ATouchScroller.h

/*
 * AUI Framework - Declarative UI toolkit for modern C++20
 * Copyright (C) 2020-2025 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;
};

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