@supersid333 i think this image portrays it fairly well basically the viewport moves around at your refresh rate, and game renders are positioned at the center of your view in space every frame, and stick there in space when you look around
the result is an incredibly smooth experience even at low fps, allows VR to work at all with low performance and how motion sick prone humans are
at crazy low framerates and high movement speeds you can get black borders in your view as shown in the image, but that can managed by rendering at a higher fov than the viewport