ATouchScroller.h

/*
 * AUI Framework - Declarative UI toolkit for modern C++20
 * Copyright (C) 2020-2024 Alex2772 and Contributors
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
#pragma once
 
 
#include "AUI/Common/AObject.h"
#include "AUI/Event/APointerPressedEvent.h"
#include "AUI/Event/APointerReleasedEvent.h"
#include "AMetric.h"
#include "AUI/Event/AScrollEvent.h"
#include "AUI/Animator/Curves/bezier.h"
 
class API_AUI_VIEWS ATouchScroller {
public:
    /*
     * @brief Deceleration for kinetic scroll
     * @note Multiply by dpi ratio for proper work of kinetic scroll on all devices
     */
    static constexpr float BASE_DECELERATION = 1600.f;
 
    static constexpr float INITIAL_ACCELERATION_COEFFICIENT = 60.f;
 
    static float deceleration();
 
    static constexpr AMetric THRESHOLD = 8_dp;
 
    ATouchScroller() = default;
 
    void handlePointerPressed(const APointerPressedEvent& e);
 
    void handlePointerReleased(const APointerReleasedEvent& e);
 
    glm::ivec2 handlePointerMove(glm::vec2 pos);
 
    [[nodiscard]]
    glm::ivec2 origin() const noexcept;
 
    [[nodiscard]]
    AOptional<glm::ivec2> gatherKineticScrollValue();
 
private:
    struct WaitingForThresholdState {
        APointerIndex pointer;
        glm::vec2 origin;
    };
    struct ScrollingState {
        APointerIndex pointer;
        glm::vec2 origin;
        glm::vec2 previousPosition = {0.f, 0.f}; // to calculate velocity
        glm::vec2 currentVelocity = {0.f, 0.f};
        glm::vec2 prevVelocity = {0.f, 0.f};
        glm::vec2 prevPrevVelocity = {0.f, 0.f};
        std::chrono::microseconds timeBetweenFrames;
        AOptional<std::chrono::high_resolution_clock::time_point> lastFrameTime;
    };
 
    struct KineticScrollingState {
        APointerIndex pointer;
        glm::vec2 origin;
        float velocity;
        float averageTimeDelta;
        glm::vec2 direction;
 
        std::chrono::high_resolution_clock::time_point lastFrameTime = std::chrono::high_resolution_clock::now();
    };
 
    std::variant<std::nullopt_t, WaitingForThresholdState, ScrollingState, KineticScrollingState> mState = std::nullopt;
};