// with help of:
// JCL
// http://www.easyrgb.com/math.php?MATH=M19#text19
//
// 

//uniform sampler2D Texture1;

varying vec2 c; // texture coordinates from vertex shader
uniform sampler2D colorTex0;
uniform float AddHue;
uniform float AddSat;
uniform float AddLig;

float Hue_2_RGB(float v1, float v2, float vH )
{
	float ret;
   if ( vH < 0.0 )
     vH += 1.0;
   if ( vH > 1.0 )
     vH -= 1.0;
   if ( ( 6.0 * vH ) < 1.0 )
     ret = ( v1 + ( v2 - v1 ) * 6.0 * vH );
   else if ( ( 2.0 * vH ) < 1.0 )
     ret = ( v2 );
   else if ( ( 3.0 * vH ) < 2.0 )
     ret = ( v1 + ( v2 - v1 ) * ( ( 2.0 / 3.0 ) - vH ) * 6.0 );
   else
     ret = v1;
   return ret;
}

void main (void)
{
    vec4  color;

    float Cmax, Cmin;

    float D;
   
    float H, S, L;
    float R, G, B;

    // get fragment color
    color = texture2D(colorTex0, c);

    R = color.r;
    G = color.g;
    B = color.b;

// convert to HSL

    Cmax = max (R, max (G, B));
    Cmin = min (R, min (G, B));

// calculate lightness
    L = (Cmax + Cmin) / 2.0;

  if (Cmax == Cmin) // it's grey
  {
		H = 0.0; // it's actually undefined
		S = 0.0;
  }
  else
  {
    D = Cmax - Cmin; // we know D != 0 so we cas safely divide by it



// calculate Saturation
    if (L < 0.5)
    {
      S = D / (Cmax + Cmin);
    }
    else
    {
      S = D / (2.0 - (Cmax + Cmin));
    }

// calculate Hue
    if (R == Cmax)
    {
      H = (G - B) / D;
		} else {
      if (G == Cmax)
      {
      	 H = 2.0 + (B - R) /D;
      }
      else
      {
        H = 4.0 + (R - G) / D;
      }
   	}

    H = H / 6.0;


	}

// modify H/S/L values
H += AddHue;
S += AddSat;
L += AddLig;

if (H < 0.0)
{
	H = H + 1.0;
}

// clamp H,S and L to [0..1]

H = clamp(H, 0.0, 1.0);
S = clamp(S, 0.0, 1.0);
L = clamp(L, 0.0, 1.0);

// convert back to RGB

float var_2, var_1;

if (S == 0.0)
{
   R = L;
   G = L;
   B = L;
}
else
{
   if ( L < 0.5 )
   {
   var_2 = L * ( 1.0 + S );
   }
   else
   {
   var_2 = ( L + S ) - ( S * L );
   }

   var_1 = 2.0 * L - var_2;

   R = Hue_2_RGB( var_1, var_2, H + ( 1.0 / 3.0 ) );
   G = Hue_2_RGB( var_1, var_2, H );
   B = Hue_2_RGB( var_1, var_2, H - ( 1.0 / 3.0 ) );
}

 gl_FragColor = vec4(R,G,B, color.a);
	
}