unity拖拽图片放大，缩小

### 如何在 Unity 中实现图片的拖拽、放大和缩小功能

#### 创建 UI Image 组件并设置交互属性
为了使 `Image` 可以被拖动，在 Canvas 下创建一个 `Image` 并为其添加必要的组件。确保该图像具有合适的锚点配置以便于操作。

#### 添加事件监听器处理触摸输入
对于触控设备或鼠标输入的支持，需编写 C# 脚本来捕捉用户的点击动作以及移动手势：

using UnityEngine;
using UnityEngine.EventSystems;

public class DragZoomPan : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    private Vector3 startPosition; // 记录起始位置
    private bool isDragging = false; // 标记是否正在拖拽
    
    public void OnBeginDrag(PointerEventData eventData)
    {
        if (eventData.button != PointerEventData.InputButton.Left) return;
        
        startPosition = transform.position;
        isDragging = true;
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (!isDragging || eventData.button != PointerEventData.InputButton.Left) return;
        
        float deltaX = eventData.delta.x * Time.deltaTime * 10f;
        float deltaY = eventData.delta.y * Time.deltaTime * 10f;
        
        transform.Translate(new Vector3(deltaX, deltaY, 0));
    }
    
    public void OnEndDrag(PointerEventData eventData)
    {
        isDragging = false;
    }
}

此部分实现了基本的拖拽逻辑[^2]。

#### 实现缩放功能
要支持双指捏合来调整大小，则需要额外检测多点触碰情况，并据此改变目标物体的比例尺：

private Camera mainCamera;
private Transform targetTransform;
private float startDistanceBetweenFingers;
private float scaleFactor = 0.5f;

void Start()
{
    mainCamera = Camera.main;
}

// Update is called once per frame
void Update()
{
    HandlePinchToZoom();
}

void HandlePinchToZoom()
{
    if (Input.touchCount == 2)
    {
        Touch touchZero = Input.GetTouch(0);
        Touch touchOne = Input.GetTouch(1);

        Vector2 touchZeroPrevPos = touchZero.position - touchZero.deltaPosition;
        Vector2 touchOnePrevPos = touchOne.position - touchOne.deltaPosition;

        float prevMagnitude = (touchZeroPrevPos - touchOnePrevPos).magnitude;
        float currentMagnitude = (touchZero.position - touchOne.position).magnitude;

        float difference = currentMagnitude - prevMagnitude;

        if (difference > 0 && !float.IsInfinity(difference))
            ScaleObject(true); // 放大
        else if (difference < 0 && !float.IsInfinity(difference))
            ScaleObject(false); // 缩小
        
        startDistanceBetweenFingers = Mathf.Abs(currentMagnitude);
    }   
}

void ScaleObject(bool increaseScale)
{
    Vector3 scaleChangeAmount = new Vector3(scaleFactor, scaleFactor, 0);
    if(increaseScale){
        targetTransform.localScale += scaleChangeAmount;
    }else{
        targetTransform.localScale -= scaleChangeAmount;
    }
}

上述代码片段展示了如何响应两个手指之间的距离变化来进行相应的缩放操作[^1].