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[URP] Eliminate Dark Patches from Adaptive Probe Volumes

Solution

lightingrenderinggraphicsurpoptimization

Unity 2022.2.x - Unity 6.3.x

Published Sun, Mar 15

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Reviewed by _architect

Chief Editor

80 posts
Issue

 Unexplained dark patches appear on Mesh surfaces, specifically on bright horizontal areas like ceilings, when using Adaptive Probe Volumes (APV) for Global Illumination in the Universal Render Pipeline. Even when the Rendering Debugger indicates that all contributing probes are valid, these visual artifacts persist. Typical troubleshooting steps, such as modifying Normal Bias or adjusting the Probe Volume density, often fail to eliminate the shading errors in your scene.

Explanation

The observed dark patches in your project utilizing Adaptive Probe Volumes have been identified as a confirmed bug within Unity 6000.2.6f2 and URP 17.2.0. This issue stems from a defect in how the engine handles probe interpolation on flat surfaces.

  1. Open the Lighting window and ensure the Global Illumination mode is correctly set to Adaptive Probe Volumes.
  2. Create a Probe Adjustment Volume to identify and manually invalidate probes that may be sampling data from inside your geometry.
  3. In the Probe Volume settings, try increasing the Min Probe Distance to prevent probes from being placed too close to your mesh surfaces.
  4. If visual fidelity remains compromised, consider using Lightmaps as a temporary fallback for your project to ensure stable baked indirect lighting.

Additional Tips:

  • Check that the Dilation settings in your Adaptive Probe Volumes configuration are not pushing dark data into open areas.
  • Ensure that your geometry does not have back-facing normals in areas where Adaptive Probe Volumes are sampling, as this can confuse the interpolation logic.
  • Monitor the official Unity Issue Tracker for updates regarding fix version 6000.3.x.

TL;DR

Dark patches appearing in Universal Render Pipeline scenes using Adaptive Probe Volumes are a confirmed engine-level bug affecting Unity 6 (6000.2.6f2) and URP 17.2.0.


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Content inspired by a Unity discussion post.