I made a basic refraction glass material, following the example in UE4 documentation (fresnel, lerp between 1 and 1.5, normal map).
I put it on a plane.
I put Robert the Robot near my plane and I get this:
As you can see, the robot’s silhouette is drawing, duplicated, on the panel, disturbing refraction.
Same thing if I disconnect the normal map.
Same thing if I try to tweak parameters (IOR, fresnel node parameters, any parameter on the material).
The nearer meshes are from the plane, the stronger the artifact is.
I suppose it’s a well known problem but is there a way to get rid of this?
Yes, good catch!
I’ve seen this video but didn’t notice it.
Depending on how you use refraction, it can be a brief artifact, like in this shot
and then it’s not really a problem. The player doesn’t care.
The picture of the Kite demo shows a different problem than what EdWasHere described. It’s a limitation of the screen space reflection technique and has nothing to do with refraction. Unfortunately there is no way around it as of now.
Yes, in fact, i think that’s it. Refraction is not exactly disturbed this way, actors in front of a refractive surface don’t add color. At least, I never noticed such a thing.
@ ExpMini:
What if you increase the FOV (or decrease? I don’t know. I mean zooming a bit) to exclude these borders? Is it “FOV independant”?
I was asking about these refraction artifacts because, extending the possible uses of a post process material i’m working on to fake a blurring glass material, I found out that I could use it
to remove them. But as my setup is a bit expensive in terms of performance cost, I was wondering if you could make it in a simpler and cheaper way.
I’m struggling to progress with my VR project for the same reason and I can’t find anything online, I’d like to know why objects in front of a refracted surface are getting distorted by the refraction bellow, it’s ruining the experience and I’m starting to lose hope
I believe this is because refraction in UE is a screen space effect. This problem occurs with screen space reflections as well. I’d love to fix this too, perhaps doing some trickery with a depth pass can help but I have no idea how to approach this. Please let me know if you find something that helps!
The fix is to use raytraced refraction. It’s a limitation of screen space techniques. The refracted ray hit a spot where there is no background information because it is obscured by a foreground object. You can also use cubemaps to fake refraction but that has its own issues although it doesn’t have this problem.
