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View Full Version : Voxels clipping Fibers - help please.



JoePoe
02-27-2010, 03:14 PM
I've got some rolling hills with grass from Fiber FX. In the low lying areas I'm putting in some fog using HyperVoxel sprites (not liking the other fog options under volumetrics - although I have to say I haven't seen what Ray Marcher does, takes way too long).

Problem.... Wherever the voxels are, the fibers get clipped.

I've had the same object (the ground) drive both fibers and voxels, and I've used a separate emitter for the voxels. Same result.
(Also, fyi, the ground is being deformed with a displacement map. Not that I think that's doing anything to generate the conflict.)

Anybody?

jin choung
02-27-2010, 05:02 PM
I've got some rolling hills with grass from Fiber FX. In the low lying areas I'm putting in some fog using HyperVoxel sprites (not liking the other fog options under volumetrics - although I have to say I haven't seen what Ray Marcher does, takes way too long).

Problem.... Wherever the voxels are, the fibers get clipped.

I've had the same object (the ground) drive both fibers and voxels, and I've used a separate emitter for the voxels. Same result.
(Also, fyi, the ground is being deformed with a displacement map. Not that I think that's doing anything to generate the conflict.)

Anybody?

render separate passes and render the grass with a z-buffer and comp it.

jin

3dWannabe
02-27-2010, 07:11 PM
render separate passes and render the grass with a z-buffer and comp it.

jin

Jin - have you come across any "z-buffer compositing' tutorials?

I've heard the phrase mentioned many times, but haven't stumbled across anything on Google that really explains it - or how the Lightwave workflow is set up.

Also, do you need a compositor like Fusion to do that - or would AE CS4 work?

Thanks!

jin choung
02-27-2010, 07:22 PM
ae cs 4 would totally work (first step, check out ae help for z-depth-buffer).

hold one... lemme see if i can find tuts...

off the top of my head, you can render a separate depth pass inside of lw and then use that greyscale image (render at 16bpc or higher) as alpha mask (track matte or effects>channels>set matte) in ae....

ok, so found some tutorials but they make it seem harder than it is. just render out a zdepth channel in lw. open it in photoshop and just make sure it looks like what it should look like.

take it into AE and use it as a track matte or 'setmatte' and use luminosity as the input factor (instead of alpha). adjust things like sharpness or graininess of the mask and its volume by blurring or controlling brightness/contrast (will probably have to pre-comp the z buffer layer for those adjustments to take).

in that way, you can use the z depth values to control the density of the fog so that the closer you are to camera, the more invisible the fog - which should be the effect aimed for. this will account for the fog that intersects with the pixels of grass - you'll probably need to bring in a duplicate later of fog to account for the regions not accounted for in the depth matt.

luck.

jin

p.s. i'm assuming a kind of low to the ground camera raking the grass. if it's an overhead angle above the ground fog, larry's solution would be a helluva lot easier and faster.

although if you were hellbent on using hypervoxels or that alone generated the effect that you like, you can make your hills black and just intersect it with a white plane (both diffuse is zero, illumination is 100) and use that as a mask for your hypervoxels (which are again, rendered out separately).

SplineGod
02-27-2010, 07:30 PM
Do you have raytrace transparency turned on?
Also try doing he fog using geometry rather then HV sprites.
You can create a stack of polys, add a procedural texture in the transparency channel set to world coords. Vibrate the polys quickly with motion blur on. It can produce pretty good results quickly. Heres a couple of examples:
http://www.3dtrainingonline.com/examples/ground_fog.jpg
http://www.3dtrainingonline.com/examples/volumetrics_test.jpg

JoePoe
03-01-2010, 04:52 PM
Jin & Larry - thanks so much for the quick responses and suggestions. I will definitely give them a shot. Although i have to say, I'm going to have to read up on Z-buffering. I've seen it there in globals but never tried it :chicken:. As for the other ideas ..... very creative solutions!! I look forward to trying them.

And, Larry, yes raytrace trans was on. (worth mentioning in case someone else out there is wrestling w/ the same issue).

In the meantime... This whole while I've been considering this a voxel problem, and after spending TOO much time trying to work a gradient onto the voxels (opacity, density, dissolve etc.) I finally stumbled back over to the fibers and just by chance hit the "Volume Only" button and .... voila!!

I took a little hit on render times, but this is what i got....
(couple of test renders here. Not exactly the same files (thanks to a crash), but you can see what I was trying to avoid and what I ended up with).