Unity 截图选择框，中间全透明，边缘半透明

效果：点击白色框可拖拽选择区域

 

代码：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;

public class jietu : MonoBehaviour, IDragHandler, IEndDragHandler,IBeginDragHandler
{
    void Start()
    {
        //DrawTriangle(30, 0, 100, 250, 200, 100, mat);//三角形的三个定点坐标
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        dragObj = eventData.rawPointerPress;
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (dragObj!=null)
        {
            dragObj.transform.position = Input.mousePosition;

            leftBottomPos   = leftBottom.transform.position;
            leftTopPos      = leftTop.transform.position;
            rightTopPos     = rightTop.transform.position;
            rightBottomPos = rightBottom.transform.position;

            if (dragObj.Equals(leftBottom))
            {
                leftTopPos.x = dragObj.transform.position.x;
                rightBottomPos.y= dragObj.transform.position.y;
                leftTop.transform.position = leftTopPos;
                rightBottom.transform.position = rightBottomPos;
            }
            else if (dragObj.Equals(leftTop))
            {
                leftBottomPos.x = dragObj.transform.position.x;
                rightTopPos.y = dragObj.transform.position.y;
                leftBottom.transform.position = leftBottomPos;
                rightTop.transform.position = rightTopPos;
            }
            else if (dragObj.Equals(rightTop))
            {
                rightBottomPos.x = dragObj.transform.position.x;
                leftTopPos.y = dragObj.transform.position.y;
                rightBottom.transform.position = rightBottomPos;
                leftTop.transform.position = leftTopPos;
            }
            else if (dragObj.Equals(rightBottom))
            {
                rightTopPos.x = dragObj.transform.position.x;
                leftBottomPos.y = dragObj.transform.position.y;
                rightTop.transform.position = rightTopPos;
                leftBottom.transform.position = leftBottomPos;
            }
        }

    }

    public void OnEndDrag(PointerEventData eventData)
    {
        dragObj = null;
    }

    GameObject dragObj;

    public GameObject leftBottom;
    public GameObject leftTop;
    public GameObject rightTop;
    public GameObject rightBottom;

    Vector2 leftBottomPos   = Vector2.zero;
    Vector2 leftTopPos      = Vector2.zero;
    Vector2 rightTopPos     = Vector2.zero;
    Vector2 rightBottomPos  = Vector2.zero;

    public Material mat;
    void OnRenderObject()
    {
        DrawTriangle();//三角形的三个定点坐标
    }
    void DrawTriangle()
    {
        GL.PushMatrix();
        mat.SetPass(0);
        GL.LoadOrtho();
        GL.Begin(GL.QUADS);//顺时针方向

        //顶部
        GL.Vertex3(leftTop.transform.position.x / Screen.width, leftTop.transform.position.y / Screen.height, 0);
        GL.Vertex3(0, 1, 0);
        GL.Vertex3(1, 1, 0);
        GL.Vertex3(rightTop.transform.position.x / Screen.width, rightTop.transform.position.y / Screen.height, 0);

        //右侧
        GL.Vertex3(rightBottom.transform.position.x / Screen.width, rightBottom.transform.position.y / Screen.height, 0);
        GL.Vertex3(rightTop.transform.position.x / Screen.width, rightTop.transform.position.y / Screen.height, 0);
        GL.Vertex3(1, 1, 0);
        GL.Vertex3(1, 0, 0);

        //底部
        GL.Vertex3(0, 0, 0);//屏幕左下角
        GL.Vertex3(leftBottom.transform.position.x / Screen.width, leftBottom.transform.position.y / Screen.height, 0);//屏幕左上角
        GL.Vertex3(rightBottom.transform.position.x / Screen.width, rightBottom.transform.position.y / Screen.height, 0);//屏幕右上角
        GL.Vertex3(1, 0, 0);//屏幕右下角

        //左侧
        GL.Vertex3(0, 0, 0);
        GL.Vertex3(0, 1, 0);
        GL.Vertex3(leftTop.transform.position.x / Screen.width, leftTop.transform.position.y / Screen.height, 0);
        GL.Vertex3(leftBottom.transform.position.x / Screen.width, leftBottom.transform.position.y / Screen.height, 0);

        GL.End();
        GL.PopMatrix();
    }
}

　　

unity里的设置

改良版：限定剪裁区域的最小范围

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;

public class jietu : MonoBehaviour, IDragHandler, IEndDragHandler, IBeginDragHandler
{
    GameObject dragObj;

    public GameObject leftBottom;
    public GameObject leftTop;
    public GameObject rightTop;
    public GameObject rightBottom;

    Vector2 leftBottomPos;
    Vector2 leftTopPos;
    Vector2 rightTopPos;
    Vector2 rightBottomPos;

    public Material mat;

    public float x_min = 100;
    public float y_min = 100;

    public void OnBeginDrag(PointerEventData eventData)
    {
        dragObj = eventData.rawPointerPress;
        leftBottomPos = leftBottom.transform.position;
        leftTopPos = leftTop.transform.position;
        rightTopPos = rightTop.transform.position;
        rightBottomPos = rightBottom.transform.position;
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (dragObj != null)
        {
            if (dragObj.Equals(leftBottom))
            {
                if ((rightTopPos.x - Input.mousePosition.x) > x_min)
                {
                    leftBottomPos.x = Input.mousePosition.x;
                    leftTopPos.x = Input.mousePosition.x;

                    leftBottom.transform.position = leftBottomPos;
                    leftTop.transform.position = leftTopPos;
                }

                if ((rightTopPos.y - Input.mousePosition.y) > y_min)
                {
                    leftBottomPos.y = Input.mousePosition.y;
                    rightBottomPos.y = Input.mousePosition.y;

                    leftBottom.transform.position = leftBottomPos;
                    rightBottom.transform.position = rightBottomPos;
                }

            }
            else if (dragObj.Equals(leftTop))
            {
                if ((rightBottomPos.x - Input.mousePosition.x) > x_min)
                {
                    leftTopPos.x = Input.mousePosition.x;
                    leftBottomPos.x = Input.mousePosition.x;

                    leftTop.transform.position = leftTopPos;
                    leftBottom.transform.position = leftBottomPos;

                }
                if ((Input.mousePosition.y - rightBottomPos.y) > y_min)
                {
                    leftTopPos.y = Input.mousePosition.y;
                    rightTopPos.y = Input.mousePosition.y;

                    leftTop.transform.position = leftTopPos;
                    rightTop.transform.position = rightTopPos;
                }
            }
            else if (dragObj.Equals(rightTop))
            {
                if ((Input.mousePosition.x - leftBottomPos.x) > x_min)
                {
                    rightTopPos.x = Input.mousePosition.x;
                    rightBottomPos.x = Input.mousePosition.x;

                    rightTop.transform.position = rightTopPos;
                    rightBottom.transform.position = rightBottomPos;
                }
                if ((Input.mousePosition.y - leftBottomPos.y) > y_min)
                {
                    rightTopPos.y = Input.mousePosition.y;
                    leftTopPos.y = Input.mousePosition.y;

                    rightTop.transform.position = rightTopPos;
                    leftTop.transform.position = leftTopPos;
                }
            }
            else if (dragObj.Equals(rightBottom))
            {
                if ((Input.mousePosition.x - leftTopPos.x) > x_min)
                {
                    rightBottomPos.x = Input.mousePosition.x;
                    rightTopPos.x = Input.mousePosition.x;

                    rightBottom.transform.position = rightBottomPos;
                    rightTop.transform.position = rightTopPos;
                }
                if ((leftTopPos.y - Input.mousePosition.y) > y_min)
                {
                    rightBottomPos.y = Input.mousePosition.y;
                    leftBottomPos.y = Input.mousePosition.y;

                    rightBottom.transform.position = rightBottomPos;
                    leftBottom.transform.position = leftBottomPos;
                }
            }
        }
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        dragObj = null;
    }


    void OnRenderObject()
    {
        DrawTriangle();//三角形的三个定点坐标
    }
    void DrawTriangle()
    {
        GL.PushMatrix();
        mat.SetPass(0);
        GL.LoadOrtho();
        GL.Begin(GL.QUADS);//顺时针方向

        //顶部
        GL.Vertex3(leftTop.transform.position.x / Screen.width, leftTop.transform.position.y / Screen.height, 0);
        GL.Vertex3(0, 1, 0);
        GL.Vertex3(1, 1, 0);
        GL.Vertex3(rightTop.transform.position.x / Screen.width, rightTop.transform.position.y / Screen.height, 0);

        //右侧
        GL.Vertex3(rightBottom.transform.position.x / Screen.width, rightBottom.transform.position.y / Screen.height, 0);
        GL.Vertex3(rightTop.transform.position.x / Screen.width, rightTop.transform.position.y / Screen.height, 0);
        GL.Vertex3(1, 1, 0);
        GL.Vertex3(1, 0, 0);

        //底部
        GL.Vertex3(0, 0, 0);//屏幕左下角
        GL.Vertex3(leftBottom.transform.position.x / Screen.width, leftBottom.transform.position.y / Screen.height, 0);//屏幕左上角
        GL.Vertex3(rightBottom.transform.position.x / Screen.width, rightBottom.transform.position.y / Screen.height, 0);//屏幕右上角
        GL.Vertex3(1, 0, 0);//屏幕右下角

        //左侧
        GL.Vertex3(0, 0, 0);
        GL.Vertex3(0, 1, 0);
        GL.Vertex3(leftTop.transform.position.x / Screen.width, leftTop.transform.position.y / Screen.height, 0);
        GL.Vertex3(leftBottom.transform.position.x / Screen.width, leftBottom.transform.position.y / Screen.height, 0);

        GL.End();
        GL.PopMatrix();
    }

}

　　

在实际使用的时候发现用GL画的图像，会导致无法适应UGUI的层级关系，永远位于UI的下层或者上层（取决于Canvas的Render mode），

下面是改良版本，完美适应UI的层级关系

代码如下：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.Serialization;
using UnityEngine.UI;

public class LineChart : MaskableGraphic, IDragHandler, IEndDragHandler, IBeginDragHandler
{


    protected override void OnPopulateMesh(VertexHelper vh)
    {
        vh.Clear();

        UIVertex[] verts0 = new UIVertex[4];

        //顶部
        verts0[0]=SetVertexs(verts0[0], leftTop.transform.localPosition);
        verts0[1]=SetVertexs(verts0[1], screen_leftTopPos);
        verts0[2]=SetVertexs(verts0[2], screen_rightTopPos);
        verts0[3] = SetVertexs(verts0[3], rightTop.transform.localPosition);

        vh.AddUIVertexQuad(verts0);

        UIVertex[] verts1 = new UIVertex[4];
        //右侧
        verts1[0] = SetVertexs(verts1[0], rightBottom.transform.localPosition);
        verts1[1] = SetVertexs(verts1[1], rightTop.transform.localPosition);
        verts1[2] = SetVertexs(verts1[2], screen_rightTopPos);
        verts1[3] = SetVertexs(verts1[3], screen_rightBottomPos);
        vh.AddUIVertexQuad(verts1);

        //底部
        UIVertex[] verts2 = new UIVertex[4];
        verts2[0] = SetVertexs(verts2[0], screen_leftBottomPos);//屏幕左下角
        verts2[1] = SetVertexs(verts2[1], leftBottom.transform.localPosition);//屏幕左上角
        verts2[2] = SetVertexs(verts2[2], rightBottom.transform.localPosition);//屏幕右上角
        verts2[3] = SetVertexs(verts2[3], screen_rightBottomPos);//屏幕右下角
        vh.AddUIVertexQuad(verts2);

        //左侧
        UIVertex[] verts3 = new UIVertex[4];
        verts3[0] = SetVertexs(verts3[0], screen_leftBottomPos);
        verts3[1] = SetVertexs(verts3[1], screen_leftTopPos);
        verts3[2] = SetVertexs(verts3[2], leftTop.transform.localPosition);
        verts3[3] = SetVertexs(verts3[3], leftBottom.transform.localPosition);
        vh.AddUIVertexQuad(verts3);
    }

    GameObject dragObj;

    public GameObject leftBottom;
    public GameObject leftTop;
    public GameObject rightTop;
    public GameObject rightBottom;

    Vector2 leftBottomPos;
    Vector2 leftTopPos;
    Vector2 rightTopPos;
    Vector2 rightBottomPos;

    public float x_min = 100;
    public float y_min = 100;

    readonly Vector2 screen_leftBottomPos= new Vector3(-Screen.width * 0.5f, -Screen.height * 0.5f);
    readonly Vector2 screen_leftTopPos= new Vector3(-Screen.width * 0.5f, Screen.height * 0.5f);
    readonly Vector2 screen_rightTopPos= new Vector3(Screen.width * 0.5f, Screen.height * 0.5f);
    readonly Vector2 screen_rightBottomPos= new Vector3(Screen.width * 0.5f, -Screen.height * 0.5f);

    public void OnBeginDrag(PointerEventData eventData)
    {
        dragObj = eventData.rawPointerPress;
        leftBottomPos = leftBottom.transform.localPosition;
        leftTopPos = leftTop.transform.localPosition;
        rightTopPos = rightTop.transform.localPosition;
        rightBottomPos = rightBottom.transform.localPosition;
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (dragObj != null)
        {
            float x = Input.mousePosition.x - Screen.width * 0.5f;
            float y = Input.mousePosition.y - Screen.height * 0.5f;
            if (dragObj.Equals(leftBottom))
            {
                if ((rightTopPos.x - x) > x_min)
                {
                    leftBottomPos.x = x;
                    leftTopPos.x = x;

                    leftBottom.transform.localPosition = leftBottomPos;
                    leftTop.transform.localPosition = leftTopPos;
                }

                if ((rightTopPos.y - y) > y_min)
                {
                    leftBottomPos.y = y;
                    rightBottomPos.y = y;

                    leftBottom.transform.localPosition = leftBottomPos;
                    rightBottom.transform.localPosition = rightBottomPos;
                }

            }
            else if (dragObj.Equals(leftTop))
            {
                if ((rightBottomPos.x - x) > x_min)
                {
                    leftTopPos.x = x;
                    leftBottomPos.x = x;

                    leftTop.transform.localPosition = leftTopPos;
                    leftBottom.transform.localPosition = leftBottomPos;

                }
                if ((y - rightBottomPos.y) > y_min)
                {
                    leftTopPos.y = y;
                    rightTopPos.y = y;

                    leftTop.transform.localPosition = leftTopPos;
                    rightTop.transform.localPosition = rightTopPos;
                }
            }
            else if (dragObj.Equals(rightTop))
            {
                if ((x - leftBottomPos.x) > x_min)
                {
                    rightTopPos.x = x;
                    rightBottomPos.x = x;

                    rightTop.transform.localPosition = rightTopPos;
                    rightBottom.transform.localPosition = rightBottomPos;
                }
                if ((y - leftBottomPos.y) > y_min)
                {
                    rightTopPos.y = y;
                    leftTopPos.y = y;

                    rightTop.transform.localPosition = rightTopPos;
                    leftTop.transform.localPosition = leftTopPos;
                }
            }
            else if (dragObj.Equals(rightBottom))
            {
                if ((x - leftTopPos.x) > x_min)
                {
                    rightBottomPos.x = x;
                    rightTopPos.x = x;

                    rightBottom.transform.localPosition = rightBottomPos;
                    rightTop.transform.localPosition = rightTopPos;
                }
                if ((leftTopPos.y - y) > y_min)
                {
                    rightBottomPos.y = y;
                    leftBottomPos.y = y;

                    rightBottom.transform.localPosition = rightBottomPos;
                    leftBottom.transform.localPosition = leftBottomPos;
                }
            }
        }

        UpdateGeometry();
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        dragObj = null;
    }


    UIVertex SetVertexs(UIVertex vertex, Vector2 vertexPos)
    {
        vertex.position = vertexPos;
        vertex.color = color;//color是父类中的属性
        vertex.uv0 = Vector2.zero;
        return vertex;
    }

}

　　

 

最终版本：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

public class LineChart : Graphic, IDragHandler, IEndDragHandler, IBeginDragHandler
{
    protected override void OnPopulateMesh(VertexHelper vh)
    {
        vh.Clear();

        //顶部
        verts0[0]=SetVertexs(verts0[0], leftTop.transform.localPosition);
        verts0[1]=SetVertexs(verts0[1], screen_leftTopPos);
        verts0[2]=SetVertexs(verts0[2], screen_rightTopPos);
        verts0[3] = SetVertexs(verts0[3], rightTop.transform.localPosition);
        vh.AddUIVertexQuad(verts0);

        //右侧
        verts1[0] = SetVertexs(verts1[0], rightBottom.transform.localPosition);
        verts1[1] = SetVertexs(verts1[1], rightTop.transform.localPosition);
        verts1[2] = SetVertexs(verts1[2], screen_rightTopPos);
        verts1[3] = SetVertexs(verts1[3], screen_rightBottomPos);
        vh.AddUIVertexQuad(verts1);

        //底部
        verts2[0] = SetVertexs(verts2[0], screen_leftBottomPos);//屏幕左下角
        verts2[1] = SetVertexs(verts2[1], leftBottom.transform.localPosition);//屏幕左上角
        verts2[2] = SetVertexs(verts2[2], rightBottom.transform.localPosition);//屏幕右上角
        verts2[3] = SetVertexs(verts2[3], screen_rightBottomPos);//屏幕右下角
        vh.AddUIVertexQuad(verts2);

        //左侧
        verts3[0] = SetVertexs(verts3[0], screen_leftBottomPos);
        verts3[1] = SetVertexs(verts3[1], screen_leftTopPos);
        verts3[2] = SetVertexs(verts3[2], leftTop.transform.localPosition);
        verts3[3] = SetVertexs(verts3[3], leftBottom.transform.localPosition);
        vh.AddUIVertexQuad(verts3);
    }

    public GameObject leftBottom;
    public GameObject leftTop;
    public GameObject rightTop;
    public GameObject rightBottom;

    public float x_min = 100;
    public float y_min = 100;

    GameObject dragObj;

    Vector2 leftBottomPos;
    Vector2 leftTopPos;
    Vector2 rightTopPos;
    Vector2 rightBottomPos;

    readonly UIVertex[] verts0 = new UIVertex[4];
    readonly UIVertex[] verts1 = new UIVertex[4];
    readonly UIVertex[] verts2 = new UIVertex[4];
    readonly UIVertex[] verts3 = new UIVertex[4];

    readonly Vector2 screen_leftBottomPos= new Vector3(-Screen.width * 0.5f, -Screen.height * 0.5f);
    readonly Vector2 screen_leftTopPos= new Vector3(-Screen.width * 0.5f, Screen.height * 0.5f);
    readonly Vector2 screen_rightTopPos= new Vector3(Screen.width * 0.5f, Screen.height * 0.5f);
    readonly Vector2 screen_rightBottomPos= new Vector3(Screen.width * 0.5f, -Screen.height * 0.5f);

    public void OnBeginDrag(PointerEventData eventData)
    {
        dragObj = eventData.rawPointerPress;
        leftBottomPos   = leftBottom.transform.localPosition;
        leftTopPos      = leftTop.transform.localPosition;
        rightTopPos     = rightTop.transform.localPosition;
        rightBottomPos  = rightBottom.transform.localPosition;
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (dragObj != null)
        {
            float x = Input.mousePosition.x - Screen.width * 0.5f;
            float y = Input.mousePosition.y - Screen.height * 0.5f;
            if (dragObj.Equals(leftBottom))
            {
                if ((rightTopPos.x - x) > x_min)
                {
                    leftBottomPos.x = x;
                    leftTopPos.x = x;

                    leftBottom.transform.localPosition = leftBottomPos;
                    leftTop.transform.localPosition = leftTopPos;
                }
                if ((rightTopPos.y - y) > y_min)
                {
                    leftBottomPos.y = y;
                    rightBottomPos.y = y;

                    leftBottom.transform.localPosition = leftBottomPos;
                    rightBottom.transform.localPosition = rightBottomPos;
                }
            }
            else if (dragObj.Equals(leftTop))
            {
                if ((rightBottomPos.x - x) > x_min)
                {
                    leftTopPos.x = x;
                    leftBottomPos.x = x;

                    leftTop.transform.localPosition = leftTopPos;
                    leftBottom.transform.localPosition = leftBottomPos;

                }
                if ((y - rightBottomPos.y) > y_min)
                {
                    leftTopPos.y = y;
                    rightTopPos.y = y;

                    leftTop.transform.localPosition = leftTopPos;
                    rightTop.transform.localPosition = rightTopPos;
                }
            }
            else if (dragObj.Equals(rightTop))
            {
                if ((x - leftBottomPos.x) > x_min)
                {
                    rightTopPos.x = x;
                    rightBottomPos.x = x;

                    rightTop.transform.localPosition = rightTopPos;
                    rightBottom.transform.localPosition = rightBottomPos;
                }
                if ((y - leftBottomPos.y) > y_min)
                {
                    rightTopPos.y = y;
                    leftTopPos.y = y;

                    rightTop.transform.localPosition = rightTopPos;
                    leftTop.transform.localPosition = leftTopPos;
                }
            }
            else if (dragObj.Equals(rightBottom))
            {
                if ((x - leftTopPos.x) > x_min)
                {
                    rightBottomPos.x = x;
                    rightTopPos.x = x;

                    rightBottom.transform.localPosition = rightBottomPos;
                    rightTop.transform.localPosition = rightTopPos;
                }
                if ((leftTopPos.y - y) > y_min)
                {
                    rightBottomPos.y = y;
                    leftBottomPos.y = y;

                    rightBottom.transform.localPosition = rightBottomPos;
                    leftBottom.transform.localPosition = leftBottomPos;
                }
            }
        }
        UpdateGeometry();
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        dragObj = null;
    }

    UIVertex SetVertexs(UIVertex vertex, Vector2 vertexPos)
    {
        vertex.position = vertexPos;
        vertex.color = color;//color是父类中的属性
        vertex.uv0 = Vector2.zero;
        return vertex;
    }
}