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Raytrace: Translucency Blocks Reflection

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    Raytrace: Translucency Blocks Reflection

    So I just discovered this. Attached to this post I have two images, one with a Raytraced reflection off of a floor, and another one with Screen Space. The Raytraced reflection is the one that is reflecting black screens on the monitors. And below I've written a description for what is happening. Lemme know what you think!

    I have a very glossy floor that is reflecting a wall with a mounted display. The mounted display has a screenshot for a texture of an AppleTV menu.

    And the glossy floor is reflecting the wall with the mounted display, however it is not reflecting the texture on the screen.And this is because the model I'm using has geometry for a sheet of glass in front of the screen with the AppleTV texture, and I created a simple transparent, but glossy, sheet of glass in front of the actual AppleTV textured mesh.

    I've discovered that raytraced reflections won't trace through glass materials. Dunno if this is something that is looking to be improved or if there's a current way to setup the raytracing settings to fix this, but I wanted to make a post about this.

    I have a workaround, but I would prefer that the raytrace reflection just work as expected if that's possible.

    Can confirm, that as soon, as you use translucent materials of any kind, they won´t be reflected. In fact, it seems, that none other than opaque surfaces will be reflected with Raytracing, at the moment... which is really bad for any kind of decals (especially, if you use nice parallax occlusion mapping decals ). Hope, that will be fixed/supported in 4.23, because you can see something in path tracing


      Thanks Suthriel! Yeah these are the early days of all this stuff in real-time. I'm sure eventually this will be a fixed/added feature. In my instance, I just got rid of the glass geometry and tweaked my screen material to also be reflective like glass for now, so it now reflects in the ray-traced reflections.

      It's a shame but I believe in these early days, interesting effects like translucency probably aren't fully supported in the ray-tracing side of things, and still will need to be worked around in more traditional methods.


        Has there been any progress on this front? A hidden setting maybe (like r.RayTracing.Reflections.ReflectionCaptures)? I've downloaded 4.24 preview 3 and the translucent meshes in ray traced reflections shader path still doesn't exist.

        If you have a mesh with ONLY translucent materials, the mesh will be completely hidden in ray traced reflections (for instance a window pane reflected in a mirror). However a mesh with MIXED materials (multiple slots with mixed translucent and opaque materials) will be shown COMPLETELY opaque, as if the translucent material is opaque in the reflection (for instance a framed shower door w/glass reflected in a mirror). I assume this was a conscious choice by the developers to try and make the most sense of the code paths that exist - just wondering if it's on the roadmap for development.

        Click image for larger version

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        Cameron Abt
        Atlas Bay VR

        Atlas Bay VR Logo


          I have a similar problem.

          My mirror does not show the background behind the window glass.

          Any solution to this?

          Click image for larger version

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            I actually have the opposite problem.
            I can't make material reflective unless they are translucent.
            So the windows are reflecting Ex&Interior but glossy metal box turns out total black.
            Any Ideas?

            Adrianork Have you tried to turn off the Cast ray traced shadow from the windows material? Or turning off the Shadows and Refraction from Ray Tracing Translucency tab in the Post Processing Volumn? This is wild Guess though.
            Edit: No it doesn't work.

            Seems like the only way to make it work is to use capture 2d the view(since the mirror won't move unlike character) and put it as emissive panel which is hidden in first pass in front of the actual windows. Seems like Epic bypassed the problem in the ArchVizSample by just not having windows at all! What a shame.
            Last edited by donglnapkrsskrss; 01-16-2020, 09:30 AM.


              The 4th method in my post will solve this problem but cause performance problem.
              The purpose of UE4 doesn't want to recurse in ray tracing.
              In my modify, actually you can set the parameters to fit your effect and performance.