rsampler.h

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/*
    This file is part of Mitsuba, a physically based rendering system.

    Copyright (c) 2007-2014 by Wenzel Jakob and others.

    Mitsuba is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License Version 3
    as published by the Free Software Foundation.

    Mitsuba 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 this program. If not, see <http://www.gnu.org/licenses/>.
*/

#pragma once
#if !defined(__MITSUBA_BIDIR_RSAMPLER_H_)
#define __MITSUBA_BIDIR_RSAMPLER_H_

#include <mitsuba/render/sampler.h>

MTS_NAMESPACE_BEGIN

/**
 * \brief Specialized sampler implementation used to seed MLT-style algorithm.
 *
 * Allows to query for the current sample index, which can later be used to rewind
 * back to this state. In the case of MLT, this makes it possible to sample paths
 * approximately proportional to their contribution without actually having
 * to store millions of path. Note that `rewinding' is naive -- it just
 * resets & regenerates the whole random number sequence, which might be slow.
 *
 * \ingroup libbidir
 */
class MTS_EXPORT_BIDIR ReplayableSampler : public Sampler {
public:
        /// Construct a new sampler
        ReplayableSampler();

        /// Unserialize a sampler
        ReplayableSampler(Stream *stream, InstanceManager *manager);

        /**
         * Create a clone of this sampler. The clone is allowed to be different
         * to some extent, e.g. a pseudorandom generator should be based on a
         * different random seed compared to the original. All other parameters,
         * are copied exactly.
         */
        virtual ref<Sampler> clone();

        /* Does nothing in this implementation */
        virtual void advance();
        virtual void generate(const Point2i &pos);

        /// Manually set the current sample index
        virtual void setSampleIndex(size_t sampleIndex);

        /// Retrieve the next component value from the current sample
        virtual Float next1D();

        /// Retrieve the next two component values from the current sample
        virtual Point2 next2D();

        /* Unsupported by this implementation */
        virtual void request2DArray(size_t size);
        virtual void request1DArray(size_t size);

        /// Serialize this sampler to disk
        virtual void serialize(Stream *stream, InstanceManager *manager) const;

        /// Return a string description
        virtual std::string toString() const;

        /// Return the underlying random number generator
        inline Random *getRandom() { return m_random; }

        /**
         * Update the current sample index, but without
         * changing the RNG state. This is useful if the
         * underlying random number generator has been used
         * outside of this class
         */
        inline void updateSampleIndex(size_t index) { m_sampleIndex = index; }

        MTS_DECLARE_CLASS()
protected:
        /// Virtual destructor
        virtual ~ReplayableSampler();
protected:
        ref<Random> m_initial, m_random;
};

MTS_NAMESPACE_END

#endif /* __MITSUBA_BIDIR_RSAMPLER_H_ */