单通道 VR 渲染（通过双宽渲染纹理）。
This is a faster rendering path for VR compared to the StereoRenderingPath.MultiPass.
The speed is achieved by traversing the Scene graph only once while issuing two draw calls for each render node.
主渲染目标必须是一个双宽渲染目标。
场景剔除和阴影贴图渲染在两眼之间处于共享状态。
另请参阅：PlayerSettings.stereoRenderingPath。