Fabric behavior to light

Discussions regarding Materials, Material-Compounds or Shaders, etc.
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mc_axe
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Fabric behavior to light

Post by mc_axe » 31 Mar 2015, 20:23

Hello, hypothetically speaking, lets say that i want to create an image of a realistic sheet.
A sheet that just had been washed, so its hanging in a rope against sun, and its not ironed yet.

I noticed that im mising few things to achieve realism:

1)When the fabric is vertical against camera, or lets say between camera and sun -> fabric has max transparency.
When fabric has increased angles against the camera/sun , or when it goes like parallel , the fabric gets like zero transparency.
Image

2)Also i noticed that shadows casted on the front side *(to the side where the light falls) appear on the back side too .
But on a simple test i did thats not happening by default:
Image

How can i get these effects.
Just researching.

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mc_axe
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Re: Fabric behavior to light

Post by mc_axe » 01 Apr 2015, 13:00

Im most interested in the first question^^
And just to give you more info of what i mean, check this out:

Image

I painted this gradient by hand, so obviously is not correct, but you get the point.

Any ideas on how i can get a similar map to use it later as another layer of transparency, or smthing?

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rray
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Re: Fabric behavior to light

Post by rray » 01 Apr 2015, 14:04

Transparency effect could be done with an incidence node in transparency, set to camera incidence. The backside lighting effect has different names, depending on which renderer you use. Not all materials support this also. In mental ray standard phong material it's called translucency. It works only when your cloth is one polygon layer.
Softimage Resources section (formerly known as rray.de/xsi) updated Oct 01 2017

caledonian_tartan
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Re: Fabric behavior to light

Post by caledonian_tartan » 01 Apr 2015, 14:11

i also think its a case for the incidence node.
this quick test is without shadows or transparency.
inc.jpg
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mc_axe
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Re: Fabric behavior to light

Post by mc_axe » 01 Apr 2015, 15:54

Nice!

Thanks guys for answers. Ill make some tests!

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mc_axe
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Re: Fabric behavior to light

Post by mc_axe » 04 Apr 2015, 20:38

Round 1 of tests complete.
Just letting this tree over here just in case.
Image
Note*The last mix down and right is not necessary.

+Transulency works fine, and the shadows look impressive when appear in the back side too esp. soft Shadows/self shadows.
+Incidence works fine for the overall polygonal shape, and it has parameters so its quite handy and can simulate (the angular transparency) lots different types of cloths i guess.

-The bumps are wiped in the back faces, (shaded area).
-I cant get correct angular transparency for the fine details. Non ironed areas etc.

How can i convert a bump map or a normal map to something like incidence?

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FXDude
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Re: Fabric behavior to light

Post by FXDude » 10 Apr 2015, 05:49

That's pretty cool.

Also quite useful for drapes and the like and should be applicable to any renderer,

Thanks :ymcowboy: