-- Shader test 12 planet

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("grid_bg_480x480.png")
  img:setFilter("linear", "linear")

  -- make shader
  local shadercode = [[
    extern number start_x;
    extern number start_y;
    const float PI = 3.14159265;

    vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords ) {
      // float sx = (screen_coords.x - (love_ScreenSize.x / 2)) / love_ScreenSize.y;
      // float sy = (screen_coords.y - (love_ScreenSize.y / 2)) / love_ScreenSize.y;
      float tx = texture_coords.x - 0.5;
      float ty = texture_coords.y - 0.5;
      float a = asin(ty * 2);
      float v = a / PI;
      float r = cos(a);
      float b = asin(tx * 2 / r);
      float u = b / PI;
      texture_coords.x = mod((u + start_x) + 0.5, 1.0);
      texture_coords.y = mod((v + start_y) + 0.5, 1.0);
      vec4 texcolor = Texel(texture, texture_coords);
      texcolor.a = (tx * 2 > r)? 0.0 : texcolor.a;
      texcolor.a = (tx * 2 < -r)? 0.0 : texcolor.a;
      return texcolor * color;
    }
  ]]

  myshader = love.graphics.newShader(shadercode)
  myshader:send("start_x", 0.0)
  myshader:send("start_y", 0.0)

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

function love.update(dt)
  ang = ang + 0.1 * dt
  myshader:send("start_x", ang)
end

function love.draw()
  love.graphics.setCanvas(canvas)
  love.graphics.clear(24, 64, 176, 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