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/*******************************************************************************
* subsurface.h
*
* This module contains all defines, typedefs, and prototypes for subsurface.cpp.
*
* Author: Christoph Lipka
*
* ---------------------------------------------------------------------------
* Persistence of Vision Ray Tracer ('POV-Ray') version 3.7.
* Copyright 1991-2013 Persistence of Vision Raytracer Pty. Ltd.
*
* POV-Ray is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* POV-Ray is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
* ---------------------------------------------------------------------------
* POV-Ray is based on the popular DKB raytracer version 2.12.
* DKBTrace was originally written by David K. Buck.
* DKBTrace Ver 2.0-2.12 were written by David K. Buck & Aaron A. Collins.
* ---------------------------------------------------------------------------
* $File: //depot/public/povray/3.x/source/backend/lighting/subsurface.h $
* $Revision: #1 $
* $Change: 6069 $
* $DateTime: 2013/11/06 11:59:40 $
* $Author: chrisc $
*******************************************************************************/
#ifndef SUBSURFACE_H
#define SUBSURFACE_H
#include <boost/version.hpp>
#if BOOST_VERSION >= 103800 // flyweight is unavailable prior to boost 1.38
#define HAVE_BOOST_FLYWEIGHT 1
#else
#define HAVE_BOOST_FLYWEIGHT 0
#endif
#if HAVE_BOOST_FLYWEIGHT
#include <boost/flyweight.hpp>
#include <boost/flyweight/key_value.hpp>
#endif // HAVE_BOOST_FLYWEIGHT
namespace pov
{
//using namespace pov_base;
#if HAVE_BOOST_FLYWEIGHT
using boost::flyweights::flyweight;
using boost::flyweights::key_value;
#endif // HAVE_BOOST_FLYWEIGHT
/// Class storing SSLT data precomputed based on index of refraction.
class SubsurfaceInterior {
public:
SubsurfaceInterior(double ior);
DblRGBColour GetReducedAlbedo(const RGBColour& diffuseReflectance) const;
protected:
static const int ReducedAlbedoSamples = 100;
// precomputed reduced albedo for selected values of diffuse reflectance
struct PrecomputedReducedAlbedo {
float reducedAlbedo[ReducedAlbedoSamples+1];
PrecomputedReducedAlbedo(double ior);
double operator()(double diffuseReflectance) const;
};
#if HAVE_BOOST_FLYWEIGHT
flyweight<key_value<double,PrecomputedReducedAlbedo> > precomputedReducedAlbedo;
#else // HAVE_BOOST_FLYWEIGHT
// TODO - if flyweight is unavailable, we're currently resorting to a simple but memory-hungry fallback solution
PrecomputedReducedAlbedo precomputedReducedAlbedo;
#endif // HAVE_BOOST_FLYWEIGHT
};
/// Approximation to the Fresnel diffuse reflectance.
inline double FresnelDiffuseReflectance(double eta)
{
#if 0
// This is the original formula as per the 2001 Jensen et al. paper;
// however, this breaks down for large values of eta, or values < 1.0,
// and comes with some other bogosities.
return clip( -1.440/Sqr(eta) + 0.710/eta + 0.668 + 0.0636*eta, 0.0, 1.0-EPSILON );
#else
// My own approximation; maybe it's utterly wrong, but at least it is stable.
if (eta < 1.0)
return Sqr(eta)-pow(eta,2.25);
else
return ( (1.0-1.0/eta) + 3*pow(1.0-1.0/eta,4.5) ) / 4.0;
#endif
}
} // end of namespace
#endif // SUBSURFACE_H
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