Crafter.Graphics/interfaces/Crafter.Graphics-Animation.cppm

/*
Crafter®.Graphics
Copyright (C) 2025 Catcrafts®
Catcrafts.net

This library 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 3.0 of the License, or (at your option) any later version.

This library 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 library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
*/

export module Crafter.Graphics:Animation;
import std;

namespace Crafter {
    template <typename T>
    constexpr T Lerp(T a, T b, double elapsed) {
        return a + static_cast<T>(elapsed * (b - a));
    }

    // Template specialization for std::string
    template <>
    std::string Lerp<std::string>(std::string a, std::string b, double elapsed) {
        // Clamp elapsed to [0, 1]
        if (elapsed < 0.0) elapsed = 0.0;
        if (elapsed > 1.0) elapsed = 1.0;

        // Number of characters from b to reveal
        std::size_t len = static_cast<std::size_t>(std::floor(b.size() * elapsed));

        return a + b.substr(0, len);
    }

    template <typename Tuple, std::size_t... Is>
    constexpr auto LerpTupleImpl(const Tuple& a, const Tuple& b, double elapsed, std::index_sequence<Is...>) {
        return std::make_tuple(Lerp(std::get<Is>(a), std::get<Is>(b), elapsed)...);
    }

    template <typename Tuple>
    constexpr auto LerpTuple(const Tuple& a, const Tuple& b, double elapsed) {
        return LerpTupleImpl(a, b, elapsed, std::make_index_sequence<std::tuple_size_v<Tuple>>{});
    }

    export template <typename T>
    struct Keyframe{
        std::chrono::duration<double> duration;
        T values;
    };

    export template <typename T>
    struct Animation {
        std::vector<Keyframe<T>> keyframes;
        std::uint_fast32_t currentFrame;
        std::chrono::time_point<std::chrono::high_resolution_clock> startedAt;
        Animation(std::vector<Keyframe<T>>&& keyframes) : keyframes(std::move(keyframes)) {}
        void Start(std::chrono::time_point<std::chrono::high_resolution_clock> time) {
            currentFrame = 0;
            startedAt = time;
        }
        T Play(std::chrono::time_point<std::chrono::high_resolution_clock> time) {
            std::chrono::duration<double> elapsed = time - startedAt;  // elapsed time since animation started
            std::chrono::duration<double> accumulated(0);

            for (std::uint_fast32_t i = currentFrame; i < keyframes.size() - 1; ++i) {
                accumulated += keyframes[i+1].duration;
                if (elapsed < accumulated) {
                    std::chrono::duration<double> frameStartTime = accumulated - keyframes[i+1].duration;
                    auto t = (elapsed - frameStartTime) / keyframes[i+1].duration.count();

                    currentFrame = i;
                    return LerpTuple(
                        keyframes[i].values,
                        keyframes[i + 1].values,
                        t.count()
                    );
                }
            }

            // If we get here, we're past the last keyframe
            currentFrame = keyframes.size() - 1;
            return keyframes.back().values;
        }
    };
}