agg_gamma_lut.h

//----------------------------------------------------------------------------
// Anti-Grain Geometry - Version 2.4
// Copyright (C) 2002-2005 Maxim Shemanarev (http://www.antigrain.com)
//
// Permission to copy, use, modify, sell and distribute this software 
// is granted provided this copyright notice appears in all copies. 
// This software is provided "as is" without express or implied
// warranty, and with no claim as to its suitability for any purpose.
//
//----------------------------------------------------------------------------
// Contact: mcseem@antigrain.com
//          mcseemagg@yahoo.com
//          http://www.antigrain.com
//----------------------------------------------------------------------------

#ifndef AGG_GAMMA_LUT_INCLUDED
#define AGG_GAMMA_LUT_INCLUDED

#include <cmath>
#include "agg_basics.h"
#include "agg_gamma_functions.h"

namespace agg
{
    template<class LoResT=int8u, 
             class HiResT=int8u, 
             unsigned GammaShift=8, 
             unsigned HiResShift=8> class gamma_lut
    {
    public:
        typedef gamma_lut<LoResT, HiResT, GammaShift, HiResShift> self_type;

        enum gamma_scale_e
        {
            gamma_shift = GammaShift,
            gamma_size  = 1 << gamma_shift,
            gamma_mask  = gamma_size - 1
        };

        enum hi_res_scale_e
        {
            hi_res_shift = HiResShift,
            hi_res_size  = 1 << hi_res_shift,
            hi_res_mask  = hi_res_size - 1
        };

        ~gamma_lut()
        {
            pod_allocator<LoResT>::deallocate(m_inv_gamma, hi_res_size);
            pod_allocator<HiResT>::deallocate(m_dir_gamma, gamma_size);
        }

        gamma_lut() : 
            m_gamma(1.0), 
            m_dir_gamma(pod_allocator<HiResT>::allocate(gamma_size)),
            m_inv_gamma(pod_allocator<LoResT>::allocate(hi_res_size))
        {
            unsigned i;
            for(i = 0; i < gamma_size; i++)
            {
                m_dir_gamma[i] = HiResT(i << (hi_res_shift - gamma_shift));
            }

            for(i = 0; i < hi_res_size; i++)
            {
                m_inv_gamma[i] = LoResT(i >> (hi_res_shift - gamma_shift));
            }
        }

        gamma_lut(double g) :
            m_gamma(1.0), 
            m_dir_gamma(pod_allocator<HiResT>::allocate(gamma_size)),
            m_inv_gamma(pod_allocator<LoResT>::allocate(hi_res_size))
        {
            gamma(g);
        }

        void gamma(double g) 
        {
            m_gamma = g;

            unsigned i;
            for(i = 0; i < gamma_size; i++)
            {
                m_dir_gamma[i] = (HiResT)
                    uround(std::pow(i / double(gamma_mask), m_gamma) * double(hi_res_mask));
            }

            double inv_g = 1.0 / g;
            for(i = 0; i < hi_res_size; i++)
            {
                m_inv_gamma[i] = (LoResT)
                    uround(std::pow(i / double(hi_res_mask), inv_g) * double(gamma_mask));
            }
        }

        double gamma() const
        {
            return m_gamma;
        }

        HiResT dir(LoResT v) const 
        { 
            return m_dir_gamma[unsigned(v)]; 
        }

        LoResT inv(HiResT v) const 
        { 
            return m_inv_gamma[unsigned(v)];
        }

    private:
        gamma_lut(const self_type&);
        const self_type& operator = (const self_type&);

        double m_gamma;
        HiResT* m_dir_gamma;
        LoResT* m_inv_gamma;
    };

    //
    // sRGB support classes
    //

    // Optimized sRGB lookup table. The direct conversion (sRGB to linear) 
    // is a straightforward lookup. The inverse conversion (linear to sRGB) 
    // is implemented using binary search.
    template<class LinearType>
    class sRGB_lut_base
    {
    public:
        LinearType dir(int8u v) const
        {
            return m_dir_table[v];
        }

        int8u inv(LinearType v) const
        {
            // Unrolled binary search.
            int8u x = 0;
            if (v > m_inv_table[128]) x = 128;
            if (v > m_inv_table[x + 64]) x += 64;
            if (v > m_inv_table[x + 32]) x += 32;
            if (v > m_inv_table[x + 16]) x += 16;
            if (v > m_inv_table[x + 8]) x += 8;
            if (v > m_inv_table[x + 4]) x += 4;
            if (v > m_inv_table[x + 2]) x += 2;
            if (v > m_inv_table[x + 1]) x += 1;
            return x;
        }

    protected:
        LinearType m_dir_table[256];
        LinearType m_inv_table[256];

        // Only derived classes may instantiate.
        sRGB_lut_base() 
        {
        }
    };


    // sRGB_lut - implements sRGB conversion for the various types.
    // Base template is undefined, specializations are provided below.
    template<class LinearType>
    class sRGB_lut;

    template<>
    class sRGB_lut<float> : public sRGB_lut_base<float>
    {
    public:
        sRGB_lut()
        {
            // Generate lookup tables.
            m_dir_table[0] = 0;
            m_inv_table[0] = 0;
            for (unsigned i = 1; i <= 255; ++i)
            {
                // Floating-point RGB is in range [0,1].
                m_dir_table[i] = float(sRGB_to_linear(i / 255.0));
                m_inv_table[i] = float(sRGB_to_linear((i - 0.5) / 255.0));
            }
        }
    };

    template<>
    class sRGB_lut<int16u> : public sRGB_lut_base<int16u>
    {
    public:
        sRGB_lut()
        {
            // Generate lookup tables.
            m_dir_table[0] = 0;
            m_inv_table[0] = 0;
            for (int i = 1; i <= 255; ++i)
            {
                // 16-bit RGB is in range [0,65535].
                m_dir_table[i] = uround(65535.0 * sRGB_to_linear(i / 255.0));
                m_inv_table[i] = uround(65535.0 * sRGB_to_linear((i - 0.5) / 255.0));
            }
        }
    };

    template<>
    class sRGB_lut<int8u> : public sRGB_lut_base<int8u>
    {
    public:
        sRGB_lut()
        {
            // Generate lookup tables. 
            m_dir_table[0] = 0;
            m_inv_table[0] = 0;
            for (int i = 1; i <= 255; ++i)
            {
                // 8-bit RGB is handled with simple bidirectional lookup tables.
                m_dir_table[i] = uround(255.0 * sRGB_to_linear(i / 255.0));
                m_inv_table[i] = uround(255.0 * linear_to_sRGB(i / 255.0));
            }
        }

        int8u inv(int8u v) const
        {
            // In this case, the inverse transform is a simple lookup.
            return m_inv_table[v];
        }
    };

    // Common base class for sRGB_conv objects. Defines an internal 
    // sRGB_lut object so that users don't have to.
    template<class T>
    class sRGB_conv_base
    {
    public:
        static T rgb_from_sRGB(int8u x)
        {
            return lut.dir(x);
        }

        static int8u rgb_to_sRGB(T x)
        {
            return lut.inv(x);
        }

    private:
        static sRGB_lut<T> lut;
    };

    // Definition of sRGB_conv_base::lut. Due to the fact that this a template, 
    // we don't need to place the definition in a cpp file. Hurrah.
    template<class T>
    sRGB_lut<T> sRGB_conv_base<T>::lut;

    // Wrapper for sRGB-linear conversion. 
    // Base template is undefined, specializations are provided below.
    template<class T>
    class sRGB_conv;

    template<>
    class sRGB_conv<float> : public sRGB_conv_base<float>
    {
    public:
        static float alpha_from_sRGB(int8u x)
        {
            static const double y = 1 / 255.0;
            return float(x * y);
        }

        static int8u alpha_to_sRGB(float x)
        {
            if (x < 0) return 0;
            if (x > 1) return 255;
            return int8u(0.5 + x * 255);
        }
    };

    template<>
    class sRGB_conv<int16u> : public sRGB_conv_base<int16u>
    {
    public:
        static int16u alpha_from_sRGB(int8u x)
        {
            return (x << 8) | x;
        }

        static int8u alpha_to_sRGB(int16u x)
        {
            return x >> 8;
        }
    };

    template<>
    class sRGB_conv<int8u> : public sRGB_conv_base<int8u>
    {
    public:
        static int8u alpha_from_sRGB(int8u x)
        {
            return x;
        }

        static int8u alpha_to_sRGB(int8u x)
        {
            return x;
        }
    };
}

#endif