mapnik/boost/gil/extension/toolbox/hsl.hpp

// Copyright 2007 Christian Henning.
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

/*************************************************************************************************/

#ifndef GIL_HSL_H
#define GIL_HSL_H

////////////////////////////////////////////////////////////////////////////////////////
/// \file
/// \brief Support for HSL color space
/// \author Christian Henning \n
////////////////////////////////////////////////////////////////////////////////////////

#include <boost/gil/gil_all.hpp>

namespace boost { namespace gil {

/// \addtogroup ColorNameModel
/// \{
namespace hsl_color_space
{
/// \brief Hue
struct hue_t {};    
/// \brief Saturation
struct saturation_t {};
/// \brief Lightness
struct lightness_t {}; 
}
/// \}

/// \ingroup ColorSpaceModel
typedef mpl::vector3< hsl_color_space::hue_t
                    , hsl_color_space::saturation_t
                    , hsl_color_space::lightness_t
                    > hsl_t;

/// \ingroup LayoutModel
typedef layout<hsl_t> hsl_layout_t;


GIL_DEFINE_ALL_TYPEDEFS( 32f, hsl );

/// \ingroup ColorConvert
/// \brief RGB to HSL
template <>
struct default_color_converter_impl< rgb_t, hsl_t >
{
   template <typename P1, typename P2>
   void operator()( const P1& src, P2& dst ) const
   {
      using namespace hsl_color_space;

      // only bits32f for hsl is supported
      bits32f temp_red   = channel_convert<bits32f>( get_color( src, red_t()   ));
      bits32f temp_green = channel_convert<bits32f>( get_color( src, green_t() ));
      bits32f temp_blue  = channel_convert<bits32f>( get_color( src, blue_t()  ));

      bits32f hue, saturation, lightness;

      bits32f min_color = std::min( temp_red, std::min( temp_green, temp_blue ));
      bits32f max_color = std::max( temp_red, std::max( temp_green, temp_blue ));

      if ( max_color - min_color < 0.001 )
      {
         // rgb color is gray

         hue        = 0.f;
         saturation = 0.f;

         // doesn't matter which rgb channel we use.
         lightness = temp_red;
      }
      else
      {

         bits32f diff = max_color - min_color;

         // lightness calculation

         lightness = ( min_color + max_color ) / 2.f;

         // saturation calculation

         if( lightness < 0.5f )
         {
            saturation = diff 
                       / ( min_color + max_color );
         }
         else
         {
            saturation = ( max_color - min_color ) 
                       / ( 2.f - diff );

         }

         // hue calculation
         if( std::abs( max_color - temp_red ) < 0.0001f )
         {
            // max_color is red
            hue = ( temp_green - temp_blue ) 
                / diff;

         }
         else if( std::abs( max_color - temp_green) < 0.0001f )
         {
            // max_color is green
            // 2.0 + (b - r) / (maxColor - minColor)
            hue = 2.f 
                + ( temp_blue - temp_red ) 
                / diff;

         }
         else
         {
             // max_color is blue
             // 4.0 + (r - g) /  (maxColor - minColor)
             hue = 4.f 
                 + ( temp_red - temp_green ) 
                 / diff;
         }

         hue /= 6.f;
         
         if( hue < 0.f )
         {
            hue += 1.f;
         }
      }

      get_color( dst,hue_t() )        = hue;
      get_color( dst,saturation_t() ) = saturation;
      get_color( dst,lightness_t() )  = lightness;
   }
};

/// \ingroup ColorConvert
/// \brief HSL to RGB
template <>
struct default_color_converter_impl<hsl_t,rgb_t>
{
   template <typename P1, typename P2>
   void operator()( const P1& src, P2& dst) const
   {
      using namespace hsl_color_space;

      bits32f red, green, blue;

      if( std::abs( get_color( src, saturation_t() )) < 0.0001  )
      {
         // If saturation is 0, the color is a shade of gray
         red   = get_color( src, lightness_t() );
         green = get_color( src, lightness_t() );
         blue  = get_color( src, lightness_t() );
      }
      else
      {
         float temp1, temp2;
         float tempr, tempg, tempb;

         //Set the temporary values
         if( get_color( src, lightness_t() ) < 0.5 ) 
         {
            temp2 = get_color( src, lightness_t() )
                  * ( 1.f + get_color( src, saturation_t() ) );
         }
         else
         {
            temp2 = ( get_color( src, lightness_t() ) + get_color( src, saturation_t() )) 
                  - ( get_color( src, lightness_t() ) * get_color( src, saturation_t() ));
         }

         temp1 = 2.f
               * get_color( src, lightness_t() ) 
               - temp2;

         tempr = get_color( src, hue_t() ) + 1.f / 3.f;    

         if( tempr > 1.f )
         {
            tempr--;
         }

         tempg = get_color( src, hue_t() );     
         tempb = get_color( src, hue_t() ) - 1.f / 3.f;

         if( tempb < 0.f )
         {
            tempb++;
         }

         //Red     
         if( tempr < 1.f / 6.f )
         {
            red = temp1 + ( temp2 - temp1 ) * 6.f * tempr;
         }
         else if( tempr < 0.5f )
         {
            red = temp2;
         }
         else if( tempr < 2.f / 3.f )
         {
            red = temp1 + (temp2 - temp1) 
                * (( 2.f / 3.f ) - tempr) * 6.f;
         }
         else
         {
            red = temp1;
         }

         //Green       
         if( tempg < 1.f / 6.f )
         {
            green = temp1 + ( temp2 - temp1 ) * 6.f * tempg;
         }
         else if( tempg < 0.5f )
         {
            green = temp2;
         }
         else if( tempg < 2.f / 3.f )
         {
            green = temp1 + ( temp2 - temp1 )
                  * (( 2.f / 3.f ) - tempg) * 6.f;
         }
         else
         {
            green = temp1;
         }

         //Blue    
         if( tempb < 1.f / 6.f )
         {
            blue = temp1 + (temp2 - temp1) * 6.f * tempb;
         }
         else if( tempb < 0.5f )
         {
            blue = temp2;
         }
         else if( tempb < 2.f / 3.f )
         {
            blue = temp1 + (temp2 - temp1) 
                 * (( 2.f / 3.f ) - tempb) * 6.f;
         }
         else
         {
            blue = temp1;
         }
      }

      get_color(dst,red_t())  =
         channel_convert<typename color_element_type< P2, red_t >::type>( red );
      get_color(dst,green_t())=
         channel_convert<typename color_element_type< P2, green_t >::type>( green );
      get_color(dst,blue_t()) =
         channel_convert<typename color_element_type< P2, blue_t >::type>( blue );
   }
};

} }  // namespace boost::gil

#endif // GIL_HSL_H