Glass Material: Raytracing Translucency?

Hi Nilson!

appreciate it. I was running another quick test. In this Video I compare the Unreal Raytracer vs. the Vray Raytracer.

I followed the Unreal documentation to create a Glass Material with Refraction.
The result… unfortunately… does not work.

Watch here a short 4k Video with Audio Documentation, highlighting this major problem:

Following your messages:
Does this mean, that refraction just doesn’t work at all until the new Release of 4.23 is coming?

Source to the Unreal Documentation of the Glass Refraction Material.

That documentation you pointed out is currently the material setup for the rasterized method (UE4.21 and earlier) and so far that one works (sort of) for glass. My material setups I usually put a fresnel node going to Opacity and if the glass should show the inner side, I use double sided material, so I can fake thickness. More thickness to glass, above 1mm, would require a mesh like you described earlier, having an inner mesh with normals respecting the surface continuation from outside.

My expectation is that 4.23 with the adjustments in the translucency we can rely on the same material method used for rasterized or have anything extra in the settings to make it like the other renderers work such as VRay.

Is it possible to download somewhere a material/shader you mentioned, that works for refraction when using raytracing?
I am having the same issues… I can’t create get a glass material that works when using raytracing for the translucency.

The link is in the documentation as he stated here:, but it won’t work for all cases in Raytracing because the feature is under development, since the realtime raytracing feature is still in early access, and you can expect the next release to have the issue with translucency behaving as expected and also we will know if the feature will require material adjustments or if the way it is in the documentation will work out of the box.

I see. I guess all we can do for now is waiting. Thank you!

He there,
I’m on 4.23 and the problem is still there. can you confirm that ?

Not working yet, translucency is still work in progress in relation to realtime raytracing. Also, translucent materials won’t appear in reflections and the shadows from the meshes using them is solid black.

The IOR doesn’t seem correct to me either, it’s not changing at all when I adjust it.

Yeah, not being able to adjust the IOR is super annoying.

With the latest Release of 4.23 it’s working. I created a Video Tutorial for it. If you follow the steps, you should be able to get the same results shown in my video.

all details can be found here:

My Final Result:

My Video Tutorial:

I hope that helps - happy ray tracing!
cheers :slight_smile:

@BernhardRieder AFAIK you are still not able to see translucent materials reflected on other surfaces and those are also showing solid black shadows in reflections, so translucency still broken in several scenarios in 4.23.

the tutorial is informative. The glass material is really great with Ray Traced Translucency on, but the RT T Refraction is still off.
Cannot find nothing on how to properly use RTTR yet, specially geometries that are slightly more complex!!1136573952.jpg

do you have a model like that? I would like to run some more tests…

I followed Fatty Bulls walkthrough and I still get black windows. The window meshes are double sided, 5mm thick and I’m using 4.24P3. and the glass material is from the UE automotive materials pack. Any ideas as to what I’m obviously doing wrong would be super.

Thanks in advance.

There’s a few things to take into consideration for this to work. To make it simpler, here’s my master material, and it’s instance’s parameters below. Make sure the material blend mode is translucent, and the material’s lighting mode is set to Surface ForwardShading.

No need to change camera parameters like in the video above, you can do it for the whole scene in the post process volume. The main two settings you need to have are translucency type - ray tracing, and refraction - off.

Cool car btw :wink:

@JoshKitney if after the settings above you are still getting black windows, the reason is because it is double sided, so you will want to experiment Max. Refraction Rays with higher values, but the best would be if the mesh wasn’t double sided, because I am not sure how the light bounces are being dealt in that such small area… it might be black because it is reflecting the car interior and the bounces are not enough to get through the windows. Refraction Rays increase will cost, so if you are looking for cinematic it is ok.

Thanks @Bleen0_0 and @NilsonLima. I was experimenting again today and I got the result (attached). I also followed your steps just to make sure I was doing it right. Thanks for taking the time to write out your adventures.


Looks pretty awesome @JoshKitney ! Congratz !

Thanks mate. I’m still blocking out this guy, but I thought I’d do the glass first and not cry over my keyboard after doing everything, and then do the glass.

Those car windows look crystal clear, if you followed Bleen’s advice you should have opacity of .5.

I don’t understand. :frowning:

I just want clear glass with nice reflections, but I can’t seem to get it!