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krisr
04-14-2002, 11:32 AM
ok, I know I've seen this posted a few times but I can't seem to remember the solution. Why is the refraction settings in XSI not work properly? For example, a refraction setting of 1.4 in XSI is not the same as a refraction setting of 1.4 in Si3d.....it seems to be incorrect.

dmonk
04-14-2002, 08:19 PM
In the reference books and the online library in the shaders section there a chart that gives you settings for what refractive index is right for what material. there pretty good to use for a comparison to get what you want. If I find the list I'lll post a reply.

krisr
04-14-2002, 09:41 PM
yo Tony, thanks for the tip but what the online reference stuff says and what the book says is right I'm sure but it doesn't produce the same results. Refraction for glass for example should be something like 1.4 to 1.6. Its the same for Si3D and for XSI. Create the same exact scene and apply the same settings in Si3d and XSI and you'll see what I mean........very strange. I saw somebody on the Soft user group post a link showing this example but I can't seem to find it.

mr-doOo
04-14-2002, 09:48 PM
this is maybe just the slider range that is wrong..

Atyss
04-14-2002, 11:04 PM
@@@@
I saw somebody on the Soft user group post a link showing this example but I can't seem to find it.
@@@@

Bonjour Kris,

The link your looking for is this:http://www.highend3d.com/boards/showflat.php?Cat=&Board=xsirender&Number=97795&page=1&view=collapsed&sb=5&o=&fpart=


Salutations - Cheers
Bernard Lebel

Markus
04-14-2002, 11:06 PM
Yes, there is definitely a bug concerning refraction.
Softimage has confirmed this bug.
You can easily compare it inside XSI when you load an SI 3D shader. You can load it by Get>Material>more...>browse for soft3d and choose Peekaboo or Velvet. These shaders do refraction right.
Simple example:
http://jechtech.de/glass1.jpg
You can see on the left side that with the XSI shader the rays are only refracted by the first surface of the object pointing towards the camera. The rays go straight trough the surfaces lying behind.

Markus

cmortier
04-15-2002, 12:15 AM
I don't know if this is the same bug, but it seem that when I try to render a simple torus with transparency (index 1), I get the backfaces black. Here is a picture.

Atyss
04-15-2002, 02:06 AM
Go into Render module > Render > Render > Options, then in Optimization tab. Under Raytracing Depth, put 5 as Refraction and 7 as Maximum Ray Depth. It should do the trick.


Hope this helps
Salutations - Cheers
Bernard Lebel

cmortier
04-15-2002, 02:56 AM
To Atyss:

Yes, it was the problem, thanks.

krisr
04-15-2002, 07:49 PM
Ahhhhh....thanks Markus....I knew I saw this somewhere. I sure wish somebody at Soft could give us answers to this....this is a HUGE bug. I'm sure not everyone out there needs to model a wine glass but am I supposed to just continue my work knowing that anything I make resembling glass is false!!!??? C'mon.

SMedic
04-16-2002, 12:56 AM
Hi,

this has to do with a front/back switching issue with XSI shaders.

Just add a front/back switch node to get proper refraction.

http://grabiller.3dvf.net/site/download/XSI_Refraction.jpg

The second node connected to the back input should have a refraction index of 1.0 ( or the one of the outside medium ).

Hope this helps.

Guy.

Markus
04-16-2002, 01:11 AM
One must know that!
Thanks a lot!:)
I didnīt find this in any manual, tutorial or forum. Even people from softimage couldnīt help me and said this must be bug.
But shouldnīt it work correctly by default without this node?
It seems to be a bit complicated for such an easy thing.

Markus

SMedic
04-16-2002, 01:49 AM
Hi Markus,

Of course it should works without this node.

This is simply a bug ( a forgetting ).

Hope they will fix it soon.


Guy.

krisr
04-16-2002, 02:29 AM
wow, thanks Guy, glad to know there's a workaround.....that's frickin ridiculous if you ask me. I really hope they address this bug ASAP.

Jonson_lee
04-16-2002, 12:13 PM
I could not agree with SMedic
The front/back switch node does not consider the camera POS and the model`s shap, if you look through the cup from top, you will find the refraction is not proper.


http://www.chinadv.com/bbs/photo/200241614924228.jpg

http://www.chinadv.com/bbs/photo/2002416141013228.jpg

Front/back switch node just like dual shap way (I copy the cup,invert the normals, set IOR=1, transparency=1,simulate the air refraction face,and SET render option >optimization>face mode>front1), that`s not the perfect one !

2 years ago ,I found this bug , I sent a email to softimage, but they did not reply ,I hope they fix it soon

waterblue_xsi@163.com
waterblue_2002@yahoo.com

SMedic
04-16-2002, 01:51 PM
Obviously there is something wrong with your setup and/or rendertree.

Here, both are strickly identical in terms of refraction.

http://grabiller.3dvf.net/site/download/fromtop.jpg

Front/back switch node just like dual shap way (I copy the cup,invert the normals, set IOR=1, transparency=1,simulate the air refraction face,and SET render option >optimization>face mode>front1), that`s not the perfect one !

That *is* the perfect way, whatever you use a duplicate/inversed object or a front/back node.

Internaly, Mental Ray shaders work this way.

And to be more precise, the back refraction should be set on 1/ior of the front refraction.

Hope this helps.


Guy.

Jonson_lee
04-16-2002, 05:04 PM
@Obviously there is something wrong with your setup and/or rendertree.

I can`t believe that , I think there`s no wrong with my rendertree&setup

@Internaly, Mental Ray shaders work this way.
really ? could u prompt me how does MR work in this way?

SMedic
04-16-2002, 07:49 PM
I can`t believe that , I think there`s no wrong with my rendertree&setup

Well, how do you explain that it is working here, and not with your setup ?

@Internaly, Mental Ray shaders work this way. really ? could u prompt me how does MR work in this way?

Internally MR just use a front/back switch. The front/back switch node you have in the rendertree is a Mental Image Shader that 'exposes' this.

Take a look at the Mental Ray documentation and the sources of the Mental Image shaders ( on the Mental Images ftp ).


Guy

Jonson_lee
04-16-2002, 10:31 PM
HEY SMedic
The attach file is my scene , I could not find out what`s wrong with my rendertree/setup. Could you give me your scene ?

http://www.chinadv.com/bbs/photo/20024170222228.jpg

cmortier
04-16-2002, 11:08 PM
Ok Jonson_lee ,

I download your scene .

Try to invert the refraction of your 2 phong shaders put 1.5 instead of 1 and 1 instead of 1.5 and it will work fine.
Don't know why.
You can simply switch front and back, it will do the same.

Chris

SMedic
04-16-2002, 11:49 PM
Hey Jonson_lee :-)

Just invert the normals of your objects.

Both are inverted, but in the case of Peekaboo, the shader automaticaly detect the front/back so it is still correct.

In case of the other object, you 'force' the front/back switching mechanism with normals inverted, so obviously, it gives wrong refraction result.

Always check your normals :-)


Guy.

Jonson_lee
04-17-2002, 11:23 AM
hey all
thx a lot!

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