refraction bug?

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  04 April 2002
Unhappy refraction bug?

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.
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Kris Rivel
Senior 3D Artist
Active Black
www.activeblack.com
 
  04 April 2002
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.
 
  04 April 2002
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.
__________________
Kris Rivel
Senior 3D Artist
Active Black
www.activeblack.com
 
  04 April 2002
this is maybe just the slider range that is wrong..
 
  04 April 2002
@@@@
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/sho...&sb=5&o=&fpart=


Salutations - Cheers
Bernard Lebel
 
  04 April 2002
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:

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
 
  04 April 2002
Question

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.
Attached Images
File Type: jpg bug.jpg (5.9 KB, 590 views)
 
  04 April 2002
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
 
  04 April 2002
To Atyss:

Yes, it was the problem, thanks.
 
  04 April 2002
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.
__________________
Kris Rivel
Senior 3D Artist
Active Black
www.activeblack.com
 
  04 April 2002
Workaround here

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.



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.
__________________
guy rabiller | 3d animator / td @ LaMaison
 
  04 April 2002
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
 
  04 April 2002
Hi Markus,

Of course it should works without this node.

This is simply a bug ( a forgetting ).

Hope they will fix it soon.


Guy.
__________________
guy rabiller | 3d animator / td @ LaMaison
 
  04 April 2002
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.
__________________
Kris Rivel
Senior 3D Artist
Active Black
www.activeblack.com
 
  04 April 2002
I could not agree with SMedic

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.






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
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:)

Last edited by Jonson_lee : 04 April 2002 at 11:16 AM.
 
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