quicktex/src/interpolator.h

/*  Python-rgbcx Texture Compression Library
    Copyright (C) 2021 Andrew Cassidy <drewcassidy@me.com>
    Partially derived from rgbcx.h written by Richard Geldreich <richgel99@gmail.com>
    and licenced under the public domain

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program 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 Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#pragma once
#include <array>
#include <cassert>
#include <cstdint>
#include <memory>

#include "Color.h"
#include "ndebug.h"
#include "util.h"

namespace rgbcx {

class Interpolator {
   public:
    enum class Type { Ideal, IdealRound, Nvidia, AMD };

    static std::unique_ptr<Interpolator> MakeInterpolator(Type type = Type::Ideal);

    virtual ~Interpolator() noexcept = default;

    /**
     * Performs a 2/3 interpolation of a pair of 5-bit values to produce an 8-bit value
     * Output is approximately (2v0 + v1)/3, with v0 and v1 first extended to 8 bits.
     * @param v0 The first 5-bit value
     * @param v1 The second 5-bit value
     * @return The interpolated value
     */
    virtual uint8_t Interpolate5(uint8_t v0, uint8_t v1) const;

    /**
     * Performs a 2/3 interpolation of a pair of 5-bit values to produce an 8-bit value
     * Output is approximately (2v0 + v1)/3, with v0 and v1 first extended to 8 bits.
     * @param v0 The first 5-bit value
     * @param v1 The second 5-bit value
     * @return The interpolated value
     */
    virtual uint8_t Interpolate6(uint8_t v0, uint8_t v1) const;

    /**
     * Performs a 1/2 interpolation of a pair of 5-bit values to produce an 8-bit value
     * Output is approximately (v0 + v1)/2, with v0 and v1 first extended to 8 bits.
     * @param v0 The first 5-bit value
     * @param v1 The second 5-bit value
     * @return The interpolated value
     */
    virtual uint8_t InterpolateHalf5(uint8_t v0, uint8_t v1) const;

    /**
     * Performs a 1/2 interpolation of a pair of 6-bit values to produce an 8-bit value
     * Output is approximately (v0 + v1)/2, with v0 and v1 first extended to 8 bits.
     * @param v0 The first 6-bit value
     * @param v1 The second 6-bit value
     * @return The interpolated value
     */
    virtual uint8_t InterpolateHalf6(uint8_t v0, uint8_t v1) const;

    /**
     * Generates the 4 colors for a BC1 block from the given 5:6:5-packed colors
     * @param low first 5:6:5 color for the block
     * @param high second 5:6:5 color for the block
     * @return and array of 4 Color values, with indices matching BC1 selectors
     */
    virtual std::array<Color, 4> InterpolateBC1(uint16_t low, uint16_t high) const;

    /**
     * Gets the type of an interpolator
     * @return The interpolator type
     */
    virtual Type GetType() const noexcept { return Type::Ideal; }

    /**
     * Checks if the interpolator uses an ideal algorithm
     * @return true if the interpolator is ideal, false otherwise.
     */
    virtual bool IsIdeal() const noexcept {
        auto type = GetType();
        return (type == Type::Ideal || type == Type::IdealRound);
    }

   private:
    virtual uint8_t Interpolate8(uint8_t v0, uint8_t v1) const;
    virtual uint8_t InterpolateHalf8(uint8_t v0, uint8_t v1) const;

    //    constexpr static auto Expand5 = ExpandArray<Size5, scale5To8>();
    //    constexpr static auto Expand6 = ExpandArray<size6, scale6To8>();
    //
    //    // match tables used for single-color blocks
    //    using MatchList = std::array<MatchEntry, match_count>;
    //    using MatchListPtr = std::shared_ptr<MatchList>;
    //
    //    const MatchListPtr _single_match5 = {std::make_shared<MatchList>()};
    //    const MatchListPtr _single_match6 = {std::make_shared<MatchList>()};
    //    const MatchListPtr _single_match5_half = {std::make_shared<MatchList>()};
    //    const MatchListPtr _single_match6_half = {std::make_shared<MatchList>()};

    Color InterpolateColor24(const Color &c0, const Color &c1) const {
        return Color(Interpolate8(c0.r, c1.r), Interpolate8(c0.g, c1.g), Interpolate8(c0.b, c1.b));
    }

    Color InterpolateHalfColor24(const Color &c0, const Color &c1) const {
        return Color(InterpolateHalf8(c0.r, c1.r), InterpolateHalf8(c0.g, c1.g), InterpolateHalf8(c0.b, c1.b));
    }

    //    virtual constexpr bool useExpandedInMatch() noexcept { return true; }
    //
    //    void PrepSingleColorTables(const MatchListPtr &matchTable, const MatchListPtr &matchTableHalf, int len);
    //
    //    int PrepSingleColorTableEntry(const MatchListPtr &matchTable, int v, int i, int low, int high, int low_e, int high_e, int lowest_error, bool half,
    //                                  bool ideal);
};

class InterpolatorRound : public Interpolator {
   public:
    uint8_t Interpolate5(uint8_t v0, uint8_t v1) const override;
    uint8_t Interpolate6(uint8_t v0, uint8_t v1) const override;
    Type GetType() const noexcept override { return Type::IdealRound; }

   private:
    uint8_t Interpolate8(uint8_t v0, uint8_t v1) const override;
};

class InterpolatorNvidia : public Interpolator {
   public:
    uint8_t Interpolate5(uint8_t v0, uint8_t v1) const override;
    uint8_t Interpolate6(uint8_t v0, uint8_t v1) const override;
    uint8_t InterpolateHalf5(uint8_t v0, uint8_t v1) const override;
    uint8_t InterpolateHalf6(uint8_t v0, uint8_t v1) const override;
    std::array<Color, 4> InterpolateBC1(uint16_t low, uint16_t high) const override;
    Type GetType() const noexcept override { return Type::Nvidia; }

   private:
    Color InterpolateColor565(const Color &c0, const Color &c1) const {
        return Color(Interpolate5(c0.r, c1.r), Interpolate6(c0.g, c1.g), Interpolate5(c0.b, c1.b));
    }

    Color InterpolateHalfColor565(const Color &c0, const Color &c1) const {
        return Color(InterpolateHalf5(c0.r, c1.r), InterpolateHalf6(c0.g, c1.g), InterpolateHalf5(c0.b, c1.b));
    }
};

class InterpolatorAMD : public Interpolator {
   public:
    uint8_t Interpolate5(uint8_t v0, uint8_t v1) const override;
    uint8_t Interpolate6(uint8_t v0, uint8_t v1) const override;
    uint8_t InterpolateHalf5(uint8_t v0, uint8_t v1) const override;
    uint8_t InterpolateHalf6(uint8_t v0, uint8_t v1) const override;
    Type GetType() const noexcept override { return Type::AMD; }

   private:
    uint8_t Interpolate8(uint8_t v0, uint8_t v1) const override;
    uint8_t InterpolateHalf8(uint8_t v0, uint8_t v1) const override;
};
}  // namespace rgbcx