PDA

View Full Version : parti_Volume with light does not give me a matte

ragboy666
08-09-2007, 03:08 PM
If anyone can shed any.. light ... on this problem I would be greatful...

Basically I have a (maya)mental ray parti volume shader attached to a cube and a spot light, so this casts rays through the volume and I can see these in the render.

My problem is that there is no alpha under the rays. If I set matte opacity on the cube shader up to 1 then it is just a solid matte. I want to be able to overlay the rays over a background.

I have tried environment fog in MSoft, and light fog, but they dont look that great. This MR shader looks brilliant, but no matte.... arrgh

Thanks for any help.

Edd
phix314
08-11-2007, 04:40 PM
That's a tough one... google comes back with all that stuff too. I'm not near maya ATM... there's no alpha checkbox or somethin? I'm sure you've looked, but I would guess that it's nothing too ridiculous.
ragboy666
08-12-2007, 07:35 PM
Cheers

Yeah its really tricky....
You give the bounding box a shader, then asign a parti volume to the volume shader attribute of its shading group. The box shader has options for matte opacity but you can only set these to a gain level and te matte comes from the box, so you get a total spread in the matte accross the render rather than just from the light beams.

Unless you could plug in something from the light.... I dont know how to do it though...


Thanks for trying.
Ashford
08-13-2007, 04:38 AM
Hi Ragboy666,

I'll take a punt and suggest "Pass Custom Alpha Channel" needs to be turned on. It can be found in RenderGlobals|MentalRay|CustomEntities rollout (Maya 6.5).

Good luck!

Matt
ragboy666
08-14-2007, 09:35 AM
Thanks for that idea matt, but it still didnt seem to work. Not sure how to get round this one. I'm sure it must be possible....
phix314
08-15-2007, 10:42 AM
Ooh quick though, what about the primary visibility of the box? There's a few options in the attribute editor, and, again, at work so Maya is not around...
ragboy666
08-15-2007, 05:28 PM
I did try a few days ago that but get no alpha at all then. There must be a way I am not thinking of. Maybe I should ask mental images.... anyway cheers again.

Edd
phix314
08-15-2007, 06:10 PM
Now this is buggin me ;)

Maybe you need to set up a seperate pass, and combine the alpha it does give you with the rendered out greyness, then combine.

Comprende?
ragboy666
08-16-2007, 12:03 AM
I did find a bit of a fudgy solution in taking a desaturated copy of the colour channel, adding that to a copy of the alpha channel and putting it back in the alpha. It seems to work mostly, but I got so many renders I was trying to avoid it coz the deadline is looming. Anyway I wil try and post the result when I got it done. Its getting there. Shame you always have to run out of time on these projects....

Cheers again

Edd
phix314
08-16-2007, 08:45 PM
If it works.... then I guess it works.

The other day I tried slapping black surface shader onto the sphere I was using as a test and rendered it out, and the RGB seemed to work okay... that way there's no bias with the desaturated version (weight between R, G, and B values).
CGTalk Moderation
08-16-2007, 08:45 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.