - 0.5 - scroll_y;

      float zv = (sy < 0.0)? upper_z_dir : 1.0;
      sy = abs(sy);
      // sy = max(sy, 0.0);

      float pz = (screen_distance * floor_distance) / sy;
      float px = sx * pz / screen_distance;
      texture_coords.x = mod(px + scroll_x, 1.0);
      texture_coords.y = mod(pz + scroll_z * zv, 1.0);
      vec4 texcolor = Texel(texture, texture_coords);
      texcolor.a *= (1.0 - step(z_limit, pz));
      return texcolor * color;
    }
  ]]
  myshader = love.graphics.newShader(shadercode)
  myshader:send("screen_distance", 0.7)
  myshader:send("floor_distance", 0.3)
  myshader:send("scroll_x", 0.0)
  myshader:send("scroll_y", 0.0)
  myshader:send("scroll_z", 0.0)
  myshader:send("upper_z_dir", 1.0)  -- upper half of the screen in z direction. 1.0 or -1.0

  v = 0.0
  px = (scr_w - img:getWidth()) / 2
  py = (scr_h - img:getHeight()) / 2
end

function love.update(dt)
  v = v + dt
  myshader:send("scroll_x", v * 1.2)
  myshader:send("scroll_z", v * -0.4)
end

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

  love.graphics.setColor(255, 255, 255)
  love.graphics.setShader(myshader)
  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_ox = (wdw_w - (scr_w * scr_scale)) / 2
  scr_oy = (wdw_h - (scr_h * scr_scale)) / 2
  love.graphics.setColor(255, 255, 255)
  love.graphics.draw(canvas, scr_ox, scr_oy, 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()
  elseif key == "f11" then
    -- toggle fullscreen
    if love.window.getFullscreen() then
      love.window.setFullscreen(false)
    else
      love.window.setFullscreen(true)
    end
  end
end