Cast Shadows: Off -- not working with decals ?

Unity Engine
1

Hello.

Here is a simple situation – ground with dirt decal over it.
Lightmaps were computed both for ground and decal.
Casting shadows for the decal are disabled.
But as clearly visible on the screenshot – decal causes grave artifacts on the ground lightmap.
Looks like shadows from ‘Cutout’ material, but it’s not. Decal material Render Mode is ‘Fade’.
Again – casting shadows for decal are disabled.

Please check full-size image here https://i.ibb.co/JpqbNbP/Shadows-From-Decal.jpg

2

Synthetic test. White decal raised over the ground. What is that and how to fight such artifacts ?

3

Found answer here: the problem in Backface Tolerance parameter.

But the obvious solution via reducing the parameter solves decal problem, but it creates a lot of problems with black leaks. So, Backface Tolerance is not an option.

Next, I checked the dependence of black texels on the decal transparency. And I found a working solution - to set the decals transparency to the small value before lightmaps rendering, and return the original values after rendering.

Tell me please, is this what was intended?

4

Hey! You’ve ran into a really common issue. The reason why you are seeing those dark artifacts is due to invalid texels. They are invalidated due to all the backfaces of the plane that the rays are hitting. You can verify that yourself by baking the scene and switching to Texel Validity view. Invalid texels will be shown as red.

There are couple of ways to fix it:

  • Select your decal material, and check Enable Double Sided Global Illumination flag. This will treat the material as double sided for baking.

  • Uncheck lightmap static on your decal mesh, and instead have be lit by light probes. You will save on baking time and lightmap space this way. Keep in mind that you will need to build a light probe network first.

  • Use a custom lightmap parameters asset with a low backface tolerance parameter - something that you’ve already discovered. This will let rays pass through the object regardless of how many backfaces the texel sees.

I hope this helps.

5

Thanks, I’ll check it

6

It’s very funny but seems Double Sided GI flag is not suitable for decals.

On the screenshot – decal was lifted after baking lightmaps. You can see the shadow under it.
The most incredible fact – this shadow present on the lightmap, while Sun is mixed light source !!!

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