CGTalk - LightFog with mib_light

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Inky99

01-04-2011, 08:34 AM

Hi, I'm having an issue with making light fog with a spotlight, using the mib_light_spot. I haven't run into this in the past because I haven't had to make shadows with light fog.

I've used this as a guide:

http://download.autodesk.com/us/maya/2010help/index.html?url=mrfMS_Create_light_fog_using_mental_ray_for_Maya_sample_workflow.htm,topicNumber=d0e512004

And it takes you step by step through the process.

But no matter what I do, I get this ugly jagged looking stair-stepping mess:

http://farm6.static.flickr.com/5163/5322797473_d7299e1efb_b.jpg

I've tried everything I can think of to fix this, but nothing seems to work. I can make the shafts disappear, or have them turn into a big miasma of fog through the whole scene, but I can't get clean shafts with decent shadows, not without these weird artifacts.

Any help would be greatly appreciated!

Maya 2009 with Mental Ray.

noouch

01-04-2011, 09:20 AM

Have you played around with the depth jitter and volume samples parameters?

Inky99

01-04-2011, 03:58 PM

Yeah, tried both of those things. Like I said, I tried everything that it seems can be tried, in the mib_spotlight attributes, the maya spotlight attributes, the cone attributes, the lightfog attributes, and the depth map shadow attributes! I also tried to do raytrace shadows, but I get the same result.

I feel like I must be missing something somewhere.

I also tried to ramp up the render settings to "production". Didn't have any affect.

I can either make the fog turn into one big fog thing with no shadows, or I can make the fog go away completely, or I can make the shafts, as you see in the photo, get less opaque, but I can't clear up those jaggedy-looking things.

Inky99

01-07-2011, 05:58 AM

This is driving me further nuts.

I finally figured out how to get an acceptable shadowed beam of fog.

But now? I can't get more than ONE in a scene.

I make a light, get a decent shaft of fog out of it, that goes through a window and makes a beautiful shadowed pattern from the window ...

Then I dupe it ...

And the 2nd light will not have any fog. I mess around with the settings, then suddenly the 2nd light has fog, but the first one will not.

Doesn't matter how I dupe it. If I instance it, or just straight dupe.

Even if I create a 2nd light with Lightfog, the same way, only one will show fog, the others will not.

They all connect to the same Shading Engine. This may be part of the problem? I don't know.

Driving me batty ....

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