Refraction in "unlit" view mode displayed incorrectly
The "refraction" parameter causing material to render incorrectly in "unlit" mode.
This image should explain the issue and provide all necessary information to reproduce the bug:
asked Dec 07 '17 at 12:30 PM in Rendering
Based on your original post, you mentioned was that your glass-like Material isn't rendering properly under Unlit mode in the viewport. That's possibly a bug, I'll grant you; we'll add a bug for it on our end. I wouldn't go so far as to say it's intentional, but there as a greater-than-zero chance that it's one of those things that isn't super high priority to fix, frankly speaking. Reason being that Unlit mode is more of a diagnostic tool than anything else, and not all rendering features are going to be supported within it.
Now, if your immediate response was, "But hey, I was making a game without lighting! Shouldn't I be using Unlit mode?" Then my answer would be, "No, not really."
You'd just make a bunch of Unlit Materials (set their Shading Model to Unlit) and use the regular Lit viewport. The Lit mode is utilizing UE4's full renderer, instead of just a portion of it.
Generally, we recommend you use Unlit mode only to diagnose specific issues. For example, say you're lighting your scene and can't tell if a particular rendering error is some aspect of your Material or how the shadows are falling across the surface. You would then switch to Unlit, and if you still see the problem, you know it's the Material. Make sense?
Now, if you were having difficulty creating the effect you described (and maybe you weren't... I'll try not to assume), then let's take quick look at it. It seems you're trying to do an Unlit translucent material and see the result of the Fresnel on the surface, rather than inside the refraction. The "hollow" effect you're seeing is due to the order in which the render - specifically the refraction - takes place. You want the refraction to happen in a different order to avoid the "hollow issue," so you should activate Render after DOF. This was formerly known as Separate Translucency.
If you do that, and set the Blend mode of the material to Unlit, (and plug your Fresnel into Emissive because in your screenshot you have it plugged into Base Color), then you get this:
So this has the white emissive Fresnel effect on the outside of the surface, not retracted in. That's the effect you were chasing, yes?
Now, that will still break in Unlit mode, as you've described. Most likely reason is that Render After DOF isn't supported in that mode. Again, think of Unlit mode as a diagnostic tool, not how you should be rendering your final project/game/etc.
Anyway, sorry for carrying on. This thread seemed like it was spiraling a bit, so I figured a more thorough explanation might help sort things out. Sorry for any inconvenience in terms of the view mode not working the way you'd like, and further for any communication issues in digging through your problem.
Have a nice day, and Happy New Year!
Refraction in the Unreal Engine is an approximation of the lighting phenomena that occurs when light passes from one medium to another, like from air to water. I am not sure why you would care about its appearance in Unlit mode, but it's working as intended.
Follow this question
Once you sign in you will be able to subscribe for any updates here