To be fully immersed into an interactive VR Environment, more and more power is required to GPU and CPU as the HMD (Head Mounted Display) devices increase their specifications.
At Oculus for the Rift PC runtime platform have been implemented two key solutions that managing the image frame rate literally upgrade the GPU and CPU, in way to perform High Quality VR on low performing hardware as well.
The first one has been Asynchronous Timewarp (ATW) on Windows.
ATW, on a general-purpose multitasking OS like Windows, can manage background applications that can affect the VR performances. ATW, released on March 2016, is able to decouple timewarp from the rendering loop in way to run independently and asynchronously GP an CPU workload and background apps. Relying on CPU and GPU pre-emption, ATW picks up the latest available application frame and timewarp it before each display scanout at 90Hz.
The next step has been few months later on November 2016 the release of Asynchronous Spacewarp (ASW) a frame-rate smoothing technique that almost halves the CPU/GPU time required to produce nearly the same output from the same content. Like Asynchronous Timewarp (ATW), ASW is automatic and enabled without any additional effort from developers.
That said, Oculus has announced that ASW has been brought to the stage 2.0 activating to support headset performance in a full 6DOF space, accounting for depth and rotation. ASW 2.0 combines ASW with an existing experimental technology, Positional Timewarp (PTW) to take the Oculus PC runtime prediction accuracy to the next level and further boost app performance and frame rate.
Benefits of ASW 2.0
- Improving performance with severe frame rate drop: ASW 1.0 impact peaks at half the native frame rate of a headset (e.g. 45hz for Oculus Rift). However, in some instances, if an app drops below half frame rate, ASW can’t perform acceptably. Even at reduced frame rate, ASW 2.0 can maintain an acceptable view in VR, as PTW’s depth-based reprojection works more accurately for lower frame rates than ASW 1.0 extrapolation.
- Lowering 6DOF headset tracking latency:Previously, the Oculus PC runtime would only correct for 3DOF headset rotation to decrease tracking latency. With ASW 2.0 and PTW, even if ASW doesn’t need to activate, PTW will continue to provide low-latency 6DOF HMD tracking—regardless of the VR app’s frame rate.
- Reprojecting repeating patterns and visually similar content:What happens when you have a zebra standing behind a white picket fence? While that exact scenario may be rare, checkerboard and lined patterns are extremely common in VR and present challenges for ASW 1.0—particularly when they’re layered. With ASW 2.0, we can use depth data to separate the objects before extrapolating, which lets us solve reprojection errors. See the following clip for a visual demonstration of how this works in ASW 1.0 vs. 2.0.
ASW 2.0 in Action
ASW 2.0 asks developers to expose depth information. With the Rift system interface Dash, the Oculus PC runtime already uses PTW to smooth performance, blending the Dash interface over an app’s depth-composition layers.
As such, most Rift apps on the Oculus Store built on Unreal Engine 4 and Unity already provide the depth information required to make ASW 2.0 work. As more apps provide this information, ASW 2.0 support will become increasingly ubiquitous.
For applications that don’t provide the necessary depth data, the Oculus PC runtime will revert to ASW 1.0.