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Doing light shafts?

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I've watched several demoscenes lately and wondered how they do lightshafts in it. What I mean is that in those demos there's a very powerful light and some 3d geometry or clouds obscuring it, only that you're looking directly at those clouds and volumetric seamless light shafts stream through holes in those obstacles. I can think about extruding something like 'shadow volumes' for geometry, but how do they do that for arbitary textures-alpha masks?

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If anyone knows how to create shafts of light with textures, god, PLEASE reply here. The only solution I have right now (which isn't extremely practical for the application I'm focusing on) is using shadow volume-style model generation and displaying in a similar manner as volumetric fog.

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Quote:
Original post by Halo Vortex
I've watched several demoscenes lately and wondered how they do lightshafts in it.

What I mean is that in those demos there's a very powerful light and some 3d geometry or clouds obscuring it, only that you're looking directly at those clouds and volumetric seamless light shafts stream through holes in those obstacles.

I can think about extruding something like 'shadow volumes' for geometry, but how do they do that for arbitary textures-alpha masks?


There are presentation slides online for "Volumetric Light Shaft Rendering" here: http://www.ati.com/developer/gdc/Mitchell_LightShafts.pdf

I hope this is helpful.

--Chris

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Out of speculation, have you tried researching post processing pixel shaders? By setting up a triangle (shader applied) you could create some cool effects with light beams with the NVidia Shader Dev SDK.

I'm at a loss of how to explain how they did it in HL2 however ;)

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Quote:
Original post by chrisATI
Quote:
Original post by Halo Vortex
I've watched several demoscenes lately and wondered how they do lightshafts in it.

What I mean is that in those demos there's a very powerful light and some 3d geometry or clouds obscuring it, only that you're looking directly at those clouds and volumetric seamless light shafts stream through holes in those obstacles.

I can think about extruding something like 'shadow volumes' for geometry, but how do they do that for arbitary textures-alpha masks?


There are presentation slides online for "Volumetric Light Shaft Rendering" here: http://www.ati.com/developer/gdc/Mitchell_LightShafts.pdf

I hope this is helpful.

--Chris


*jaw drops* Wow, that's precisely what I was looking for! Thanks!

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Half life 2? Haha, its just a grid of 8x8 quads. The quads extend down and overlap each other in the grid pattern i was talking about. If you have "garry's mod" for half life 2 you can actually place these shafts of light and see what im talking about.
Hope that helps
-Dan

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Guest Anonymous Poster
i remember asking this question to someone from here a long time ago. he showed me a demo and explained how it worked, it was way over my head at the time but i think if he explained it again i could figure it out, i do not can't remember his name but i think it was sagely or sages (i know it had something to do with sage.)

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Guest Anonymous Poster
For realistic light shafts the volumetric fog kinda way is the way to go.. similar to the ati whitepaper.

But I think the in the "demos" they probably use some kind of (radial) blurring. I think one of Nehe's tutorial demonstrates it. You should check it out. This is very easily applied to arbitrary textures.

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