mental ray parti_volume problems....

[Jozvex]

Have you got Depth Map shadows turned on? Lights will shine straight through things without shadows.

Raytraced shadows don't get cast into fog.

[floze]

Raytraced shadows don't get cast into fog.
I thought that too for a while, but it's not true. Increase your shadow trace depth, up to 10 or even more.

[Louie]

k thanks, i actually using ray traced shadows, so i'll try uping the values, another thing im trying to make the sillohette of the object appear more, the basic set up is that i have a polygon shape then i turned off the visibility of the shape so all you see is the void of light that the parti-volume leaves behind, i was thinking of adding more geometry, maybe duplicate it so it will intensify the shadow, or even increase the min max step lens on the parti volume attribute, do you guys have anymore suggestion.............

thanks,

louie

[anthonymcgrath]

I still couldn't get any volume shadows into my scene using depth map or raytraced :(

floze you say increase the shadow trace depth - I did that in my render globals upping it to 10 but now I've got other shadow rays counts:

in my ctrl_geocolour node I have a shadows box - thats got a trace depth thats by default at 2

my light is a physical one

then in the node above this one (geolightshape) under its 'raytrace shadow attributes' I have light radius, shadow rays and ray depth limit.

I've swotted up on these but my whole prob now is I'm lost on whats overriding what! :shrug:

can you elaborate more on how to get the vol shadows in my parti volume or have more control on them?

[slipknot66]

I think we did this before... here is a link..

http://forums.cgsociety.org/showthread.php?t=156886&highlight=slipknot66

[floze]

can you elaborate more on how to get the vol shadows in my parti volume or have more control on them?
The magic shadow trace depth seems to be 4. You need to set it both in your light shader and in the globals. The light's settings get clamped by the global settings. Working test scene attached:

http://individual.floze.de/fileadmin/files/cgtalk/parti_volume.zip

Note: You need a) a surrounding/background object, like the box in my test scene - else the fog wont be visible, and b) you need to specify the lights in the parti_volume, which is attached to the camera's volume shader slot. The parti_volume does not seem to loop over the lights by default, it needs them properly listed.

[anthonymcgrath]

nice one cheers Floze I'll give that a shot - so basically the lights HAVE to be listed in the parti_volume 'lights' box?

I notice you mention putting the volume shader into the CAMERA's volume shader slot and not the volumeBox SG/MR/volumeShader slot? I've heard of doing this but I haven't bothered because I'm told its much much slower! is this true - have you noticed a difference?

cheers
ant

[floze]

nice one cheers Floze I'll give that a shot - so basically the lights HAVE to be listed in the parti_volume 'lights' box?

I notice you mention putting the volume shader into the CAMERA's volume shader slot and not the volumeBox SG/MR/volumeShader slot? I've heard of doing this but I haven't bothered because I'm told its much much slower! is this true - have you noticed a difference?

cheers
ant
The lights do have to be listed, yes.

Using some volume box speeds up rendering, because any ray that doesnt hit anything would become 'void'. And thats why you wont see the fog if there isnt any object behind - in fact, every object would cut out the fog where it occludes the environment - all unoccluded parts would get the environment color.

So basically, if you have a fully environment occluding scene, it would render as fast as if the parti_volume was plugged into the camera. I guess.

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