hz-unity-code-review

Unity Code Review for Meta VR

When to Use

Use this skill when reviewing Unity C# code or project settings that target Meta VR headsets. This includes:

• Reviewing scripts for VR performance issues
• Checking rendering pipeline configuration and settings
• Ensuring adherence to Meta VR-specific best practices
• Identifying common VR development pitfalls
• Validating input handling for controllers, hands, and eye tracking
• Auditing memory usage and GC allocation patterns

Key Review Areas

1. Rendering Pipeline Configuration

Meta VR applications must use the Universal Render Pipeline (URP) with specific settings optimized for mobile VR. The Built-in Render Pipeline is not recommended for new Meta VR projects.

Critical settings to verify:

• Single-pass multiview must be enabled (Player Settings > XR Plug-in Management > Oculus > Stereo Rendering Mode)
• Vulkan should be the primary graphics API
• Linear color space is required for correct lighting
• HDR should be disabled in URP asset settings
• Post-processing should be minimal or disabled

2. Draw Call Budgets and Batching

Meta VR has draw call budgets that vary by workload complexity. Every draw call has CPU overhead that directly impacts frame timing.

Enable and verify:

• Static batching for non-moving geometry
• GPU instancing for repeated objects
• SRP batcher for URP materials
• Dynamic batching for small meshes (< 300 vertices)

3. Shader Complexity

Mobile GPUs on Meta VR cannot handle desktop-class shaders. Review all materials for:

• Use of URP/Lit or URP/Simple Lit instead of Standard shader
• Custom shaders that minimize texture samples and ALU operations
• Avoidance of real-time shadows where possible (bake instead)
• No screen-space effects (SSAO, SSR, screen-space shadows)

4. Memory Management

GC allocations cause frame hitches and must be eliminated from hot paths.

// BAD: Allocates every frame
void Update() {
    string label = "Score: " + score.ToString

5. Input Handling

Meta VR supports multiple input modalities. Code should handle:

• Controllers: Use Unity's Input System Package for new projects (recommended); OVRInput is maintained for legacy support
• Hand tracking: OVRHand and OVRSkeleton for hand pose data
• Eye tracking: OVREyeGaze (Quest Pro / Meta VR Glasses, requires permission)
• Graceful switching between controller and hand tracking modes

6. Physics Configuration

Physics simulation is expensive on mobile. Review for:

• Physics timestep set to match target frame rate (72/90/120 Hz)
• Simplified collision meshes (use primitives, not mesh colliders)
• Reduced solver iterations (4-6 is usually sufficient)
• Layer-based collision matrix to minimize pair checks
• Rigidbody sleep thresholds configured appropriately

7. Audio Setup

Audio is often overlooked but can impact performance:

• Compress audio clips (Vorbis for music, ADPCM for short SFX)
• Use streaming load type for clips longer than 1 second
• Limit simultaneous audio sources (target < 16)
• Spatialize audio using Meta's audio SDK for 3D positioning

Quick Review Checklist

What to Look For in Code

GC-Heavy Patterns

Update() Misuse

Camera.main Anti-Pattern

Find Calls in Hot Paths

Using metavr for Validation

You can use the metavr tool to validate builds and check device-side behavior. Invoke via metavr <args> (published as the npm package metavr; if metavr is not on PATH, run npx -y metavr <args>) — no install required.

Use device-side profiling to validate that code review findings translate to real performance improvements.

Reference Documents

For detailed guidance on specific topics, see the following reference documents:

• Performance Checklist — comprehensive performance targets and optimization strategies
• Rendering Best Practices — Meta VR-specific rendering configuration and shader guidelines
• Input Handling — controller, hand tracking, and eye tracking implementation
• Common Pitfalls — frequently encountered mistakes and their fixes