I want to mix two renderes. That is, I want to render nearly everything using wren, and then just a volumetric light using mantra. And then mix all that stuff in somewhere…

I can compose it normally since the volumetric light will be in between the objects in wren, si I need z-buf composition.

Is this what I ask possible, or am i dreaming?

Well I used wren as a rendering for one layer and then did another in mantra. I used the alpha channels with black set as the transparency. if you render that lighting against a black background with alpha set on and render to tif for a composite it should work. You might have to use something like volumetric fog to pick up the lighting or what not. I am not really sure what you are trying to do specifically. I might be looking at a solution from another angle to that you don't want. Does that help any?

Cheers,
Nate Nesler

Ummm… yeah, sorta. I was thinking of using the z channel for composition, because I have stuff that need to be rendered in wren right in front of the camera, closer to the camera than the volumetric light, and also trees behind the volumetric light.

Umm… so yeah, z-channel and alpha.

I used Gimp to convert the black background from wren to an alpha channel. I think what you are wanting to do will work fine. If you have a problem with it though you can just put it out to black background with wren and then convert the black to alpha with gimp or photoshop or whatever you like to use. I had a problem with wren when I tried to output to the alpha channel it just gave me a black background. You might run into this I don't know but thats how I got around it. This was my end result.

Cheers,
Nate Nesler

ok, problem.

It's an animation, 3750 frames of it. I'm not going to go one-by-one doing that.

Other problem, i need wren-rendered trees in front AND behind of the mantra-rendered volumetric light. The trees in front should totally block the volumetric light, so it's not a matter of alphaing the black. I need the z-channel.

I've played around with the compositor, and it seems to be working fine. I used a zcomp COP2, and so far, the tests are great. (haven't put in the volumetric yet!)

Well the 3,750 frames is not a problem in Gimp you could simply automate the process with Script Fu, Perl, or Python. The code would be just a few lines run through a loop. thats it. Like you said, though, that would not solve it for the z-channel. I can't think of how I would get around that if it did not work. hope it all works out for you. Well actually I do have one idea if you can not get the volmetric lighting to render in wren couldn't you try it in mantra as a seperate layer all by itself and then composite it in as a seperate layer. I mean why would you nessicarily have to render the volumetric lighting in wren. Why not mantra as a layer by itself?

Cheers,
Nate Nesler

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