As a newbie, I’m a bit confused by transparent materials. As we always only work with (infinitesimally) thin mesh faces and normals, and never define any “volumes”, I get confused here.
With nontransparent materials like a concrete wall, the infinitesimally thin face is not an issue (well, as long as I don’t look at it from the side ).
But liquids, glass sheets etc are transparent, so I have to deal with their thickness to model something proper if the camera is close enough to take note or if it shall be physically correct? If I model a proper Window, I can’t just have 1 face of glass, no? I would need two faces, close together to correctly model the double refraction from air-[other medium]-air?
Or do renderers already do double refraction with just one face if I want to?
I’m rather confused by this flat surface vs. volume thing and where normals have to be pointed at etc.
EDIT: I just realised that I only assumed you were talking about Cycles… Did you? If not, forget my post right away…
Well, you can use flat planes for architectural glass, but I wouldn’t use the glass shader then, but rather a mixture of transparent/glossy (refraction on windows is negligible anyway, you want it to reflect a bit and let the light in…).
From my experience the glass shader indeed needs thickness to work properly. If Cycles is supposed to calculate a physically plausible image of light passing through transparent objects, your modeling has to be physically plausible, too. And that flat plane is - correctly speaking - not infinitesimally thin, but has no backside at all, which is not only implausible, but physically impossible… So, I always model glass objects like they are built in real life and furthermore to real life scale.
Just think of the following example: A solid glass ball vs. a hollow glass ball - how would Cycles know the difference, if you don’t model the inside in?
Yes, how would it know … so the outside sphere has all normals going out, the inside ball ll normals pointing inwards?
For Transparancy, does the normal matter? Say I have modelled a room … a simple cube. The camera is inside, all wall normals point inwards. Now I make windows. Outside the cube, I have a large plane with a glowing texture emision with a picture of space/planets etc to simulate an outside of a spacestation. Of course this outside picture has to be shown from inside the room through the windows and it should emit faint light into the room through the windows. What do I do with the “glass” of the windows? Simple faces, normal pointing inward as well like the walls? With like you say transparency/reflection? Or does something funky happen, if the outside light is hitting the window “glass” outside, when it’s normal points inward? Or does that not matter, since my camera is inside?
PS: Rendering used is Octane … not Cycles … but I will atm assume it is similar to cycles. It’s also node based and offer some similar nodes.
You usually can’t see the double reflection effect from bigger distance so it is not worth making the window glass thick. In archivis it is common to use so called architecture glass - in cycles you can use simple mix of transparent and glossy shader. If your windows have the thickness you need to increase the render bounces and the render time increases…
Oh, crap. I just saw your edit concerning Octane. Anyway, here’s the Cycles solution…
Your box example, all normals pointing inward, except for the right hand window, which has the normals pointing outward. As you can see, no difference at all: Light comes in, glowing ball is reflected, HDRI outside is visible. Also attached is the node setup for the “glass” material.
Hmmm. I only have Octane standalone here, so I don’t know what the exporter plugin can do. But if I just take the OBJ of the room into Octane, there actually is a difference from the normal orientation. See how the horizon line makes a sudden jump from left to right?
Never got the hang of Octane, actually. So maybe there is some trick to get architectural glass without hitches?
EDIT: Found it - you have to turn the IOR to 1.0, but you seem to loose the reflections, then.
Yes … I just realized that as well … my outside planet was repeated on the windows when the “Index” of the glossy node of the fake “architectural glass” is set to 1 … I have the same as you of course now … at 1 the planet shows right,but the inside light reflections are gone.
Octane feels similar to cycles to me … with the blender plugin, it’s just the same … arrange and connect your nodes etc. Rendering acts different, though
Don’t let the similar user interface fool you: Every renderer is a different beast and needs to be tamed in a different way…
So Octane glass obviously needs thickness and “Fake Shadows” enabled…
Hm … I set the Specular Material node index to 1 and activated the fake shadows … doe snothing for me (renders planet right, but no reflections). What thickness do you mean?
I extruded the glass polygons to give it “real” thickness.
Then I applied a specular material with an IOR of 1.5. With thickness the windows will let in much less light than before, so you need “Fake Shadows” to counter that.
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