lanczos_filter.h

// Description: Lanczos_Filter class
// Detail: Lanczos reconstruction filter
// Documentation: filters.txt

#ifndef PASTELGFX_LANCZOS_FILTER_H
#define PASTELGFX_LANCZOS_FILTER_H

#include "pastel/gfx/filter.h"

#include "pastel/sys/math/sinc.h"

#include <cmath>

namespace Pastel
{

    //! Lanczos reconstruction filter.
    /*!
   This filter is interpolatory. It is given by
   f(x) = sinc(|x|) * sinc(|x| / radius), |x| < radius
                                       0, otherwise
   */
    class Lanczos_Filter
        : public Filter
    {
    public:
        // Using default copy constructor.
        // Using default assignment.

        explicit Lanczos_Filter(real radius = 2)
        : Filter(radius, "lanczos")
        , invRadius_(inverse(radius))
        {
        }

        virtual ~Lanczos_Filter()
        {
        }

        virtual real evaluateInRange(real x) const
        {
            return sinc<real>(x) * sinc<real>(x * invRadius_);
        }

    private:
        Lanczos_Filter(const Lanczos_Filter& that) = delete;
        Lanczos_Filter& operator=(const Lanczos_Filter& that) = delete;

        virtual void onSetRadius()
        {
            invRadius_ = inverse(radius());
        }

        real invRadius_;
    };

    using LanczosFilterPtr = std::shared_ptr<Lanczos_Filter>;
    using ConstLanczosFilterPtr = std::shared_ptr<const Lanczos_Filter>;

    inline LanczosFilterPtr lanczosFilter(real radius = 2)
    {
        return std::make_shared<Lanczos_Filter>(radius);
    }

}

#endif