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一：实现思路

——UGUI中的OnPopulateMesh函数：

——UGUI提供了ICanvasRaycastFilter接口，实现IsRaycastLocationValid方法，就可以很方便的控制射线是否穿透

二：代码实现

using UnityEngine;using UnityEngine.UI;/// 
/// 镂空遮罩/// 
public class HollowOutMask : Graphic, ICanvasRaycastFilter{    [Header("镂空区域")]    [Space(25)]    public RectTransform inner_trans;    private RectTransform outer_trans;//背景区域    private Vector2 inner_rt;//镂空区域的右上角坐标    private Vector2 inner_lb;//镂空区域的左下角坐标    private Vector2 outer_rt;//背景区域的右上角坐标    private Vector2 outer_lb;//背景区域的左下角坐标    [Header("是否实时刷新")]    [Space(25)]    public bool realtimeRefresh;    protected override void Awake()    {        base.Awake();        outer_trans = GetComponent
   
    ();        //计算边界        CalcBounds();    }    protected override void OnPopulateMesh(VertexHelper vh)    {        if (inner_trans == null)        {            base.OnPopulateMesh(vh);            return;        }        vh.Clear();        UIVertex vertex = UIVertex.simpleVert;        vertex.color = color;        //0 outer左下角        vertex.position = new Vector3(outer_lb.x, outer_lb.y);        vh.AddVert(vertex);        //1 outer左上角        vertex.position = new Vector3(outer_lb.x, outer_rt.y);        vh.AddVert(vertex);        //2 outer右上角        vertex.position = new Vector3(outer_rt.x, outer_rt.y);        vh.AddVert(vertex);        //3 outer右下角        vertex.position = new Vector3(outer_rt.x, outer_lb.y);        vh.AddVert(vertex);        //4 inner左下角        vertex.position = new Vector3(inner_lb.x, inner_lb.y);        vh.AddVert(vertex);        //5 inner左上角        vertex.position = new Vector3(inner_lb.x, inner_rt.y);        vh.AddVert(vertex);        //6 inner右上角        vertex.position = new Vector3(inner_rt.x, inner_rt.y);        vh.AddVert(vertex);        //7 inner右下角        vertex.position = new Vector3(inner_rt.x, inner_lb.y);        vh.AddVert(vertex);        //绘制三角形        vh.AddTriangle(0, 1, 4);        vh.AddTriangle(1, 4, 5);        vh.AddTriangle(1, 5, 2);        vh.AddTriangle(2, 5, 6);        vh.AddTriangle(2, 6, 3);        vh.AddTriangle(6, 3, 7);        vh.AddTriangle(4, 7, 3);        vh.AddTriangle(0, 4, 3);    }    /// 
    
    /// 过滤掉射线检测    /// 
    bool ICanvasRaycastFilter.IsRaycastLocationValid(Vector2 screenPos, Camera eventCamera)    {        if (inner_trans == null)        {            return true;        }        return !RectTransformUtility.RectangleContainsScreenPoint(inner_trans, screenPos, eventCamera);    }    /// 
    
    /// 计算边界    /// 
    private void CalcBounds()    {        if (inner_trans == null)        {            return;        }        Bounds bounds = RectTransformUtility.CalculateRelativeRectTransformBounds(outer_trans, inner_trans);        inner_rt = bounds.max;        inner_lb = bounds.min;        outer_rt = outer_trans.rect.max;        outer_lb = outer_trans.rect.min;    }    private void Update()    {        if (realtimeRefresh == false)        {            return;        }        //计算边界        CalcBounds();        //刷新        SetAllDirty();    }}
   

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