View Full Version : God Rays in Maya?

12 December 2011, 10:10 AM
Im currently working on an animation project in school. The scenery is an old temple ruin:
(This picture ha some old textures, mssing speculars, bad shadows etc, but just to show you the setting).

Apart from the torch-thingy the character will carry I want the only light to come from holes in the ceiling. To make this look nice I would like to use "God rays". So that the light coming from the ceiling is visible, maybe with some dust moving in it etc.

Now to the problem: How do I make God Rays?

What I have tried:
- Make a box covering the whole scene and put a transmat and particle volume on it. Never got to see the result because it took ages rendering it. Maybe some settings needed to change? Rendering time cant be too long, because I have limited time (Some minutes/frame).

- Spotlight with "light fog". Looked "ok" I guess, but if I covered the spotlight "cone" partly (to make it cast light of the same shape as the hole in the roof) then the fog dissapeared.

Please help me =/. Are there any nice God Rays-plugin for Maya? Maybe I can use alpha planes or something? Dont know what to do..

Sorry for my bad english, not my main language.

12 December 2011, 06:17 PM
I think the terminology involved may be keeping you from receiving many answers. "Volumetric lighting" is often referred to as "god rays" by the Vue crowd, as it's got fewer syllables to help them keep it simple. (grins)

To achieve volumetric lighting in mental ray, you have three good options.

1. parti_volume (participating media volume) which you've tried. How did your preview renders look? You can tune the parti_volume to be relatively quick, it really just depends on how clean you need it to look. But if you need accuracy, that's your best choice. The math involved is hefty compared to any other kind of lighting, and thus, the rendertimes are gonna hurt.

2. Light fog from a spotlight. This one won't produce the light streams relative to occluding objects (a person passing through) accurately, however you can map a texture to the light to simulate this effect if necessary.

3. A simple textured cone. Likely the cheapest/quickest way but also not going to give you any physical accuracy.

I tend to use parti_volume most often, and just tune it so I get a decent balance of quality/speed.

12 December 2011, 10:41 AM
Depending on animation requirements, maybe you could do them entirely in After Effects or a similar program?

Your English seems better than a lot of English people's English...

12 December 2011, 08:54 AM
Hey, thanks for the responses :).

I ran out of time and solved the problem a week ago. I used several planes (12 or something I think, dont have the file on this computer) which I gave a .png texture with a thin low opacity light ray painted on it. I then crossed 2 of these planes so that it made a cross. I then dublicated this cross and moved them around and created a starlike shape with them, some I rotated 45degrees. I moved up the outer crosses in Y to make a pointy shape and then combined - fixed pivot and made them rotate.
Looks something like this, (this isnt the latest version).

Should be watchable any minute.

12 December 2011, 08:31 PM
Weird, Im pretty sure I wrote a reply here. Maybe my connection broke :S.

Anyway, thanks for the answers :). I did solve the problem a week ago and I think it turned out ok. I used several planes with a low opacity light ray painted on it which I then grouped and animated with a slow rotation in Y. Looks something like this:
(It has been tweeked a bit since then, but you get the idea).

Im still intrested in how to tweak parti volume to not take so long in render though. Any link to a nice guide to that or something would be appriciated! :)

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12 December 2011, 08:31 PM
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