Real-time ray tracing uses the same PBR maps as a path tracer, with a tighter budget. You get a handful of rays, a denoiser, and often a hybrid: raster for primary visibility, traces for reflections or GI. If you author materials as if you had 1024 samples and 8K on every prop, the viewport will be noisy, smeared, or both. This guide is the game- and viewport-side checklist.
Same BRDF, fewer rays
Unreal (Hardware RT, Lumen hybrids), Unity HDRP, and GPU viewports still expect metalness/roughness. Read the PBR textures guide for slots. What changes is noise. A roughness of 0.0 on a large floor traces a sharp, expensive reflection. A roughness map with 0.2–0.5 variation looks richer and denoises better. That is an art choice that also saves frames.
Keep IBL for the distant lighting. RT is not a reason to delete the HDRI. Combine them as in HDRI and PBR lighting.
Texture budgets that survive RT
RT needs the scene in memory plus acceleration structures. Oversized textures steal VRAM from that. Defaults that hold up:
- 2K for most props and walls. 1K for clutter. 4K only for a glossy hero the camera and the traces both see.
- Compress albedo with BC7 or ASTC; normals with BC5. Do not ship uncompressed PNG in a packaged game.
- Pack roughness, metalness, and AO so you sample fewer textures per ray.
Use the resolution guide before you enable 4K “because RT shows more detail.” RT shows more lighting, not a free resolution upgrade. Pull maps from the Locker3d catalog at the size you will bind.
Materials that denoise versus materials that crawl
Brushed metal with a real roughness map denoises into a stable streak. A flat 0.05 roughness chrome wall crawls as the denoiser chases a moving highlight. Tiled wood with a repeating shiny knot will appear in every reflected copy; break the repeat with a second UV or a cheap overlay.
Avoid metalness 0.5. Hybrid RT plus denoising turns that into a sparkling rim. Paint metals as 1 and dirt as a dielectric layer.
Engine-specific habits
In Unreal, set normal maps to the correct flip, use the default lit model, and do not enable every RT feature on day one. Reflections first, then GI, then shadows. In Unity HDRP, match the HDRI sky intensity to your exposure and watch the “smoothness” slider (it is inverted roughness). In Blender viewport RT or Cycles GPU, treat the viewport denoiser as lookdev only; confirm a still at higher samples before you call the material done.
Document DirectX versus OpenGL in the material folder. Real-time engines will not guess correctly for every imported PNG.
Ship checklist
- Lookdev under IBL without RT. Lock albedo ranges.
- Enable RT reflections. Walk a chrome sphere through the level.
- Cap roughness on huge mirrors unless the design needs them.
- Compress and downres. Confirm VRAM with RT on.
- License: Locker3d is free CC0 for commercial games. See CC0 can and cannot.
Offline path tracing and real-time RT share a material language. They do not share a sample budget. Author for the cheaper one if the project must run at 60. More notes are on the blog.
Frequently asked questions
Is real-time ray tracing different from offline path tracing for materials?
The BRDF is the same. Real-time RT uses fewer rays, denoisers, and hybrid raster for GI or reflections. Materials must be cheaper and cleaner: sane roughness, no mid metalness, and resolutions that fit VRAM.
What texture settings matter most for RT games?
Correct color space, BC5 or equivalent normals, roughness variation so mirrors are rare, and 2K as the default. Enable RT after the maps are clean; RT will not fix a baked albedo.
Can I use Locker3d textures in an RT title?
Yes. They are free CC0, so you can compress, downres, and ship them in a commercial game. Document DirectX versus OpenGL normals for your engine.