NvRTX_Caustics: Absorption (or how-to for coloured gemstones)

Gaming and Visualization Technologies Engines Unreal
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1

Hi there,

Trying to create coloured glass/gemstones with the (amazing) Caustics branch, I keep on running into this issue:

I’m creating colour in the material by absorption, as per the NVIDIA example scene, but to get the right colour intensity I need to dial up the Opacity. However, when it gets above a certain value it just renders black.

Here are examples with Opacity set to 0.5, 0.9, 0.97:

Screenshot 2023-09-12 100025
Screenshot 2023-09-12 100025814×710 89.2 KB

Screenshot 2023-09-12 100049
Screenshot 2023-09-12 100049702×668 76.4 KB

Screenshot 2023-09-12 100058
Screenshot 2023-09-12 100058814×730 89.3 KB

How might we work around this issue?

Cheers,
V

(it’s the same in the 5.1 branch and the 5.2 branch, which is why I didn’t specify a version)

2

Ok, got it:

Lowering “r.RayTracing.Translucency.MinRefractionThroughput” to 0.001 (default is 0.05) makes the black go away, but it does cost a few ms extra…

:)

3

Just use the simplest translucent material color and opacity value to control the fall off, e.g if you want a thick glass, just scale you glass model thickness, and then it will be less transmissive.