Do I need to use asynchronous reprojection?

With the introduction of asynchronous reprojection back in October 2016, Valve effectively doubled down on their goal to increase the performance of VR games and experiences. This technology builds on what they already had with interleaved reprojection, but many Vive users are still questioning whether or not they want to use it.

Does asynchronous reprojection really make a difference? Should it be used instead of interleaved reprojection or in conjunction with interleaved reprojection? Let's examine exactly what these technologies do and how you can figure out whether or not they're useful to you.

What is asynchronous reprojection?

Enjoying smooth performance

In the beginning, there was interleaved reprojection, Valve's solution for VR games and experiences that don't perform up to snuff. Similar to the Rift's own Asynchronous Spacewarp, this technology fills in frames that can't be rendered in time. Say a game isn't hitting 90FPS; it is forced down to 45FPS and the frame that was previously rendered is injected in place of the frame that would have otherwise been missed.

Asynchronous reprojection is Valve's update to interleaved reprojection. Instead of automatically dropping a VR experience down to 45FPS when it can't hit 90FPS, a frame is intelligently injected when it's clear one will be missed. This effectively removes the judder you sometimes see when interleaved reprojection kicks in and the experience is initially reduced to 45FPS.

Do I need to use asynchronous reprojection?

Valve knows that not everyone can afford a high-end gaming rig, and they also know that not all VR apps are going to perform exceptionally well, even on those high-end rigs. In the patch that brought us asynchronous reprojection, Valve had this to say in the patch notes:

Patch notes from Valve

Whether or not you need to use asynchronous reprojection is quite dependent on your hardware and the experience you're trying to enjoy.

Starting with both reprojection options turned off in SteamVR settings, give the game a try. If you notice that FPS drops are only coming infrequently, you can probably leave interleaved reprojection turned off and only enable asynchronous reprojection. Why? You don't want the game to be dropped down to 45FPS the first time a few frames are dropped when you can let asynchronous reprojection take care of it.

If, however, you disable both reprojections and you experience serious performance issues where the game can't hit 90FPS with any sort of regularity, enabling both reprojection options seems to smooth things right out. In rarer cases, only having interleaved reprojection enabled will be good enough to reach the performance required for a solid VR experience.

How to turn on asynchronous and interleaved reprojection

Enough with all the words; tell me how to enable and disable reprojection!

  1. Launch Steam.
  2. Click the VR button near the top-right corner of the window.

    Launch Steam. Click the VR button.

  3. Click the dropdown button next to SteamVR.
  4. Click Settings.

    Click the dropdown button. Click Settings.

  5. Click Performance.
  6. Click the checkboxes next to the Allow reprojection lines so that a checkmark appears.

    Click Performance. Click the checkboxes.

Monitoring reprojection

SteamVR has a handy tool that lets you monitor your frame timing in a scrolling graph. To see the graph, follow these steps.

  1. Launch Steam.
  2. Click the VR button near the top-right corner of the window.

    Launch Steam. Click the VR button.

  3. Click the dropdown button next to SteamVR.
  4. Click Settings.

    Click the dropdown button. Click Settings.

  5. Click Performance.
  6. Click Display Frame Timing.

    Click Performance. Click Display Frame Timing.

This windows shows you both GPU and CPU performance and will show you when interleaved reprojection kicks in to cap the game at 45FPS.

Frame Timing graph

The red line in the graph shows where interleaved reprojection kicked in when too many frames were being dropped at 90FPS.

For far more information reading the graph and analyzing the data provided by it, check out the Steam Developer Community.

Using Revive

If you are a fan of Revive and use it often to play your Rift games in your Vive, the official word from LibreVR (developers of Revive) is to leave reprojection turned on as some Oculus games rely on it.

Revive answer concerning reprojection

As in any case, if you're seeing poor performance, try playing with either reprojection option turned off to see which combination works best for you and your hardware.

What about AMD?

Radeon RX 480 announcement

Valve's interleaved reprojection was always available for AMD GPU users, but, upon release, asynchronous reprojection was only available for NVIDIA users with driver 372.54 or better.

AMD announced back in February 2017 that they were working on adding asynchronous reprojection support to their GPUs, and the April 2017 ReLive 17.4.1 driver released for Radeon RX 470 and RX 480 cards now delivers this promise, albeit for a limited population.

More information about VR performance

We touched a bit on the technology Oculus employs to boost performance and to also lower minimum specs, but head over to our Timewarp and Spacewarp guide for the full story.

Asynchronous Timewarp, Spacewarp, and why should you care!