Lumen Compositing in Pixotope - Recommendations

Reflections

Hit Lighting for Reflections

• Recommended for better results, though more demanding

• PostProcessHandler > Lumen Reflections > Ray Lighting Mode

  • Enable "Use Hardware Ray Tracing when available" in Project Settings > Rendering > Lumen

When using a VS Internal Compositing plane and

• Hardware Raytracing is enabled

• Lumen is used for reflections

• Ray Lighting Mode is set to Hit Lighting for Reflection

• Max Refraction Bounces is above 0

• and its reflections are flickering

enable its "Disable Scene Capture Mesh" option. This disables a problematic submesh that interferes with virtual set reflections.

Max Refraction Bounces

• For VS, use 2+ bounces

• Use more if you have overlapping comp planes

• PostProcessHandler > Lumen Reflections > Max Refraction Bounces
  

  

Global Illumination

• When using Lumen for reflections, we recommend using it for Global Illumination as well

Skylight

• When using Lumen for Reflections and Global Illumination, include a Skylight in the level

No Sky in AR Reflections

• Enable this in Pixotope World Settings to avoid sky haloing around reflections

• This costs some performance

• Alternative: Use the erode setting (cheaper, but visually less appealing)

Adjusting Reflection Brightness

• If reflections are too dark, use the console command: r.Lumen.Reflections.SpecularScale

  • Try values between 1 and 8

• Especially useful if your materials have high roughness values

Raytraced Lumen GI for Dark Areas:

• Adjust culling settings to reduce small "flickers"

• More aggressive light culling can help

Shadows

• Shadows are generally easier to manage than reflections

• Pixotope World Settings for shadows should work as they do without Lumen

Learn more about Pixotope World Settings

Ambient occlusion

• With Lumen, ambient occlusion is part of the Global Illumination calculation, not a separate pass

• Material Ambient Occlusion can be enabled with Lumen for enhanced effect

Learn more about Material Ambient Occlusion → https://dev.epicgames.com/community/learning/tutorials/bOEy/material-ambient-occlusion-ao-in-unreal-engine-5

Lumen reflections - technical

Lumen uses at least three reflection "layers", each producing a

• reflection color (float3)

• hit distance (float)

  • representing distance from reflected object

  • distances are encoded as negative, positive means no hit

1. Screen Tracing

   • Similar to screen space reflections

   • Results in position of reflection and scene sample

2. Voxel Tracing

   • Not currently in use

3. Ray Tracing

   1. Surface Cache Ray Tracing

      • Produces a light/color atlas and samples it

      • More complex process

   2. Direct Ray Tracing

      • Simpler at its core

      • Works well in Pixotope and is recommended