Achieving realistic lighting and reflections in XR is challenging due to performance constraints, but modern techniques enable convincing results without sacrificing frame rates. Below is a breakdown of best practices, technologies, and optimizations for real-time reflections and lighting in VR, AR, and MR.
1. Real-Time Lighting Techniques
A. Dynamic vs. Baked Lighting
| Type | Pros | Cons | Best For |
|---|---|---|---|
| Baked (Lightmaps) | High quality, no runtime cost | No dynamic changes, large storage | Static scenes |
| Real-Time (Dynamic) | Responsive to changes | Expensive (shadows, GI) | Interactive XR |
| Mixed Lighting | Balances performance & realism | Requires setup | Most XR apps |
✅ Best Practice:
- Use baked lighting for static objects (walls, floors).
- Apply real-time lighting only where needed (moving objects, player-held lights).
B. Global Illumination (GI) in XR
- Lumen (Unreal Engine 5) – Dynamic GI, but heavy (best for PC VR).
- Light Probe Probes (Unity/Unreal) – Approximate indirect lighting.
- Screen-Space GI (SSGI) – Faster but limited to on-screen pixels.
C. Shadows in XR
- Hardware-accelerated shadows (Vulkan/Metal/D3D12).
- Optimization Tricks:
- Use cascaded shadow maps (CSM) for large scenes.
- Limit shadow distance (e.g., 20m in VR).
- Disable shadows on small/distant objects.
2. Real-Time Reflections
A. Reflection Methods Comparison
| Technique | Performance | Quality | Use Case |
|---|---|---|---|
| Screen-Space Reflections (SSR) | Fast | Medium (missing off-screen data) | Water, glossy floors |
| Planar Reflections | Expensive | High (mirrors, puddles) | Small reflective surfaces |
| Cubemaps (Baked/Real-Time) | Cheap | Low-Medium (static envs) | Metal, glass |
| Ray-Traced Reflections | Very Expensive | Ultra-realistic | High-end PC VR |
✅ Best Practices:
- Use SSR for dynamic scenes (Unity URP/HDRP, Unreal).
- Blend cubemaps with SSR for better coverage.
- Disable reflections on non-essential objects.
B. Reflection Probes (Unity/Unreal)
- Place probes strategically (near shiny objects).
- Update rate: Use “Every Frame” only for critical reflections.
C. Optimized Shaders for Reflections
- Roughness-based reflection blur (cheaper than real-time rays).
- Matcap shaders (fake reflections for stylized XR).
3. Platform-Specific Considerations
A. Mobile VR (Meta Quest, Pico)
- Avoid real-time shadows (use baked lighting).
- Use mobile-optimized SSR (Unity URP SSR).
- Low-resolution cubemaps (512×512 max).
B. PC VR (SteamVR, PSVR2)
- Dynamic lights + Lumen/RTX GI (if GPU allows).
- Ray-traced reflections (NVIDIA VRSS 2.0 supported).
C. AR (ARKit, ARCore, Vision Pro)
- Environment Probes (match real-world lighting).
- LiDAR-assisted reflections (Vision Pro’s RealityKit).
4. Performance Optimization Checklist
✔ Target 90 FPS+ (VR) / 60 FPS (AR).
✔ Use GPU instancing for repeated light sources.
✔ Reduce shadow resolution (1024×1024 → 512×512).
✔ Disable reflections on non-visible objects (occlusion culling).
5. Future Trends
- AI-upscaled reflections (DLSS/FSR for XR).
- Neural Radiance Fields (NeRF) – Real-world lighting reconstruction.
- Varjo’s foveated rendering (high-res reflections only where the eye looks).
Key Takeaways
- Bake what you can, optimize what you can’t.
- SSR + cubemaps = best balance for XR.
- Shadows & reflections are the biggest FPS killers—tweak carefully.