-- Shader test 05 hsv
--
-- reference
-- Blog: Fast branchless RGB to HSV conversion in GLSL - Lol Engine
-- http://lolengine.net/blog/2013/07/27/rgb-to-hsv-in-glsl

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("hsvbar.png")

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

      vec3 rgb2hsv(vec3 c) {
        vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
        vec4 p = c.g < c.b ? vec4(c.bg, K.wz) : vec4(c.gb, K.xy);
        vec4 q = c.r < p.x ? vec4(p.xyw, c.r) : vec4(c.r, p.yzx);
        float d = q.x - min(q.w, q.y);
        float e = 1.0e-10;
        return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
      }

      vec3 hsv2rgb(vec3 c) {
          vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
          vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
          return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
      }

      vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords ){
        vec4 pixel = Texel(texture, texture_coords);
        vec3 hsv = rgb2hsv(pixel.rgb);
        hsv.x = mod(hsv.x + factor, 1.0);
        vec3 rgb = hsv2rgb(hsv);
        pixel.r = rgb.r;
        pixel.g = rgb.g;
        pixel.b = rgb.b;
        return pixel * color;
      }
    ]]
  )
  factor = 0.0
  angle = 0
end

function love.update(dt)
  factor = factor + 0.25 * dt
  myshader:send("factor", factor)  -- 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