截屏，截图

1......使用Application 提供的api

   Application.CaptureScreenshot(Application.dataPath + "/11.png");

2.....利用Texture2D提供的函数 ReadPixels，注意要在每帧渲染完成后才能使用，

否则会抛出异常： ReadPixels was called to read pixels from system frame buffer, while not inside drawing frame.，该函数是从 读取的  RenderTexture. active。下面是文档说明

This will copy a rectangular pixel area from the currently active RenderTexture or the view (specified by the source parameter) into the position defined by destX anddestY. Both coordinates use pixel space - (0,0) is lower left.

   IEnumerator Cap()
    {
        yield return new WaitForEndOfFrame();

        Texture2D tex = new Texture2D(Screen.width, Screen.height);

        tex.ReadPixels(new Rect(Vector2.zero, new Vector2(Screen.width, Screen.height)), 0, 0);
        var raw = tex.EncodeToPNG();
        string filename = Application.dataPath + "/111.png";

        System.IO.File.WriteAllBytes( filename, raw);
    }

3.......摄像机可以Render到RenderTexture 然后执行保存相关操作