准备一个模糊Shader

将相机视图渲染到texture上

将渲染后的texture赋值给RawImage图片

using UnityEngine;
using UnityEngine.UI;

public class UIBgBlur : MonoBehaviour
{
    // Start is called before the first frame update
    private RawImage blur;
    private Camera uiCamera;
    private Canvas blurCanvas;
    void Start()
    {
        blur = transform.Find("RawImage").GetComponent<RawImage>();
        uiCamera = GameObject.Find("Main Camera").GetComponent<Camera>();
        blurCanvas = GetComponent<Canvas>();
    }

    public void SetSortingOrder(int order)
    {
        blurCanvas.overrideSorting = true;
        blurCanvas.sortingOrder = order;
    }

    public void Show()
    {
        DrawCameraPicture();
    }

    private void DrawCameraPicture()
    {
        // 抓取相机视图转为图片
        RenderTexture targetTexture = new RenderTexture(Screen.width, Screen.height, 24, RenderTextureFormat.ARGB32);
        var texRect = new Rect(0, 0, targetTexture.width, targetTexture.height);
        targetTexture.name = "UIBgBlur_onSceneMemory";
        var tempTexture2D = new Texture2D(targetTexture.width, targetTexture.height, TextureFormat.RGB24, false);
        tempTexture2D.name = "UIBgBlur_onSceneMemory";
        var cameraPrevT = uiCamera.targetTexture;
        uiCamera.targetTexture = targetTexture;    // 设置相机的目标渲染纹理。
        uiCamera.Render();                         // 手动渲染相机
        uiCamera.targetTexture = cameraPrevT;      // 还原相机渲染目标
        RenderTexture.active = targetTexture;      // 设置当前活动的渲染纹理
        tempTexture2D.ReadPixels(texRect, 0, 0);
        tempTexture2D.Apply();
        RenderTexture.active = null;               // 清空
        
        // 赋值给RawImage
        blur.texture = tempTexture2D;
        blur.texture.name = "UIBgBlur_onSceneMemory";
        blur.gameObject.SetActive(true);
    }
}