ibdf.h

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/*
    toxic - A Global Illumination Renderer
    Copyright (C) 2003-2004 Francois Beaune
    Contact: http://toxicengine.sourceforge.net/

    This file is part of toxic.

    toxic is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    toxic 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with toxic; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#ifndef TOXIC_RENDERER_IBDF_H
#define TOXIC_RENDERER_IBDF_H

#include "common/math/real.h"
#include "common/math/sampling.h"
#include "common/math/vector3.h"
#include "common/misc/iclonable.h"
#include "context.h"
#include "globals.h"

#include <cassert>

namespace toxic {

    //! Bidirectional Distribution Function (BDF).

    //! Incoming and outgoing directions are both always expressed in the upper
    //! part of the unit hemisphere, and they are always unit-length.

    class IBDF : public sheep::IClonable<IBDF> {
    public:
        virtual ~IBDF() {}

        virtual bool IsDiffuse() const { return true; }
        virtual bool IsSpecular() const { return false; }

        //! Evaluates the function. Both the incoming and outgoing directions are
        //! expressed in local space.
        virtual sheep::Real Evaluate(
            const Context &context,
            const sheep::Vector3 &incoming,
            const sheep::Vector3 &outgoing
        ) const = 0;

        virtual sheep::Real EvaluateSpecular(
            const Context &context,
            const sheep::Vector3 &incoming,
            sheep::Vector3 *outgoing
        ) const;

        //! Samples the function in order to obtain an outgoing direction, given
        //! an incoming direction. The probability with which the direction has
        //! been chosen is also computed. Both incoming and outgoing directions
        //! are expressed in local space.
        //! Note: this method must be overridden if the IsSpecular() method is
        //! defined to return true.
        virtual void Sample(
            const Context &context,
            const sheep::Vector3 &incoming,
            sheep::Vector3 *outgoing,
            sheep::Real *prob,
            sheep::Real *value
        ) const;

        //! Computes the probability of scattering from 'incoming' direction to
        //! 'outgoing' direction. Both incoming and outgoing directions are
        //! expressed in local space.
        //! Notes: (1) this method must be overridden if the Sample() method is
        //! overridden, (2) this method must return 0.0 if the IsSpecular() method
        //! is defined to return true.
        virtual sheep::Real ComputeScatteringProbability(
            const sheep::Vector3 &incoming,
            const sheep::Vector3 &outgoing
        ) const;

        //! Computes and returns the hemispherical hemispherical reflectance.
        //! Note: this method must be overridden if the IsSpecular() method is defined
        //! to return true.
        virtual sheep::Real ComputeReflectance(const Context &context) const;

        //! Computes and returns the directional hemispherical reflectance. The
        //! incoming direction is expressed in local space.
        //! Note: this method must be overridden if the IsSpecular() method is defined
        //! to return true.
        virtual sheep::Real ComputeReflectance(
            const Context &context,
            const sheep::Vector3 &incoming
        ) const;
    };

    //! Bidirectional Reflectance Distribution Function (BRDF).
    class IBRDF : public IBDF {
    public:
        virtual ~IBRDF() {}
    };

    //! Bidirectional Transmittance Distribution Function (BTDF).
    class IBTDF : public IBDF {
    public:
        virtual ~IBTDF() {}
    };

#include "ibdf.inl"

}

#endif  // !TOXIC_RENDERER_IBDF_H

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