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View Full Version : Can I bake volumetric lights?



Johnny
01-25-2005, 08:11 PM
I have a heartbreaking decision here: my scene looks GREAT with volumetrics thrown onto spot lights I have for a table light, but the render time with volumetrics is 7 times that without...

I suppose I can lower the quality, but can volumetric lights be baked? I don't see a trace of this anywhere..

Using 7.5D

thanks

cgbloke2004
01-25-2005, 08:42 PM
thats pretty much a no..
i think..
at least ive never thought it was and have always sought ways around it.

2 ways:

1) you could replace the volumetric light with a geometry based solution. this was the old way of faking volumetric lights. look for light beam in the classic content folder, and you'll see one made with the grid procedural, its quite convincing [if it ever comes face on to the camera you can ramp up a lensflare to help hide it and suggest the flare out you get when someone shines a bright torch at you] - i think its in the blade runner folder.

2) do the render in two passes:
a.) render your scene as normal, but turn off the volumetric light.
b.) then in a second pass, turn all your objects to black [done either in object panel or in surfaces - its just a quick thing anyway], turn off all non-volumetric lights and just render the whole scene with only your volumetric lights turned on.
[so you render out a black image, with only the volumetric light/beam visible]
composite the volumterics over the top of your first render.

i usually do a mix of the two above - far off beams etc, that youll never get near, i just use the fake beams - no render hit, and for near ones, or ones i want to be truly volumetric i render two passes and composite them. [since i'd be adjusting the whole thing in post anyway - works the same with animations]

hth

Johnny
01-25-2005, 09:04 PM
thank you..that geometry solution sounds worth investigating.

J

starbase1
01-26-2005, 06:21 AM
It's well worth mucking around with Viper for this kind of thing. I ran head on into it when a bunch of us were working in the 'Lets build a nebula' thread...

Viper will run pretty much proportionally to the render time, so you get near instant feedback on how you are doing.

You don't say what the actual texure function is that you are using, but this can make a big difference, so if you are just after a bit of random variation, try different patterns. You can also get big benefits by rediucing the number of octaves. If you need fine structure, then a higher small scaling parameter (nearly one) and fewer octaves is often a quicker way of getting the same effect. Self shadow also cranks up render time.

Check the number of slices if relevant too.

Nick