Horizon OS: Physics, Resource Management & Performance Framework

[Note: Hyphens (-) are used in place of underscores (_) in technical terms to ensure forum system compatibility]

Executive Summary

High-complexity applications and games on standalone Meta Quest headsets often suffer from recurring processing bottlenecks in physics and graphics calculations. This is caused by strict adherence to high screen refresh rates (90Hz / 120Hz) and high per-eye display resolutions, lacking sufficient flexibility to adapt resource consumption dynamically to interactive moments.

This proposal introduces a software architecture vision via Horizon OS and the Meta XR SDK to mitigate these bottlenecks and maximize the computational capacity of the CPU, GPU, and RAM through dynamic control layers and standardized performance profiles that balance visual realism with competitive responsiveness.

HARDWARE CONSTRAINTS AND THERMAL CEILING

- Thermal Management and Conduction: Thermal conductivity limits of the PC-ABS casing require maintaining heat dissipation within a safe operating range without relying on aggressive overclocking.

- TDP Limit: Operating within the operational thermal envelope of standalone headsets (5.0 to 10.0+ Watts) requires meticulous management of CPU and GPU cycles.

- Engineering Approach: Complete focus on software architecture optimization, minimizing memory bandwidth consumption, and improving frame scheduling at the Compositor and SDK levels in tight integration with game engines.

PROCESSING AND GRAPHICS OPTIMIZATIONS VIA HORIZON OS AND META XR SDK

A. Latency Management and Stable Scheduling for AppSW

- Independent Prediction Algorithm: Developing a predictive algorithm at the Compositor level that reads frame timing budget pressure indicators and issues early signals to the game engine to flexibly reduce graphical details before actual frame drops occur.

- Dual Processing Mechanism and Refresh Rates: Upon activating Application SpaceWarp via the XR-FB-space-warp extension, adopt the most stable standard in the ecosystem, such as lowering scene processing rate to 45 FPS with synthetic frame generation to match 90Hz, or 60 FPS doubled to 120Hz depending on the game budget, with pre-initialization of motion vector buffers and depth memory to prevent transient memory bottlenecks and frame pacing jitter.

- Timing Budget and Responsiveness: Granting the application the real-frame processing timing budget, while the Compositor allocates a short, targeted maximum time window to compute and generate the synthetic frame and assemble it prior to the V-Sync signal.

- Input Processing and Hand Controllers: Leveraging head-tracking prediction technologies, enhance and adapt predictive algorithms for hand controller pose prediction to prevent any perceived hand response latency during reduced actual rendering rates.

B. Spatial Physics LOD API

Providing helper software tools within the Meta XR SDK for direct integration with game engines like Unity, Unreal, and Godot to elevate physics performance while stabilizing fixed-timestep simulation, including hardware fallback mechanisms:

- Interactive Zone for Nearby and Interacting Bodies: Processing physics at full resolution and calculating all collisions and interactive effects to ensure sensory response within a unified global fixed timestep.

- Background Zone for Distant and Non-Interactive Bodies: Decoupling background objects from the core physics loop by reducing the simulation sub-stepping and tick rate, relying on visual interpolation to ensure smooth motion continuity. This is integrated with a position blending mechanism with momentum conservation algorithms at the boundaries of returning to the interactive zone to prevent force explosion or sharp snaps.

C. Direct Rendering and GMEM Memory Optimization

Enhancing integration between the Vulkan interface in Horizon OS supporting the VK-KHR-multiview extension and SDK packages to accelerate direct rendering architecture compatible with Tile-Based Deferred Rendering GPUs:

- Spatial Culling: Equipping the engine with system spatial tracking data to enable early culling of geometric shapes outside the field of view using Frustum and Occlusion Culling.

- Cache Optimization: Minimizing unnecessary load and store operations between fast on-chip GMEM and main system LPDDR RAM via appropriate Vulkan instructions such as VK-ATTACHMENT-STORE-OP-DONT-CARE tied to lazy allocation memory properties like VK-MEMORY-PROPERTY-LAZILY-ALLOCATED-BIT to ensure data remains strictly within GMEM, provided it is technically verified that depth or stencil data is not needed in subsequent read passes within the same frame cycle.

D. Motion-Dynamic FFR and Viewport Stability

Advancing Dynamic FFR by introducing the Motion-Dynamic FFR mode, which links shading efficiency to actual GPU load as a primary metric, assisted by inertial motion sensors including IMU and Gyroscope as an active predictive factor:

- Sensitivity Tuning: Passing IMU readings through a temporal interpolation buffer with a precise sensitivity threshold to prevent visual shimmering or sudden shading grid pop due to sudden movements.

- During Rapid Head Turns: Dynamically increasing peripheral foveation levels and reducing edge shading resolution via Variable Rate Shading dynamically to alleviate load, accompanied by advanced edge smoothing filtering to prevent peripheral flickering.

OS PERFORMANCE PROFILES

Providing unified software interfaces allowing developers and users to choose standardized options compatible with system settings:

- Balanced Profile: Default profile maintaining a balance between resolution and screen refresh rate of 90Hz or 120Hz.

- Fidelity Profile: Targeting a higher rendering scale with complex geometric details at a 45 or 60 FPS processing rate visually doubled via AppSW.

- Competitive and Ultra-Low Latency Profile:

- Maximum priority given to responsiveness and a true, stable 120 FPS.

- Disabling AppSW and deep motion predictions to avoid the 1-frame latency penalty associated with synthetic generation.

- Relying on advanced synchronization technologies like Phase Sync and instantaneous reprojection or Timewarp, while reducing secondary effects.

NATIVE SYSTEM PERFORMANCE OVERLAY

Developing a real-time monitoring tool built into advanced system settings in Horizon OS based on original XR-PERF-SETTINGS interfaces as an expansion of OVR Metrics Tool functions:

The overlay HUD allows developers and users to read real-time CPU and GPU consumption, frame processing times, temperatures, memory usage, and bandwidth efficiency with zero-overhead OS overlay.

Conclusion Note: This document serves as a technical proposal derived from practical development and interaction experience with the Meta Quest ecosystem, aiming to share ideas on hardware utilization capabilities in Horizon OS and its accompanying SDKs, supporting the aspirations of the developer and user community across current and future generations.