code: private void captureEye(GVRScreenshotCallback callback, GVRRenderTarget renderTarget, GVRViewManager.EYE eye, boolean useMultiview) {
          if (null == callback) {
              return;
          }
          readRenderResult(renderTarget,eye,useMultiview);
          returnScreenshotToCaller(callback, mReadbackBufferWidth, mReadbackBufferHeight);
      }
docs: capture screenshot of an eye