Breadcrumbs

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

Screenshot 2024-10-11 at 14.21.40.png

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

    image-20240812-092227.png

Global Illumination

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

Screenshot 2024-10-11 at 14.23.33.png

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)

image-20240815-092548.png
image-20240815-092842.png
No sky in AR Reflections DISABLED
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No sky in AR Reflections ENABLED

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

UnrealEditor_Hmfj6ax6sM.png
Specular scale 1
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Specular scale 3

Raytraced Lumen GI for Dark Areas:

  • Adjust culling settings to reduce small "flickers"

  • More aggressive light culling can help

image-20240812-132614.png

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