void Update () {

        if(Input.GetKeyDown(KeyCode.A))

        {

            StartCoroutine(getScreenTexture());

                           //unity 自带截屏，只能是截全屏

            Application.CaptureScreenshot("shot.png");

        }

    }

    public int capx=;

    public int capy=;

    public int capwidth=;

    public int capheight=;

    IEnumerator getScreenTexture()

    {

        yield return new WaitForEndOfFrame();

        Texture2D t = new Texture2D(capwidth, capheight,TextureFormat.RGB24, true);//需要正确设置好图片保存格式

          t.ReadPixels(new Rect(capx,capy,capwidth,capheight), , , false);//按照设定区域读取像素；注意是以左下角为原点读取

        t.Apply();

        //二进制转换

        byte[] byt = t.EncodeToPNG();

        File.WriteAllBytes(Application.dataPath  + Time.time + ".png", byt);

    }