URP lit shader will not receive shadows while transparency is enabled

for me unity3d team think that who use unity is really stupid. they create bugs at each version and until using unity 2021 this problem is not solved. i try even amplify shader (that i buy on asset store with real money..) so this is only a unity question. they do with URP what they done with UNET, its only a big fake, otherwise, who don't need shadows on trasparent objects?

 

Didn't work for me unfortunately. I also tried to change that line of code in the package and Unity apparently rebuilt the thing, removing the changes I made.

 

This bug is still present for me in Unity 2021.2.0f1
Is this a shader issue or a built in Unity graphics issue?
Are there any fixes or workarounds?

 

just use surface type: opaque with alpha clipping, fixed for me

 

Are there some repro steps for this to break on recent Unity versions? I tried this on 2021.3's URP using it's own Lit - transparent and also using Lit SG and I always got shadows on transparent materials.

 

For shadows to appear on transparent objects, assign a URP Asset in the Quality Settings and use the Universal Render Pipeline/Lit or Simple Lit shader with Surface Type set to Transparent. If you don't have the URP assets assigned and you're just using the Standard shader you won't get any shadows.

 

I have a custom URP Opaque shader that received shadows fine in Unity 2019 and now does not in Unity 2021.3, is there something changed in the shader libs for that case ?

EDIT:

I found the cause, in the below code seems defaults to the second line than the first, seems _MAIN_LIGHT_SHADOWS fails to register or something, even though i have it in multi compile etc

Code (csharp):

1.  
2. #if _MAIN_LIGHT_SHADOWS
3.                 mainLight = GetMainLight(TransformWorldToShadowCoord(positionWS));
4. #else
5.                 mainLight = GetMainLight();
6. #endif
7.  

Is there something i am missing ? If i use the below code works

Code (csharp):

1.  
2. #if _MAIN_LIGHT_SHADOWS
3.                 mainLight = GetMainLight(TransformWorldToShadowCoord(positionWS));
4. #else
5.                 mainLight = GetMainLight(TransformWorldToShadowCoord(positionWS));
6. #endif
7.  

 

you can copy Lit shader and C# ShaderGUI (LitShader and LitDetailGUI , change namespace youself)
and change copied LitShader function
public override void ValidateMaterial(Material material)
{
SetMaterialKeywords(material, LitGUI.SetMaterialKeywords, LitShaderDetailGUI.SetMaterialKeywords);
material.SetShaderPassEnabled("ShadowCaster", true);
}
and change copied Lit shader
CustomEditor " your shader gui nameapce.name"

and you can don't have to change the source code frequently


urp author seems to think transparent objects shouldn't create shadows. That's the code he wrote

// Cast Shadows
bool castShadows = true;
if (material.HasProperty(Property.CastShadows))
{
castShadows = (material.GetFloat(Property.CastShadows) != 0.0f);
}
else
{
if (isShaderGraph)
{
// Lit.shadergraph or Unlit.shadergraph, but no material control defined
// enable the pass in the material, so shader can decide...
castShadows = true;
}
else
{
// Lit.shader or Unlit.shader -- set based on transparency
castShadows = Rendering.Universal.ShaderGUI.LitGUI.IsOpaque(material);
}
}
material.SetShaderPassEnabled("ShadowCaster", castShadows);

 

Hi, some keywords have changed in 2021.2, see this thread.

You can replace:

#if _MAIN_LIGHT_SHADOWS

With this:

#if defined(_MAIN_LIGHT_SHADOWS) || defined(_MAIN_LIGHT_SHADOWS_CASCADE) || defined(_MAIN_LIGHT_SHADOWS_SCREEN)

By the way, we can disable main light shadow in URP, so maybe adding another keyword:

&& !defined(_RECEIVE_SHADOWS_OFF)

Or replace with this (the same with URP's Lit shader):

#if defined(MAIN_LIGHT_CALCULATE_SHADOWS)

"MAIN_LIGHT_CALCULATE_SHADOWS" will be defined somewhere (*.hlsl) when the shadow is enabled.

Don't forget to change the pragma:

#pragma multi_compile _ _MAIN_LIGHT_SHADOWS _MAIN_LIGHT_SHADOWS_CASCADE _MAIN_LIGHT_SHADOWS_SCREEN

 

Thanks, very useful

 

Thanks for the clear explanation! Finally it casts shadows!

 

Solved with this!
Thank you very much!

 

The issue with this is that is no longer true transparent item, so will have more hard edges borders, i suppose could use 2 different passes, one for color with true transparency and one for shadow with the cutoff.

 

Any fixes for this? The code change doesn't work anymore. It's no longer true or false, and they seem to imply that there's a "castshadow" checkbox in the Lit material (there isn't). Even if you want to force it to true, you can't cause it gets reverted immediatly on save.

I have a meterial that needs to "fade" out, and the shadow fades out with it.

 

This is still happening with URP v14.0.8 on Unity 2022.3.6f1 LTS
is there any workaround to make an object fade?

 

Same issue

 

as far as I know
receiving shadows on transparent objects: not a problem, as pointed to above activate that on the urp asset
casting shadows from transparent objects if the shadow can be fully opaque: again easy, a custom shadergraph without any major changes has that Cast Shadow toggle.

Now Fading Shadows from the receiving end (aka fading all shadows on an object) easy as well if you are willing write the lighting code yourself.

But Fading Shadows from the casting end... very difficult. Look at the URP .shader files. All shaders have a shadowcaster pass which write a fragments depth value into the current rendertarget, the current rendertarget at that moment being the shadow map. A depth value can not be faded, it can only be blended but that is not 50% shadow on that pixel but rather a different position for the shadow.
Your best chance to get this imo is dithering the shadow caster. You want the shader to support alpha clipping but keep the clip value at 1 in the base pass and only in the shadow caster pass do the alpha clipping. Which can be done with a custom function node in shadergraph

something like this

Code (CSharp):

1. #ifdef SHADERPASS_SHADOWCASTER
2. alpha = someInputDitherPattern;
3. alphaClip = fadeValue;
4. #else
5. alpha = fadeValue;
6. alphaClip = 1;
7. #endif