Access Lumen reflection for manipulation in material?

In a Lumen scene, is there a way to access the reflection (not the reflection vector, but the reflected image itself) in a material?

My idea is that I’m creating a glass window as cheap as I can, and to make it look double-paned, it would be nice if I could double the reflection and use a BumpOffset to make it look like it’s from a second pane of glass behind the first.

If I’m to understand what you’re saying, you’re looking to grab the final lumen reflections pass, put it into a render target, pass that to a material and have the material display it?

The fundamental question is what you consider ‘the reflected image’. Because for most lumen reflections, rays are spawned on the Gbuffer, so radiance is gathered to screen-space. Furthermore, lumen handles translucent reflections via a special depth-peeling operation that is hardcoded to one layer of translucency (to my knowledge), so how you’d create a lighting model/HLSL to facilitate passing that information to the behind plane would be a trick.

My gut tells me that pulling reflection buffer information from the screen and reprojecting it onto a texture in world-space (if that’s what you’re talking about, I’m almost certainly misunderstanding), could break in a number of ways, not to mention what stage in the pipeline you’re doing this, as lumen goes through various denoising and accumulation passes.

By and large, ‘lumen’ and ‘cheap’ don’t normally go together in the same sentence. It’s a complex system that isn’t super accommodating to modification/weird lighting shader trickery, so I can’t help but wonder if a thin translucent material might do the trick.

Lumen does support multiple layers of translucent reflection, but every layer after the first uses the rather leaky and low-res radiance cache.