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View Full Version : Rendering: Fog + Opacity-mapped polys = woe

Toxic Frog
06-07-2004, 09:35 PM
Here's a situation I haven't found a solution to, and I'm hoping someone here can help me:

I have opacity-mapped tree limbs in a low-poly scene. I want to add fog (Max's default fog, set with near/far values on the camera).

The problem is that the fog is rendering the polys where they should be invisible. You can see the edges of the polys when the fog affects them, when it should only render the visible parts of the polys as defined by the opacity map.

I checked 'exponential' in the fog settings, but that didn't help. I double-checked the opacity maps (in this case the alpha channel of the image) and it is perfectly black (0,0,0).

Any help will be VERY much appreciated.
Thanks
Cullen
06-07-2004, 10:07 PM
Same thing happened to us a month ago. We just rendered one version with fog. Another with "alphaed" elements (everything else shadow mat material) without fog. And comped the second layer over the first.

Pain in the ass? Yes.
But if you have to do it than you have to do it.

I would also like to know the correct solution though... if anyone has one.
jbrophy
06-07-2004, 10:11 PM
Odd

Exponential has always fixed this for me
gjpetch
06-08-2004, 01:48 AM
It does suck. I don't know of any really good solution, just recently I used falloff maps set to distance blend instead of fog, desn't have the same problem with opacity, but means you have to put the falloff map into every material in your scene, which could be teadius in some cases.
Toxic Frog
06-08-2004, 02:26 PM
Cullen - I'm hoping I won't have to resort to this, cause I've got 6 individual scenes with this problem. UGH. But like you said, if ya gotta, ya gotta...

jbrophy - this is odd, because the 'exponential' setting actually fixed another scene. The only real difference between the two is this: The scene where it worked has dark fog, and the scene I'm currently wrestling with has light fog (snow scene). I wonder if that has anything to do with the exponential setting's effect?

gjpetch - Now I need to decide which is more of a pain, your work-around or cullen's... :)

I'd still like someone to reply with a solution that will apply directly to the rendering, without any post work. I've talked to several people who have had this problem (and found many messages online about it as well), so it's pretty common. I know a lot of us would love a good solution for this annoying feature.
gjpetch
06-09-2004, 12:17 AM
Cullen's sollution is probably less of a pain, but will still give you artifacts if you have multiple overlapping opacity mapped objects. Wish there was a better solution to this.
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