Author Topic: Doble-sided material  (Read 13271 times)

2014-04-29, 11:06:28

Juzwa

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Hi,

Since corona doesn't support any double-sided materials, how can I  acheeve a similar effect?

I have an animated book, flipping the pages. I need the pages to have different texture on both sides. Tried with shell mofifier, and assigning new materal to new faces, but however id doesn't work (even i scanline, i think its  just an unfinished and bugged feature).

So how can i render out double-sided materials in corona?

2014-04-29, 11:26:45
Reply #1

Ludvik Koutny

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Double sided map? :) It's called CoronaFrontBackMap. And if you instance the frontback map also to translucency slot, and give your paper material some translucency, then you will see the text on the other side of the page slightly leaking through when you look at the page against light source... like in real world ;)

2014-04-29, 12:11:47
Reply #2

maru

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Tried with shell mofifier, and assigning new materal to new faces, but however id doesn't work (even i scanline, i think its  just an unfinished and bugged feature).
What? If you make a plane and assign shell modifier to it, in shell options you have possibility to assign different material IDs to your new faces (inner, outer, side). This HAS TO work in both Corona and scanline. It's not a bug, it's unskilfulness. :P

For flipping pages, I would probably use geometry with thickness. But like Rawalanche said, using single-sided geometry with translucency could also bring nice effects.

2014-04-29, 12:56:12
Reply #3

Tanakov

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Not know how to do something, calling it bugged.. well You sound inpatient.

Do you get angry a lot?

Shell is the best option here, theres also an option with alphamapping and AE, but thats the least efficient way.
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2014-04-29, 13:10:10
Reply #4

Ludvik Koutny

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Not know how to do something, calling it bugged.. well You sound inpatient.

Do you get angry a lot?

Shell is the best option here, theres also an option with alphamapping and AE, but thats the least efficient way.

Shell is not really best option for something like book pages... And the guy does not sound angry...  he seems normally polite...

2014-04-29, 13:34:46
Reply #5

Ondra

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Tanakov, maru: hey, there is no reason to get personal!
Rendering is magic.
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2014-04-29, 14:15:55
Reply #6

Tanakov

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Tanakov, maru: hey, there is no reason to get personal!

Yes Master, I apologize to OP, yet I didnt realize that was mean.

Well I will stand with shell, as It can allow user to get some nice lookin closeups.
But I generaly realize there are better WF's.
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2014-04-29, 14:57:17
Reply #7

Juraj

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Not know how to do something, calling it bugged.. well You sound inpatient.
Do you get angry a lot?

This is the weirdest language barrier effect I have yet seen.



Shell is the best option here, theres also an option with alphamapping and AE, but thats the least efficient way.

Most book papers use 80g/m2 or less for pages, the thickness is literally irrepresentable with physical units in CGI, because it's sub <0.1mm. Sure, carton boards (400+ g/m2) are different league.
Regardless, thick papers would be nightmare to animate in flipping fashion.

Rawalanche's advice is sound. Still, 2sided material is convenient way to have completely different material characteristic on each side, but, not any sort of priority for anyone I guess.
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2014-04-29, 15:47:06
Reply #8

maru

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Most book papers use 80g/m2 or less for pages, the thickness is literally irrepresentable with physical units in CGI, because it's sub <0.1mm. Sure, carton boards (400+ g/m2) are different league.
Regardless, thick papers would be nightmare to animate in flipping fashion.

Rawalanche's advice is sound. Still, 2sided material is convenient way to have completely different material characteristic on each side, but, not any sort of priority for anyone I guess.
I can imagine a situation when such setup looks strange when viewing the book from its side. But we don't even know what exactly Juzwa is trying to achieve so let's not theorize and get back to topic. :) Also, I didn't want to sound mean.

2014-04-29, 15:52:24
Reply #9

Juzwa

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Hi,

Thanks guys for advises. However angry and prejudiced they might be.

Yes, asking questions, its just silly, i know.

CoronaFrontBackMap does the work for now

2014-04-29, 16:07:23
Reply #10

romullus

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Well I will stand with shell, as It can allow user to get some nice lookin closeups.
But I generaly realize there are better WF's.

I would choose single sided polygons even for close ups. You can simulate some thickness with rounded corner feature of CoronaMtl.
I'm not Corona Team member. Everything i say, is my personal opinion only.
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2014-10-13, 12:42:43
Reply #11

aniow

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Double sided map? :) It's called CoronaFrontBackMap. And if you instance the frontback map also to translucency slot, and give your paper material some translucency, then you will see the text on the other side of the page slightly leaking through when you look at the page against light source... like in real world ;)

Thanks!:)

2014-10-20, 15:16:36
Reply #12

robotmats

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This question has been on my mind since I first decided to try out Corona, that since it's been on my mind ever since Chaos Group introduced the 2-sided material for Vray. Why you ask? Well, becuase Vray's 2sided material isn't accurate! It does not render the way a real life flat, translucent material would do (i.e. a sheet of paper or a leaf).
I wrote a rather lengthy post about it at the Chaos Group forum: http://forums.chaosgroup.com/showthread.php?69901-The-2-sided-material-real-life-study-vs-the-rendered-version . If you don't have access to the site, I could probably repost it here, if you want.

I REALLY hope Corona can implement this, because it would enable us to render foliage (and more) in a much more realistic way.

By the way, I was not able to get a correct result using the Corona front/back-map. But who knows, maybe I'm missing something? :)

2014-10-20, 15:31:35
Reply #13

Juraj

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I wrote few of such essays too :- ) I just couldn't believe they can defend the "correctness" of that mat for vegetation by using arguments like "it's correct, it's energy conservation"; like that's all you need. They always approach everything from some strange, distanced technical view, where they can't look outside of the code and simply compare it to real-world.
What issues do you have with front back map ? I sort of like the approach, on one side you do have to put it multiple times to dif/gloss/bump slot, which is less convenient that two materials, but on other had you manage the translucency inside single shader which compensates for it.
But I didn't study it far too deeply to see shortcomings, or what's functioning differently than it should.
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2014-10-20, 18:25:12
Reply #14

robotmats

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Hehe nice to hear it. I think Vlado understood the problem eventually, but so far, no fix has been applied.

From a workflow point of view, the 2sided material works nicely. If you look at a leaf, the front and the back side will have completely different properties - the diffuse color and reflection/glossiness will be the most apparent ones. Just setting up each side as a separate material, then dropping them in a 2sided mat to add the translucency is a great idea. With front/back map, you will have to do a lot more tweaking within the material. Also, being able to simply switch between different front and back materials is easy when using the 2sided mat.

The main issue with the example in the thread over at Chaos, is that the backlit side isn't shown correctly on the other side. Also, when setting the material to the "correct" level of translucency, the material is significantly dimmed when lit from the front. Alas, this works exactly the same way in Corona. When setting a map in the Translucency slot, the material front side is dimmed, the higher you set the Fraction amount. This is not what goes on in reality. A thick piece of paper and a thin paper will look exactly the same when looked at on the lit side, but the backside of those two papers will differ a lot.

I tried to find articles explaining the way light is dispersed and reflected through leaves. (I made a thread about that on Chaos aswell haha!) I found this article, which I think is rather interesting, though I haven't set out to understand the maths of it. http://www.photobiology.info/Jacq_Ustin.html

I would imagine a perfect double sided material to work in the following way:
• Each side maintains the diffuse/bump value independently from each other
• Each side maintains the reflection/specular value independently from each other
• A translucency value directs how much of the incoming light that transmits through the object - a fill color should also be added, to simulate e.g. chlorophyll

Also, to look real:
• A fully translucent material should look the same as a non translucent one when lit from the front
• A fully translucent material should never look dimmed or darker than its back side

These points are open to debate and improvements. :)

Now, I totally see the issue with energy conservation here, and since I'm no mathematician/programmer, I can't say how to solve it. As an artist however, I can say when something doesn't look right, and so far, the double sided solutions for vray and corona are not right. ;)

(I wonder if what rendering software lacks is correct absorption and transmittance of light within objects?)