Light Fog.

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Old 07 July 2004   #1
Light Fog.

Hey there, I am making preparations for my next project. Trying to clear out issues before they rise.
One of them is light fog.
Here is the test scene:


What way should I use to get nice light fog from the window to the floor where highligh is happening. If using traditional spotlight and enabling light fog, you get circular light fog cone. If I resize that cone larger than window, weird artifacts start to happen. So I understand the cone border detects where fog should happen, and if it hits mesh it disables fog behind that mesh.
Here is the reference what I like and would like to know how it was made:


Prefferably I would like to render it as separate pass and comp it together later. I am willing to learn but have no idea where to start, any tips or hints are very welcome.
Thank you
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Nerve Attenuation System Advancement > Mindcircus
 
Old 07 July 2004   #2
well... i think the best way to achieve that result, is mapping your image to the color light slot.
 
Old 07 July 2004   #3
Sry slipknot66 but you are missing my point here. Lets wait if someone else understands what I am trying to do. If noone will answer I'll try to express myself better.
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Nerve Attenuation System Advancement > Mindcircus
 
Old 07 July 2004   #4
There are many god rays plugins and scripts that can do this in most compositors.

For example, genarts sapphire:
http://www.genarts.com/
or the foundry tinder
http://www.thefoundry.co.uk/
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-deke
 
Old 07 July 2004   #5
Well I think slipknot66 is right. In the 2nd picture you posted the person mapped the stainglass texture to the colour slot of the light, turned on light fog, probably with a decay rate. Your window is square so you can adjust the barn doors if you are getting artifacts.

Last edited by Tierackk : 07 July 2004 at 09:54 PM.
 
Old 07 July 2004   #6
That second picture is from MR's feature list page.
Yes I have thought to make those volumetric rays directly in comp but as I got some time, I would like to learn something new.
OK, adding color to the spotlight and enabling light fog. Thats exactly what I've been trying to do since from the beginning. I ran into trouble and was wondering that maybe it is some kind of common mistake.

Anyway, here is the same scene what I gave as a example. But here light fog is enabled and also a fractial is connected to spotlights color. Everything is fine until the cone is smaller than my square window:


But now, once I resize the cone so that it is bigger than my square window:


Thats what's giving me problems. I guess mayas standard light fog is entirely 2D effect, or I am doing something completly wrong.
If you look again now that Mental Ray pic, its all fine there
Wonder how that pic is made.
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Nerve Attenuation System Advancement > Mindcircus
 
Old 07 July 2004   #7
i think i found a solution, check this tutorial, im trying this one too

http://www.motiondesign.biz/vol_start.html
 
Old 07 July 2004   #8
well... here is what i got until now, playing with volume photons etc... now im melting my brain trying to find a way to emmit some colors..

 
Old 07 July 2004   #9
Use a 3dFluid as fog, map the color to the light, render in mentalray with raytrace shadows. In my experience, it's faster then using parti shaders.

-z

EDIT: actually, it's even better to model the window, and map the transperancy of the window with the color. See attached example.
Attached Files
File Type: zip fog_test.zip (9.1 KB, 459 views)

Last edited by zylphyr : 07 July 2004 at 08:47 AM.
 
Old 07 July 2004   #10
You can change the Fog Color by changing the Scatter Color on ur Parti_Volume shader assigned to the Bounding Box if thats what ur trying to do!
 
Old 07 July 2004   #11
Thank guys alot
slipknot66, I also found this tutorial but for some reason I was thining that altough it seems similar, it is not very good for simple volumetric light.
Anyway, now I got something to start with, thank you guys very much again
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Nerve Attenuation System Advancement > Mindcircus
 
Old 07 July 2004   #12
Hey zylphyr, thank you again for the scene. I think it will work very good for what I need it to do. And depending on the fluid complexity it renders very fast too.

slipknot66, were you able to attach color to those volumetrics, and could you add abit grain too. Could you tell me what was the rendering time on the last pic. Or if you can make new tests, I would be interested to know.
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Nerve Attenuation System Advancement > Mindcircus
 
Old 07 July 2004   #13
Hey, I've been playing with volume fog in mental ray recently. I've managed to get the fog too be non-homogenous byt just setting the uniform value of the parti_volume to something other than 0 (the closer to 1, the more the fog billows).
As for colours, you can set the fog colour, but I haven't yet tried to add patters of colour (as if it is coming through a stained glass window).
I will try that tonite though. If I come up with anything, I'll post it here.
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Old 07 July 2004   #14
ok.. now the light is generating colors, but is passing thru the objects.. i think is something wrong with the shadows, im using raytraced shadows....



the firts image i posted i was using a mentalray spotlight, now im using a maya default light
 
Old 07 July 2004   #15
You are getting photon leaking above the window. You'll need to increase the subdivisions for your wall and or ceiling to fix that. The reason that occurs is due to the GI radius being too large and the photons consider the radius on both sides of the wall instead of being blocked because the photons consider vert information when calculating the accuracy. You can raise the GI accuracy to compensate for that but it will increase your render time of course, or what I tend to do is add more subdivisions in the problamatic areas. That tends to take less of a hit on rendering than increasing the accuracry settings.

Last edited by BillSpradlin : 07 July 2004 at 06:04 PM.
 
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