{"category": "Unity Engine/Runtime/Input", "keywords": "Unity, Runtime, Input, UI, Touch, Mouse, Drag, Zoom"} Detects touch screen or mouse input in the specified UI area.

GraphicInput.cs

using System;
using UnityEngine;
using UnityEngine.Assertions;
using UnityEngine.EventSystems;
using UnityEngine.UI;
using UInput = UnityEngine.Input;

public interface IGraphicInputProvider
{
    public Vector2 Drag { get; }
    public float Zoom { get; }

    void SetEnable(bool enable);
}

[DefaultExecutionOrder(-99)]
[DisallowMultipleComponent]
[RequireComponent(typeof(Graphic))] // Used to detects input area, works with IPointerXXXHandler
public class GraphicInput : MonoBehaviour, IGraphicInputProvider,
    IPointerDownHandler, IPointerUpHandler, IPointerEnterHandler, IPointerExitHandler
{
    #region IGraphicInputProvider

    public Vector2 Drag { get; private set; }
    public float Zoom { get; private set; }


    public void SetEnable(bool enable)
    {
        this.enabled = enable;
    }

    #endregion


    #region Unity消息

    private void OnEnable()
    {
        _touchSupported = UInput.touchSupported;
    }

    private void OnDisable()
    {
        _touchInputMode = TouchInputMode.None;
        _captureMouseZoom = false;
        _captureMouseDrag = false;
        Drag = default;
        Zoom = default;
    }

    private void Update()
    {
        if (DetectTouchInputMode())
        {
            UpdateTouchInput();
        }
        else
        {
            UpdateMouseInput();
        }
    }

    #endregion


    #region IPointerXXXHandler

    void IPointerEnterHandler.OnPointerEnter(PointerEventData eventData)
    {
        _captureMouseZoom = true;
    }

    void IPointerExitHandler.OnPointerExit(PointerEventData eventData)
    {
        _captureMouseZoom = false;
    }

    void IPointerDownHandler.OnPointerDown(PointerEventData eventData)
    {
        _touchCount++;
        _captureMouseDrag = true;
        _lastMousePosition = eventData.position;
    }

    void IPointerUpHandler.OnPointerUp(PointerEventData eventData)
    {
        _touchCount--;
        _captureMouseDrag = false;

        Assert.IsTrue(_touchCount >= 0);
    }

    #endregion


    #region Touch Input

    private bool _touchSupported;
    private int _touchCount;
    private TouchInputMode _touchInputMode = TouchInputMode.None;
    private Vector2 _lastPointer0Position;
    private float _lastTwoPointersDistance;


    private bool DetectTouchInputMode()
    {
        if (!_touchSupported)
        {
            return _touchInputMode != TouchInputMode.None;
        }

        TouchInputMode newTouchInputMode;
        if (_touchCount == 0)
        {
            newTouchInputMode = TouchInputMode.None;
        }
        else
        {
            // The update timing of Input.touchCount and OnPointerDown is inconsistent,
            // do not use the cached _touchCount here.
            // https://forum.unity.com/threads/the-update-timing-of-input-touchcount-is-later-than-ipointeruphandler-onpointerup.1601727/
            switch (UInput.touchCount)
            {
                case 0:
                    newTouchInputMode = TouchInputMode.None;
                    break;
                case 1:
                    newTouchInputMode = TouchInputMode.Drag;
                    break;
                default:
                    newTouchInputMode = TouchInputMode.Zoom;
                    break;
            }
        }

        if (newTouchInputMode == _touchInputMode)
        {
            return _touchInputMode != TouchInputMode.None;
        }

        switch (newTouchInputMode)
        {
            case TouchInputMode.None:
                ExitTouchInput();
                break;
            case TouchInputMode.Drag:
                EnterTouchDragMode(UInput.mousePosition);
                break;
            case TouchInputMode.Zoom:
                EnterTouchZoomMode();
                break;
            default:
                throw new ArgumentOutOfRangeException();
        }

        return _touchInputMode != TouchInputMode.None;
    }

    private void ExitTouchInput()
    {
        Assert.IsTrue(UInput.touchCount == 0);

        _touchInputMode = TouchInputMode.None;
        Zoom = default;
        Drag = default;
    }

    private void EnterTouchDragMode(Vector2 pointer0Position)
    {
        Assert.IsTrue(UInput.touchCount == 1);

        _touchInputMode = TouchInputMode.Drag;
        _lastPointer0Position = pointer0Position;
        Drag = default;
        Zoom = default;
    }

    private void EnterTouchZoomMode()
    {
        Assert.IsTrue(UInput.touchCount > 1);

        _touchInputMode = TouchInputMode.Zoom;
        Vector2 pointer0Pos = UInput.GetTouch(0).position;
        Vector2 pointer1Pos = UInput.GetTouch(1).position;
        _lastTwoPointersDistance = Vector2.Distance(pointer0Pos, pointer1Pos);
        Drag = default;
        Zoom = default;
    }

    private void UpdateTouchInput()
    {
        switch (_touchInputMode)
        {
            case TouchInputMode.None:
                Zoom = default;
                Drag = default;
                break;

            case TouchInputMode.Drag:
            {
                Vector2 pointer0Pos = UInput.GetTouch(0).position;
                Drag = pointer0Pos - _lastPointer0Position;
                _lastPointer0Position = pointer0Pos;
                break;
            }

            case TouchInputMode.Zoom:
            {
                Vector2 pointer0Pos = UInput.GetTouch(0).position;
                Vector2 pointer1Pos = UInput.GetTouch(1).position;
                float twoPointersDist = Vector2.Distance(pointer0Pos, pointer1Pos);
                float distanceDelta = twoPointersDist - _lastTwoPointersDistance;
                _lastTwoPointersDistance = twoPointersDist;
                Zoom = distanceDelta;
                break;
            }

            default:
                throw new ArgumentOutOfRangeException();
        }
    }


    private enum TouchInputMode
    {
        None,
        Drag,
        Zoom,
    }

    #endregion


    #region Mouse Input

    private bool _captureMouseDrag;
    private bool _captureMouseZoom;
    private Vector2 _lastMousePosition;


    private void UpdateMouseInput()
    {
        if (_captureMouseDrag)
        {
            // In the Editor, if the mouse clicks outside the Game window and then returns to the Game window
            // to get Mouse X, Y, the values obtained will be very large, causing the viewport to jump
            // float h = Input.GetAxis("Mouse X");
            // float v = Input.GetAxis("Mouse Y");
            // Drag = new Vector2(h, v);

            Vector2 mousePosition = UInput.mousePosition;
            Drag = mousePosition - _lastMousePosition;
            _lastMousePosition = mousePosition;
        }
        else
        {
            Drag = default;
        }

        if (_captureMouseZoom)
        {
            Zoom = UInput.GetAxis("Mouse ScrollWheel");
        }
        else
        {
            Zoom = default;
        }
    }

    #endregion
}