agg/include/agg_gamma_lut.h

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2021-12-27 20:14:31 +01:00
//----------------------------------------------------------------------------
// 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