does curtains need to have thickness?

[karklinskarlis1993]

hello there,

i wish there was a spam part of this forum as my question is really straight forwarded.
i made a few tests and onesided cloth looked imho a bit better than solid twosided. (onesided allowed more light to penetrate)

can anybody give me a fast hint what to do and how they do it. i am bit confused. its first time ever i use transparent curtains...





TWO SIDED <----> ONE SIDED

[maru]

You can use translucency on geometry with and without thickness. The results will be slightly different. Translucency is basically simulating very thin layer which scatters light.

With just one face on it's way, light will hit the surface, scatter inside of the very thin layer, and then pass to the other side.
With two faces, this will happen in two "layers", so the result will be probably a bit more "blurry", and less bright.

If you imagine a sharp shadow cast on such surface, with just one face, the shadow will be still sharp on the other side (imagine a sheet of paper). With two faces, it will get more blurry on the other side (imagine two sheets of paper, one placed behind each other).

Update: added a simple test to back up my theory. ;)

[karklinskarlis1993]

thanks for respond
so basically you can do it onesided way and dont get any weird artefacts coming from that am i right?
my aim is realism and in the same time ability to more light coming in as corresponding room has low amount of windows

[maru]

so basically you can do it onesided way and dont get any weird artefacts coming from that am i right?

Yes, there won't be any artifacts, as translucency is designed exactly for cases like this.

my aim is realism and in the same time ability to more light coming in as corresponding room has low amount of windows

Using curtains with no thickness will definitely not add realism, as there are no objects with no thickness in real life, so if you would like to have curtains with thickness, and bright interior at the same time, you can use the rayswitch material or map. For example you can use opacity-mapped material for the GI, and translucency for direct visibility: https://coronarenderer.freshdesk.com/support/solutions/articles/5000529341

[karklinskarlis1993]

got you. thanks a lot for your time, its much clearer now!