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johnnynightlife
03-19-2004, 04:34 PM
i looked in the help files, and there isnt much in terms of examples, and i also did a search through this site, but didnt find much in here either. what i am trying to do is get two of my lights that are shining through two windows to have volumetric rays shining in. would this be volumetric lights or parti volume node? would anyone know of any tutorials for mental ray on these?

Profane
03-23-2004, 05:23 PM
you mean something like a fog effect like in this picture?

http://www.cgnetworks.com/galleryimages/4029/Ancient_Hall_medium.jpg

well actually i'm looking for a help too...I really dunno How to achieve this effect with mental ray....

johnnynightlife
03-23-2004, 10:46 PM
yes, thats the look im going for, there HAS to be a tutorial out here somewhere, ive used the search engine on this site, and other 3d sites, maybe im not looking hard enough?

johnnynightlife
03-23-2004, 10:53 PM
found a link, you have to search under the exact name of "parti_volume":)

johnnynightlife
03-24-2004, 02:24 AM
heres the link. this tutorial is for maya 4.5, and i have maya 5. i have followed this tutorial three times word for word, but i cant seem to get any results when i render, all's i get is a greyes out screen:hmm:http://www.motiondesign.biz/sss_3.html

Profane
03-24-2004, 12:19 PM
i'm gonna try it and then i'll say what i discovered from that.

Profane
03-24-2004, 01:14 PM
it doesn't work for me!...I think it would be more helpfull if other users would help us.

alivegy
03-24-2004, 03:11 PM
I set up a very simple scene using a little ray-marching hoping to get a volumetric effect. I believe it was a sphere in a box with a spot light. It never rendered, I let it go for about 45 minutes and the render stayed at 0% the whole time. Might be a bug or I might just not be patient enough.

I have a 2.6 p4 with 1 gig or ram, so it's usually fairly quick.

I hope to experiment with it some more later but at the moment i dont have time.

johnnynightlife
03-24-2004, 03:32 PM
(I set up a very simple scene using a little ray-marching hoping to get a volumetric effect. I believe it was a sphere in a box with a spot light. It never rendered, I let it go for about 45 minutes and the render stayed at 0% the whole time. Might be a bug or I might just not be patient enough.

I have a 2.6 p4 with 1 gig or ram, so it's usually fairly quick.

I hope to experiment with it some more later but at the moment i dont have time)
Are you running maya 4.5 or 5? i guess that tutorial was written for 4.5. I could get it to render, but it rendered gray, totally blank gray


http://www.cgtalk.com/showthread.php?s=&threadid=53900

:blush:

i also just found this thread, i guess a LOT of people are having trouble with either this tutorial, or with parti-volume, and volumertic lights. I didnt mean to start a thread that already existed, sorry everyone

Digidim
03-24-2004, 09:17 PM
Itīs rather simple:

Build a big box (surrounding your whole scene).
Give the box a new Material.
Go to MR Shader Tab for the new Material and attach a Volume Shader...a PartiVolume Shader.

For PartiVolume Shader use the following settings:

Color: How do you like it?
Extinction Coefficient: 0.001
Minimum Step Length: 0.2
Maximum Step Length: 0.4

Leave the other values at their defaults.

Now you have a something like a "room" with a bunch of "dust particles" inside of it...and any light (MR Physical Light!) inside of it can be "visible".

Create a Spot Light. Place it inside the "room". Under Export /Light Shader attach a Physical Light Shader. Give it a very huge Color Value (800000 for example).

Render the scene.

Sample Scene file attached...rename *.zip to *.rar.

Digidim
03-24-2004, 09:22 PM
Sample file pic attached:

alivegy
03-24-2004, 09:53 PM
looks good, if i remember correctly I wasn't using a physical light. This was 5.0.1. But again I really just messed with it for a few minutes.

nendo
03-25-2004, 07:45 AM
many thanks Digidim !
:)

devdoka
03-25-2004, 07:52 PM
Hey all,
Since we are on this topic
I have a few questions to ask.
In maya render,when you do light fog`s you have complete control
of how your fog looks like.
What I dont get here is how to control such attributes in
parti_volume inside MRFM?
For example,
-how can i set the fog shadow intensity and fog shadow samples?
can I do that, or do i have to trust sampling quality only in render globals?

-how can I control the fog intensity seperately from the light intensity, and the fog spreadness?

I tried the parti_volume for fog stuff but i`ve found that it is way
too slow and complicated, comparing to maya`s default one.
What confuses me most is that the maya doc`s for parti volume shader
has the exact words from the rendering for mental ray book,
which doesnt cover this subject as mush(my opinion,though i havent completely read it)
This "physical" way mental ray uses to render,
it confuses me sometimes.
Anyway,If you guys know whats going on with this shader or
know how to explain it a bit in a "maya way",
please do so.

Thanks you,

-Dennis

trthing
03-25-2004, 09:49 PM
the spotLightShapen.message should also be connected to the parti_volumen.lights[n]?

Digidim
03-26-2004, 10:05 AM
Originally posted by devdoka
....how can i set the fog shadow intensity and fog shadow samples?

Fog quality is driven by Minimum Step Length/Maximum Step Length...

...how can I control the fog intensity seperately from the light intensity, and the fog spreadness?

A lower Extinction Coefficient means more fog...you could also give the partiVolume Shader a higher Color Value to control the amount of fog...

devdoka
03-26-2004, 11:48 AM
Hi Digidim (and all others of course) again,

you said :

*Fog quality is driven by Minimum Step Length/Maximum Step Length...

but this is a general fog quality attribute,right ?
It controls both fog and fog shadow quality at the same time.
I`m interesting only in fog shadow quality.

you said :

*A lower Extinction Coefficient means more fog...you could also give the partiVolume Shader a higher Color Value to control the amount of fog...

Ok, I understand Extinction Coefficient, but even if i use it with
the color value attribute like you said,
it doesn`t give me that spreadness,
the fall off you sometimes see in the sides of the (fog) cone,
not at the end of it.

I appologise, I dont know how to explain it in a better way :(
These are the attributes i`m looking for,
unless i`m missing something obvious.

All the Best,

-Dennis

Digidim
03-26-2004, 04:46 PM
Originally posted by devdoka
...it doesn`t give me that spreadness,
the fall off you sometimes see in the sides of the (fog) cone,
not at the end of it.


Try to play with the Treshold Value you find in the Attributes for the MRPhysicalLight. This one smoothes out the "end" of the Light Cone...hope this is what you were asking for...

Chris Bacon
03-18-2005, 01:29 AM
How o you attach the Volume Shader to the cube material?????

and where do you atatch the phisical light to the spot light I cant see a export tab????

Chris Bacon
03-18-2005, 01:32 AM
Im using maya 6.0

Chris Bacon
03-18-2005, 02:05 AM
Ah Ive figgured out how to get the light working but how do you stop the light geting through surfaces and polygons. they make shdows but it doesnt stop the light it more filters it...

J-Wicz
03-18-2005, 03:32 PM
How o you attach the Volume Shader to the cube material?????

and where do you atatch the phisical light to the spot light I cant see a export tab????

MR shader are not attached to the Maya materials themself but to the Shading Group (SG) of the material.
click the outgoing connection button in the attribute editor of a Maya material to get to Shader Group attributes and there you will find a mentalray tab. Once you have done this you can use the hypershade to access them more conveniently.

btw: there is a more contemporary thread about volume effekts here
http://www.cgtalk.com/showthread.php?t=208046&highlight=volume
and this old one is also good
http://www.cgtalk.com/showthread.php?t=156886&highlight=volume

and you can search the forum there are some others about MR volume and light fog

when you have problems with light linking search for "light connection message", should help.

cheers
Philipp

Chris Bacon
03-18-2005, 06:38 PM
Ive followed the tutorials provided and so far this is what I have.....



The proble is that the light seems to just pass through the polygon wall...so I dont get that light through window effect...Any advice

Thanks.....

Ash-Man
03-20-2005, 01:26 PM
Try to play with the Treshold Value you find in the Attributes for the MRPhysicalLight. This one smoothes out the "end" of the Light Cone...hope this is what you were asking for...

First of all I like to thank Digidim for sharing this with us
as for the the Treshold Att
it control how far the light go
attached 2 images
threshold = 1
threshold = 0.5

so i guess the question still stand
how to control the smothness of that edge

Ash-Man
03-20-2005, 01:28 PM
sorry forgot the images

floze
03-20-2005, 02:43 PM
First of all I like to thank Digidim for sharing this with us
as for the the Treshold Att
it control how far the light go
attached 2 images
threshold = 1
threshold = 0.5

so i guess the question still stand
how to control the smothness of that edge
The threshold is for shadow ray optimization:
threshold is for optimization: if the illumination is less than threshold, the illumination can be discarded and no shadow rays need to be cast.
To decide how far the light should travel you could adjust the exponent of your lightsource. Another thing is the 'cone' attribute (if spotlights are being used):
cone is the cosine of the opening angle of the inner solid cone, if the shader is attached to a spot light source

ronige
05-10-2005, 02:03 PM
Maybe my MR is broken.I kan,t render the cube with a reversed normals in MR.When I render it in Maya Software everithing is just fine.If someone knows what is the problem please tell me http://us.f2.yahoofs.com/users/41de4fa0z67c97cd5/3d0f/__sr_/128b.jpg?ph.GMgCBzQiC4KAk

anthonymcgrath
08-15-2005, 02:07 PM
setting up fog and lights seems quite straightforward in mr (note to self - dont forget to connect .message to fog in connection editor!).
Is it possible tho to use a gobo in the light colour to shape the light and also decay regions to start the light at a different point along the Y value?

IlCattivo
08-24-2005, 06:14 PM
I have tried the scene that Digidim (thanks a lot) made and it works fine. But when I scale it up like 10 times it also get 10 times slover. Anyone have a sulotion or answer to this?

floze
08-24-2005, 07:05 PM
I have tried the scene that Digidim (thanks a lot) made and it works fine. But when I scale it up like 10 times it also get 10 times slover. Anyone have a sulotion or answer to this?
Readjust the min_step_len and max_step_len attributes of your parti_volume shader. These values are in world scale units, so if you scale up your scene, you virtually (and probably unnecessarily) 'lower' the step length of the ray marcher - resulting in a finer result, with higher rendering times. To get the same result as before, scale the min/max_step_len by the same value you scaled your scene with.

IlCattivo
08-24-2005, 08:41 PM
Saved my day, thanks man!

anthonymcgrath
08-25-2005, 07:24 AM
yeah same thing used to happen in softimage - its a very similar method - I used to up the min and max samples so it was really blocky and naff sampling - almost not there haha then lower it till I got acceptable results - works for a still image but animation usually requires a little higher sampling or you see the raymarching steps ook!

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