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zelda64
07-02-2011, 03:46 AM
Hi

I use Maya 2011 and Mental Ray.

I assign a mia_material_x_pass to a object and try casting transparency shadow for it and everyting
is OK .

http://up.iranblog.com/images/vbqitrqbsqhynranolnq.jpg

But when I try to cast caustic effect for object (Refractive Caustic parameter is select in mia_material) with caustic effect it's casted a opaque shadow.

http://up.iranblog.com/images/p090qocu8xjdbnwto1va.jpg

I need caustic effect + transparency shadow

What do I do.

Please Help Me.

Kakkoii
07-02-2011, 04:22 AM
Caustics are a simulation of how light bends, refractions and focuses through or off a material. The shadows aren't going to look the same because the light is being bent and focused by the object like it would in a lens, so naturally you wouldn't get this perfect shadow gradient you see in the first image. What you are seeing in the second image is more realistic, although still a bit wrong since your shadows likely aren't set to Segments.

Render Settings> Quality > Shadows > Shadow Method > Segments

zelda64
07-02-2011, 04:59 AM
Thanks Kakkoii very appreciate.

But are you can tell me what is wrong . because it is in "Segment" mode.

Kakkoii
07-02-2011, 06:09 AM
There's nothing to fix really. The object is behaving properly, it's conserving energy. Since the light going in is being focused into a smaller area, the other parts around it will be receiving less light, and thus will become darker shadowed areas.

You shouldn't be using a Spot light though, because it's casting light from an infinitely small point in space, which will give you unrealistic looking rendering. Change the spot light to an area light, or use a mental ray light surface shader on a piece of geometry to cast the light.

Plus the fact you have no other light sources in the scene makes the effect look even more unnatural.

Find a glass object in your house, preferably with color, if you have one. Bring it into a pitch black room like the bathroom with a small flash light and simulate your scene. You'll see that the light behaves in a similar way.

Examples: (Not my renders, from the net)
http://vray.info/assets/keith_caustic_subdiv2000.jpg
http://graphics.cs.kuleuven.be/renderpark/SCREENSHOTS/egg_caustic.jpg
http://www.kxcad.net/autodesk/maya/Maya_Documentation/ArchGuide/images/bottle-caustic.jpg
http://www.nvidia.co.in/docs/CP/13159/caustic.jpg

And a photo:
http://www.mpi-inf.mpg.de/departments/irg3/ws0304/lcn/projects/Michael/waterglass_caustic.jpg

zelda64
07-03-2011, 06:44 AM
Thank you for your advice Kakkoii . its perfect very appreciate.

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