UE StereoRenderingDevice IStereoRendering

i define a custom stereorendering device , which implemented the interface istereorendering, set the AdjustViewRect, CalculateStereoViewOffset,GetStereoProjectionMatrix etc function ,how can i get the rendering buffer about left and right view?

i can get the gameviewportclient draw function , get total FSceneViewFamily → Rendertarget , but this rendertarget is total scene view , how can i get the seperate view ?