I learned in this thread that you can use Scene Color with Translucent Materials. Can Refraction operate on colour channels separately? - Rendering - Unreal Engine Forums
So with the blurred glass materials I took a similar approach to the Radial Blur Post Process effect. With this what is needed is something like a gaussian blur, so I just picked some samples around the pixel that was processed calculated a weighted average. Samples that are close to the UV coordinate have more weight than samples that are far away. The one in the picture doesn’t use a lot of samples, that’s why you can see those strange circles in it.
If you want to make it perfect you would need to use the TexelSize to make it pixel-perfect and pick all pixels in a radius (depending on how blurry you want it) around the UV coordinate.
This is what you can do in the material editor.
If you want a more efficient method you would probably implement a custom shader or shader node with HLSL and C++ directly for the renderer, afaik. If you do that you can make use of some faster blur/low pass filter algorithms.
For the Radial blur Post Process I didn’t really care, because there will only be one on the screen and I didn’t notice a significant drop in framerate even with more complex versions of it. The samples are also just taken in a line and not a circle, that means that less iterations per pixel are needed.
The other problem with the blurred glass material that I can’t solve is that I have to use the emissive output of the material. This means that any shading on the glass would not be visible. So I have put it on hold for now as I have to concetrate on more important tasks. I also don’t have ideas how to solve this problem. This might also require some modifications to the renderer.
As said in one of the posts above, this isn’t really my field, so there might be someone smarter than me in this area, who knows better.