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Material that is translucent in only one direction?

Gus
Newcomer
I would like to model a lowered ceiling in an addition and I would like the material the ceiling is made of (in the model only) to be translucent from above and opaque (gyp. board) from below. Is this possible? Is there a material that will behave in this way, or is there a setting that will make this possible?
www.michaelgustavson.com Architect NY WI IL
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3 REPLIES 3

Gus wrote:
I would like to model a lowered ceiling in an addition and I would like the material the ceiling is made of (in the model only) to be translucent from above and opaque (gyp. board) from below. Is this possible? Is there a material that will behave in this way, or is there a setting that will make this possible?

Unless you're doing an animation, what view are you considering taking that will show both sides of the ceiling (top and bottom) at the same time?

And assuming you're not, then why not just use two separate materials that are view specific to the specific views you're rendering?

Alternatively, you could just model your ceiling object (I'm assuming it's a slab) to have 2 different materials (or surfaces;.... I just can't get used to referring to them as "surfaces" per Graphisoft's new nomenclature system after AC16) on either side of the slab - glass at the top and opaque at the bottom.

This may seem counter-intuitive but could actually work thanks to a little (necessary) logical quirk that most render engines tend to suffer from in simulating reflections and refractions known as "backfaces".

In real life, when an object is opaque on one side(or face) and "transparent" on the other (i.e like a glass pane that has an opaque coating on one face) then no light will get through either side as long as the opaque face is 100% opaque.

In the virtual world, this isn't necessarily the case because of the phenomenon of "backfaces" which basically refers to the face of the object that's always facing away from the camera in a closed object and which doesn't have any specified material definition (typically) which means that light can literally ignore what's happening on the other face facing away from you, or what it's supposed to do.

But this assumes that Cinerender treats backfaces like other renderers do (which is to say, it ignores them and treats them as non-existent rather than specifying the same material as the front-face. Some programs can do this (like Rhino3D) but it's not realistic or physically accurate since 2-dimensional objects and faces don't exist in our 3 dimensional world).

You can try it out and see if it works and you'll know right away, especially if you get weird results (like shadows on one side and none on the other, or shadows where there shouldn't be any)

Also, this is a little inside baseball stuff and more "science-y", (but really, high school physics level of science) explaining how it's treated in Cinerender and why it's important to have closed surfaces (which leads me to believe that backfaces are treated the same way in Cinerender as they are in other typical render engines) and might also help you understand how it works.

http://helpcenter.graphisoft.com/guides/archicad-18-int-reference-guide/user-interface-reference/dia...

Anonymous
Not applicable
Gus

In the 3D window when you use the OpenGL engine you can get the effect you're after.
Setting the plasterboard material to the bottom surface and say glass as the top works.
Unfortunately the 3D OpenGl is the only situation that occurs.
We have saved the 3D view out as .tiff and placed it in a worksheet
to create internal shadow diagrams on occasion!

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