Ray Tracing GI causes Emissive material not lighting up [HDRP]

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1

Hi, Im trying to create a scene using 2020.1.11f Unity HDRP. I made two emissive materials in the scene. When i assign SSGI volume to the scene with with ray tracing on, the mesh is not emitting light from its surface but the bounce light works just fine. As I turn off the ray tracing GI, the surface lit up but the bounce light is too subtle.

How do i fix this? Ive searched the internet for this problem but found no answer.

Here i attach screenshots of the scene:

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This is with Ray Tracing GI on

2560Ă—1440 612 KB

This is with SSGI without Ray Tracing

2

Emissive property on HDRP/Lit shader simply broken (or just not supported?) for ray tracing. HDRP/Unlit shader with emissive works fine, if unlit is enough for the purpose.

3

Hey, while it’s unexpected, nothing is broken, it’s just a consequence of the design.

You see, in deferred SSGI/RTGI share a buffer with emissive. So, unfortunately, having SSGI/RTGI ON in your scene will override your emissive contribution. This behavior was addressed in HDRP 11 & 12 (2021.1 2021.2) by adding a new Forward Emissive Pass that will render the emissive contribution in Forward. All you need to do for that is check the “Force Forward Emissive” checkbox at the bottom of the material property.
Keep in mind that it also performs an additional DrawCall. This means it uses more resources on your CPU.
Group of Materials / GameObject can be setup to use Force Emissive forward with the script “Edit/Render Pipeline/HD Render Pipeline/Force Forward Emissive on Material/Enable In Selection”.

If you are using HDRP 10 or below, there’s only two solutions left for you:

  • Uncheck receive SSR/SSGI on your emissive material, that way they won’t get SSGI/RTGI, so their emissive contribution won’t be overridden.
  • Use forward rendering (as we don’t have this buffer sharing in forward)

7224772--869095--force_forward_emissive.png

4

Works perfectly! It went according to the direction of the scene.

Which method is better for performance? simply change it to Unlit material or these two methods?

Thank you. All of the method solves my problem!

5

Depends on your needs for the scene. If you don’t care about lighting for these material, then HDRP/Unlit will be cheaper than HDRP/Lit for sure.
If you need lighting then better use HDRP/Lit with receive SSR/SSGI unchecked.

6

I had the same problem. The emission also works for me after I have deactivated “Receive SSR”. But the ray tracing Global Illumination and Ambient Occlsuion as well as Screen Space Reflection does not occur. Why?