Corona 4 and absorption color

[Deckard]

Hi all,

I installed Corona 4 today and after opening a previous kitchen scene with two oil/vinegar bottles, the liquids inside them render as transparent. The liquids use an absorption color and a distance of about 5cm. Changing the distance value doesn't seem to fix it.

Any ideas? Something to do with the new caustics, I suppose?

Thank you.

[TomG]

Probably not the new caustics, unless you enabled them they will have no effect.

More likely is the overlapping media change. You should have been prompted on open to use the new functionality or the old - I'd try opening the scene, and selecting to use the old functionality, and see if that makes it render as it did before.

[Deckard]

Thanks for your reply. Yes, I could indeed try the old functionality and it could probably be fixed, but the question is: How does absorption in liquids work in corona 4? I tried creating a new material and applying absorption, but it still comes out transparent...

[TomG]

Absorption shouldn't have changed at all. What has changed is what happens when materials with refraction overlap - do your liquids render with absorption as expected when they are the only object in the scene and are not overlapping/intersecting anything else?

PS - some renders would help, and even perhaps the scene, if this is happening in, say, a simple test scene with a sphere.

[Deckard]

It was indeed an object overlapping issue. I scaled down the liquids slightly (so that they don't touch the clear glass bottles) and now they render fine.

Thanks for your help!

[romullus]

I scaled down the liquids slightly (so that they don't touch the clear glass bottles) and now they render fine.

But that is a wrong setup. Now your liquid probably is rendering incorrect. Liquid should overlap with glass container to render correctly.

[romullus]

I'm attaching quick renders to show what i mean. See how liquid in non overlapping renders look wrong.

[maru]

The liquid object SHOULD overlap with the container geometry, BUT you have to remember about correct normals direction. Since Corona 4 volumetric effects (absorption, scattering, refraction,...) are now dependent on normal direction. So if the normals of your glass and/or liquid objects are flipped, they won't render correctly.
See this for info on correct setup in V4: https://coronarenderer.freshdesk.com/support/solutions/articles/5000515618

[Deckard]

Thank you romullus and maru for your input, I appreciate it.
I wonder if there will ever come a day when CG software won't need these "cheats" anymore... (sigh)

[maru]

I wonder if there will ever come a day when CG software won't need these "cheats" anymore... (sigh)

At least Corona took one step forward in this regard. :)