Reprojection

In VR, the image must update for every frame of the display's refresh rate. If a game cannot render a new frame in time, simply repeating the old one would make the world judder as you move your head. Reprojection avoids this by taking the most recent frame and warping it to match your newest head position.

Main kinds

• Rotational reprojection (timewarp) adjusts the last frame for head rotation just before it is shown. Most runtimes use some form of it all the time to cut perceived latency.
• Motion-based reprojection also estimates how objects and the head are moving to synthesize whole in-between frames. Meta calls its versions Asynchronous SpaceWarp (ASW) on PC and Application SpaceWarp (AppSW) on Quest; SteamVR calls its version Motion Smoothing.

When motion-based reprojection is active, the game often runs at half the display rate, such as 45 frames per second on a 90 Hz headset, and the system fills in every other frame.

Side effects

Synthesized frames are guesses, so you may see wobbling or "ghosting" around hands, weapons or fast-moving objects. Reprojection is a safety net, not a replacement for good performance. If you notice these artifacts often on PC, lowering in-game graphics or render resolution usually helps.