-- Shader test 04
-- palette change 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("colorbar_circle01.png")

  -- make shader
  myshader = love.graphics.newShader(
    [[
      extern number factor;
      extern vec3 checkcolor;
      extern vec3 replacecolor;

      vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords ){
        vec4 pixel = Texel(texture, texture_coords);
        if (pixel.r == checkcolor.r && pixel.g == checkcolor.g && pixel.b == checkcolor.b) {
          pixel.r = pixel.r * (1.0 - factor) + replacecolor.r * factor;
          pixel.g = pixel.g * (1.0 - factor) + replacecolor.g * factor;
          pixel.b = pixel.b * (1.0 - factor) + replacecolor.b * factor;
        }
        return pixel * color;
      }
    ]]
  )

  myshader:send("checkcolor", {0.0, 1.0, 0.0})  -- R,G,B
  myshader:send("replacecolor", {0.0, 0.0, 0.0})  -- R,G,B
  angle = 0
end

function love.update(dt)
  angle = (angle + 90 * dt) % 360.0
  local v = 1.0 - math.abs(math.sin(math.rad(angle)))
  myshader:send("factor", v)  -- set 0.0 - 1.0

  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