Dynamic Shadows not showing on Translucent Material

[mikesira]

Hello everybody,
we are completely lost.

we have a scene with a stationary sun, with both static and cascade shadows. Dynamic shadows start to appear when you are a distance of 350. In the scene we have a couple of big doors with windows on them. Opaque material is a normal white material and the translucent is the M_Glass provided in the default UE file.

The problem is the dynamic part of the light is not casting translucent shadows in game or in the viewport (cascade shadows not working with translucency). But when you select the Static Mesh in the viewport, the shadows appear. The static part of the light is working though, the static shadows are correct.

We have also tried with different meshes, and the problem persists. So we deduce is an issue with the light source, or the translucent material, but we can’t figure it out.

We attach some images of the scene. The double door is an actor blueprint, it’s set as movable and one of the windows has the option ‘Light as if static’ checked. The single window is a simple Static Mesh and is set as static.

Here you can see the mesh appears completely opaque, the translucent glass is not working at all. No matter if the Mesh is movable or static. Same with the translucent cube.

The static shadow is working correctly. You can see in the double door, that we window with the option ‘Light as if static’ is casting a static shadow.

You can see here the transition from cascade shadow to static shadow clearly happening.

When you click on the meshes in the Viewport, the dynamic shadows appear! It also happens when we have Show > Collision enabled.

Any ideas on what’s happening? We hope you could help us. Thanks in advance!

[Tim_Hobson]

Hi Mikesira,

Assuming that you have multiple materials setup for your mesh and the window material is it’s own material you will need to set the following things.

Material:
Blend Mode: Translucent
Two-Sided: True
Lighting Mode: Surface Translucency Volume

Then for your mesh placed in the level select it. In it’s Details Panel make sure that Volumetric Translucent Shadow is set to True.

This will cast a shadow from a translucent material, however the more opaque the material the more you’ll notice artifacts on the mesh itself.

Here is an example with a simple cube mesh and basic translucent material.

You may also notice that there is transmission of light (ie. color of the translucent object does not cast to the ground). This is not implemented currently and can only be done by using only static lighting

I hope this helps.

[mikesira]

Hi,
Thanks that was the correct solution to our problem
Cheers!

[anonymous_user_3e5d77691 (anonymous_user_3e5d7769)]

I do have a question, I noticed that there was a thing that says “hidden shadow” can I use that to make the object cast dynamic shadows while making the object not visible in game? or is there absolutely ANY way to make an invisible object cast a shadow?

[Tim_Hobson]

@Raxmo

Using the option for Cast Hidden Shadow will allow you to cast a shadow from a hidden object. So with that you can set in the Details Panel for the actor Visibile to False. This is for the Editor view, so it’s really up to you how you would like this to be set. For the second part you’ll set the Actor Hidden in Game to True. This means that even if you can see it in the editor it shouldn’t be visible in the game. If you’ve got the option for Cast Hidden Shadow enabled you’ll see only the shadow rendered.

I hope this helps.

[anonymous_user_3e5d77691 (anonymous_user_3e5d7769)]

I think so… but the real question is whether or not the hiden shadows can be dynamic shadows, and if so, what it would take to make that possible

[Tim_Hobson]

It supports dynamic and statically lit objects. There is no different setup than what was described in my previous post.

[anonymous_user_3e5d77691 (anonymous_user_3e5d7769)]

I did a little faffing about and it works! good god this is unsettling, this is perfect! thank you so much!

[Cundall77]

Hi , i need help fast! i’ve followed all the steps as above and it works fine, but the moment i build the lighting the shadows for the alpha disappear once more. I have attached images to show. the left tree is unbuilt lighting and the right is built lighting. Thank you!

[anonymous_user_14455c4f]

Hi , I added translucent shadow according your post. But the translucent shadow penetrates to object in front of the shadow caster. I tried changing mterial translucency 's lighting mode, only “Volumetric Directional” has improvements but not totally solve this problem. Any idea to fix this?