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View Full Version : compositing / rendering brain-teaser

Arcon
07-22-2008, 02:31 AM
say you have a large hilly terrain model, one piece polymesh. i've got a rendering setup which is multiple shaders rendered out as different passes and comped later, which is easy enough. but imagine the camera is doing a flythrough between the mountains of the terrain model, how would i comp the different layers together...? some layers that are "on-top" in the compositing package should appear beneath at the same time if that makes sense, because they appear on a foreground and background hill at the same time.... what's the best solution to this...?

splitting the hills into seperate models is not a good idea, this is not for a film but realtime demo so i'll need a dynamic solution i can automate.
cshanks
07-22-2008, 07:42 AM
what about doing something with an inverted alpha in your compositing package? Just a thought.
misterdi
07-22-2008, 08:21 AM
Render a B/W matte pass, use it as matte for mask in comp.
Arcon
07-22-2008, 09:24 PM
how can i use alpha if its part of the same rendered object...? that's the problem.

for either of those solutions i would have to break up the terrain and/or assign a matte to a foreground hill... correct...? for this project that's totally impractical.... i need to be able to render any random shot anywhere on the terrain at any time as there are no storyboarded shots. so i can't spend time breaking up an area each time i'm asked for a shot.
CarlRiver
07-22-2008, 10:41 PM
If it doesn't have to be too accurate you could render out a zDepth pass and use that to generate a mask for splitting the mountains into foreground/background terrain.
Also the suggestion by misterdi sounds reasonable to me. With a b/w matte pass you have all the occlusion information needed to mask out unwanted elements.
Arcon
07-23-2008, 12:26 AM
thanks for the reply but i still don't think you understand the nature of the scene.... how do you do a B/W matte pass if the whole scene is one object...?
ytse77
07-24-2008, 03:39 AM
I don't get why your passes would need any tweaking at all... unless some of them have transparency? Maybe something like snow peaks on the tops of the hills that you want to composite later? If that's the case then I can see how a hill that's behind another would show up in one of those passes right through one in the front. Is this what's going on? Maybe some screenshots might help.

Good luck.
Arcon
07-24-2008, 06:35 AM
omg it was soooo easy lol. turn off visible in refractions, enable shader refractions & turn on raytracing, resulting render is transparent with alpha BUT the transparency areas won't show the surface that's behind itself :)
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