C6 Pro, help needed: rendering transparent planes inside a fog primitive

Mustakettu85 · April 2013

Hello everyone,

Sorry for intruding into what looks to be a closely knit community, but I've run into a problem I can't resolve by myself... There is a chance it cannot be resolved at all, but there is no way of knowing it without asking first. So please bear with me. And help would be much appreciated.

I use C6 Pro which is old but I cannot afford an upgrade, unfortunately. It's just a hobby for me.

I'm working on this scene where I needed a lot of different flames. I made a shader using the "Fire" natural function in Transparency and Glow channels (the rest are set to "none"), as described in the manual. I just can't get the Fire primitive to look the way I want, and I'm perfectly happy with the shader.

I applied the shader to "splats" (billboard planes). The lights are shape lights set to rings. It all looks awesome, but I felt the scene needed something prettier like a glow or a fog effect (which are not really nice to introduce in postwork when you have no drawing tablet; simple "glow" filters in image editors make every lighter-coloured surface glow, and it's not always desirable).

I tried using the 3D Aura effect, but it didn't work well with the transparent planes (it seems to think the whole plane glows, while only the non-transparent part does).

I added a fog primitive, which looks better, but you can still see the outlines of the plane billboards, even though the planes do not cast or receive shadows.

I've tried everything I could think of - playing with the fog quality parameter, getting rid of any GI including AO, checking all the "light through transparency" boxes, turning ambient off, using inverted Fire shader in the Alpha channel, excluding planes and fog from interacting with lights... even changed the diameters of the ring lights thinking it's their fault, but nope, it's purely the effect the planes produce. Nothing changes.

Is this possible to remedy without postwork, or is this a known bug/feature, or something?

Thanks in advance.

wetcircuit · April 2013

Hi! Certainly no intrusion! Everyone is welcome! :coolgrin:

I remember having this issue with the flame texture on a splat... I do not remember if I ever fixed it...

Unfortunately I *believe* it may be an unsolvable issue in C6 -- although please see if an update is offered I think the final version was 6.2 and there were some transparency issues that were fixed....

Unless someone has a better idea, I would suggest doing 2 renders, one pass without the flames (hide the splats), and the other pass no lights just glowing flames

Headwax · April 2013

splats act strangely even if the shadows are unchecked

could be the edge of the apha map isn't completely black
if you just put a 100 percent alpha on the billboards what happens?

1) one thing you could try is just add the texture to an ordinary flat mesh and use the point at modifier to get it to point at the camera

that said Carrara acts odd with some primitives and alpha maps and lights as far as I can recall

2) does it act the same with eg spot lights ?

3) the fog always looks weird to me
I'd try dropping in a cloud to replace the fog and see what happens
might be just the same

4) Holly's suggestion sounds good
post work is easy sometimes

Mustakettu85 · April 2013

Thanks a lot for replying and welcoming me, folks! =)

I'm running version 6.2.1.18, and it looks like the fog primitive is particularly capricious... The upside-down flame is a "normal" plane pointing at the camera, and you can see it has the same effect, same as when alpha is turned down - you can still notice the outline of the plane. It gets particularly noticeable with bulb lights instead of shape lights...

A volumetric cloud makes it less noticeable, but it introduces these bright patches above lights (any lights, bulbs or shapes) that I'm not sure I want.

So I guess Holly's separate passes solution is probably the best, but I'll try experimenting with the volumetric cloud further to see what could happen =)

Thanks again!

PS This forum software really hates me =(( It keeps taking me to "my account" instead of posting the reply.

evilproducer · April 2013

Even in version 7, alphas and volumetric clouds don't play nice. I would assume that the fog primitive would have the same issue. Post work is probably the quickest possibility.

One question, did you try applying the map to the transparency channel only to see if the effect occurred with the fog or volumetric effects?

BTW, you could render the fog or clouds a separate pass. No need for a tablet. See my composite test animation:
http://www.youtube.com/watch?v=79fyKOSUTsg&feature=share&list=UU6wB1FKPN4DWpuoVsQY2o8Q

Mustakettu85 · April 2013

evilproducer said:
Even in version 7, alphas and volumetric clouds don't play nice. I would assume that the fog primitive would have the same issue. Post work is probably the quickest possibility.

One question, did you try applying the map to the transparency channel only to see if the effect occurred with the fog or volumetric effects?

BTW, you could render the fog or clouds a separate pass. No need for a tablet. See my composite test animation:
http://www.youtube.com/watch?v=79fyKOSUTsg&feature=share&list=UU6wB1FKPN4DWpuoVsQY2o8Q

Transparencies and alphas, both make the fog primitive very unhappy. A volumetric cloud is more tolerant, but it can "see" the rest of the plane, too, specifically with simpler lights like bulbs (even if you ADD them to the scene lit by shape lights and then turn the bulbs OFF!! See attached render; now this is beyond me LOL)

And that's a nifty animation, very StarWars'y type of asteroid field =)

Headwax · April 2013

hello this is from playing in c8
I can't see that c8 would have improved since c6 in this regard so I am guessing it should work for you

dump the splats
insert a polygon sphere instead
apply the fire textures in the shader room in the alpha channel and the colour channel and glow channel
in the glow channel add an operator mixer and use the second source as the colour black and the mixer as a slider 0 to 100
remove all highlights
go into the model room and make sure your uvees are lining up as you like
in the assembly room use the point at modifier
add a cloud
you will still see the edges of the mesh
export the mesh as an o bject
also export the textures as high resolution as possible
in photoshop open up the fire texture
add a layer
fill it with proper black
erase carefully with a soft edged brush
so that you leave proper black at the edges of the map
bring this modified texture into carrara and apply to glow, alpha , colour and
with a normal distance light with no soft shadows etc
and your problems should be solved

notes

it appears the fire texture in carrara doesnt' have propetr black
if you use a splat I can't see how you can control where the texture sits on the splat
you could probably use a planar polygon and get good results
remove shadows from the mesh you have as the fire

Mustakettu85 · April 2013

Thanks HeadWax! Gotta try this, too.

As for how to control the way the texture sits on the splat - it sits wherever it wants, I just scale, rotate and move the splat =) It's a bit crazy, agreed. A "normal" planar surface needs the same coordinate tweaking as well...

Looks like no Carrara beta testers ever were rendering flames in fog XD

wetcircuit · April 2013

Mustakettu85 said:

Looks like no Carrara beta testers ever were rendering flames in fog XD

I think it's more than "just a bug". It has to do with the order in which volumetrics get rendered. There is a "loop" in which items are rendered in a specific order based on their shader, position, transparency, lighting, etc... Items which have no geometry like volumetric fog, light rays, hair, are also rendered in a particular order, which leads to problems with them unable to "play nice" with each other. I'm sure I'm oversimplifying it, but it requires the "loop" to be run twice to find elements that might conflict and that might more than double the rendertime, or require entire rewrites of legacy features....

For what it's worth both C7 and C8 have seen a lot of updates with transparency and also the issue of multiple volumetric objects getting brighter because they get composited into the image as an additive layer... I think there are still problems with hair and fog together, but there have been improvements. C8Pro has multi-pass rendering which makes separating out these layers in a render much easier too.

I don't think I said before but those skull candles are cute and I love the colors in your render...

Mustakettu85 · April 2013

holly wetcircuit said:
I'm sure I'm oversimplifying it, but it requires the "loop" to be run twice to find elements that might conflict and that might more than double the rendertime, or require entire rewrites of legacy features....
Yes, that sounds quite likely. Are there any original developers left? Gotta be a nightmare trying to refine work done by a different team...

holly wetcircuit said:
C8Pro has multi-pass rendering which makes separating out these layers in a render much easier too.

That's cool! I'm definitely planning to upgrade... one day.

I don't think I said before but those skull candles are cute and I love the colors in your render...

Aww thanks! It's a fanart project actually, trying to recreate a location from an old game, Hexen. I did a similar one for its predecessor, Heretic: http://mustakettu85.deviantart.com/art/Heretic-Entering-the-Cathedral-299231610

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C6 Pro, help needed: rendering transparent planes inside a fog primitive

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