MR ambient occlusion problem

# 1 02-02-2012 , 07:26 PM

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Join Date: Oct 2011

Posts: 139

I set up an ambient occlusion for mental ray render:

I picked mia_material_x_passes. Added mib_amb_occlusion nod to it on default settings, and finally applied the material to my objects. Now with the lights on everything works, but once I turn them off (and I have to, since I don't want shadows cast in my AO pass) everything is black.

I'm not supposed to need any light source for AO to work (at least I don't if I do it as render layer), but for a specific reason I have to have this AO rendered by MR. What am I doing wrong?

P.S.: I'm also not sure I render it correctly. Since I've already rendered the regular pass, I just render this as is... I don't uses passes in MR. I tested AO pass, just to see if it works but it doesn't.

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# 2 02-02-2012 , 07:34 PM

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Join Date: Feb 2004

Location: Chicago

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just as an easy fix you can turn off cast shadows in your lights.

but here it's free https://simplymaya.com/autodesk-maya-...rs/?tut_id=180

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Last edited by jsprogg; 02-02-2012 at 07:42 PM.

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# 3 02-02-2012 , 07:50 PM

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Thanks JSprogg for sending the link

J

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# 4 02-02-2012 , 07:53 PM

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What I do:

1) Create "SurfaceShader"
2) Add a "Mib_amb_occlusion"
3) Place the "Mib_amb_occlusion" in to the out color of the "SurfaceShader"
4) Change the settings for your needs.
5) Apply the shadder to your items
6) Render using MR.

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# 5 02-02-2012 , 07:59 PM

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Thanks for the reply. I can't use the method from the tutorial because my scene includes tree (so I have to apply a special AO material to it with alpha channel to have the leaves appear correctly). I have been trying to do it some time ago, but after spending too much time on it I gave up and just recently went back to it.. you can see the original post here:

https://simplymaya.com/forum/showthread.php?t=36842

I am now able to create the materials (two of them: specific one for the leaves, and regular for everything else). I can see the final image just fine, but I don't want my scene lights effect the AO in any way, so I turn them all off (so that my work area is all black), this should not affect the render, but it does. The render is all black.

I can turn of casting shadows on all my lights, but wouldn't the light still affect the AO? I want the same amount of light everywhere in the scene..

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# 6 03-02-2012 , 03:27 AM

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I hate to do this.. I was determined to figure this out by myself, but am now running out of time and after spending the whole day and failing time after time.. I've got to ask you for help directly. If anybody here wouldn't mind taking a few minutes to look at my file and setting the material to work, please PM me and I will email you the file. Your help would mean a lot..

Here is the problem:
I have a scene with a house and a tree in it. The tree has leaves with alpha channels (paint effect tree converted to polygons). I want to render an AO pass of the scene. I set up two surface shaders, one for the leaves and one for the rest of the scene. The shader for the leaves have the texture plugged in and out_transparency on both sides, but I'm still getting those weird outlines around the leaves. I have also tried the method that Genny suggested in the previous thread using mia_material_x but failed at that too (the render takes a VERY long time and everything is black).

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# 7 03-02-2012 , 04:22 AM

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I dont know if you can get it...free.....find Crazybump...I use it....there you import your colour render...and crazybump will do the rest...see how you go.

cheers bullet

bullet1968

"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes

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