public Camera cam;

    void Start()

    {

        StartCoroutine(CaptureAlphaCamera(cam,new Rect(0,0,1920,1080)));

    }

    #region 截取透明图

    /// <summary>

    /// 3.对相机截图。

    /// </summary>

    IEnumerator CaptureAlphaCamera(Camera camera,Rect rect) {

        yield return new WaitForEndOfFrame();

        // 创建一个RenderTexture对象

        RenderTexture rt = new RenderTexture((int)Screen.width,(int)Screen.height,0);

        // 临时设置相关相机的targetTexture为rt, 并手动渲染相关相机

        camera.targetTexture = rt;

        camera.Render();

        RenderTexture.active = rt;

        Texture2D screenShot = new Texture2D((int)rect.width,(int)rect.height,TextureFormat.ARGB32,false);

        screenShot.ReadPixels(rect,0,0);

        screenShot.Apply();

        // 重置相关参数，以使用camera继续在屏幕上显示

        camera.targetTexture = null;

        RenderTexture.active = null; // JC: added to avoid errors

        GameObject.Destroy(rt);

        // 最后将这些纹理数据，成一个png图片文件

        byte[] bytes = screenShot.EncodeToPNG();

        string filename = Application.dataPath + "/Screenshot.png";

        System.IO.File.WriteAllBytes(filename,bytes);

        Debug.Log(string.Format("截屏了一张照片: {0}",filename));

        //及时垃圾清理

        System.GC.Collect();

        //return screenShot;

    }