Fake volumetric light

VPrime · Jul 2010

Hey guys, I am trying to make a fake volumetric light effect (for a flash light) tow ork with an iPhone game..
I can't figure out a good way to go about this.

I tried to make 2 planes and have them cross like this:

     |
  -------
     |

But that doesn't look to great... I can clearly see the crossing in game.
here is a screenshot of how it looks ingame..

Does any one have any ideas on how I could create a nice looking fake volumetric light?

mortalhuman · Jul 2010

Do, like, a cone shaped cylinder, then delete the end faces or map those with your transparent part of your image, and once you map the cylinder part you can work with that to get what you need (probably best to fade the intensity as it goes out as to not see any borders at the end).

Basically, model the volume of the light in the cone that represents it. Hope I've helped.

Chai · Jul 2010

Well mortalhuman pretty much summarized the standard approach to it.

I was doing some reading into this very subject, and came across an interesting link .. I'd recommend checking it out as it's a nice detailed and visual explanation of this approach (in UDK) :
http://udn.epicgames.com/Three/VolumetricLightbeamTutorial.html

Edit: I also remember the two plane approach from many years ago, not as good as the cone one ... but if you wanna make it work - you have to make sure there's no shading on it, or it will give away the two planes. (try self illuminated, with alpha)

VPrime · Jul 2010

Ah thanks! Yeah I was doing the 2 plane thing from something I have seen many many years ago (quake 2 days I think?)

Cone method/the link is great thanks!

Carl Brannstrom · Jul 2010

You could also use several planes that always facing the camera, almost like a particle effect.
Might not have the optimal fillrate though...

Tumerboy · Jul 2010

Chai that's a good read. Don't suppose you have bigger versions of those Node layout shots eh? I can barely make out what anything is. . .

Neox · Jul 2010

corv wrote: »

You could also use several planes that always facing the camera, almost like a particle effect.
Might not have the optimal fillrate though...

have fun with the sorting

haiddasalami · Jul 2010

Tumerboy wrote: »

Chai that's a good read. Don't suppose you have bigger versions of those Node layout shots eh? I can barely make out what anything is. . .

If you follow the tutorial you should get something like that. Personally I have never been able to re-create that one but I used it as a building point to get what I wanted. Will send you pics or just send you the map file (pretty sure I saved it there)

Tumerboy · Jul 2010

Nah, not working in UE, trying to replicate the process in our engine. We currently have the shitty type of light beams that have hard edges etc. So I'm trying to correlate what UE calls something to what our engine does, and the tiny text for each box in the material set up doesn't help me.

THE 5 · Jul 2010

/industry outsider input
Why not just use 1 plane facing the camera?
The cone gives a better result when intersecting other geometry though.

Tumerboy · Jul 2010

because 1 plane facing the camera isn't 'volumetric' The whole point is to take up space, so that when viewed from different angles (heights, etc.) it looks like the light has shape and volume to it.

cman2k · Jul 2010

Ohhh, nice UDK link. I've looked at these sorts of things before but never truly understood how the effect was achieved...only parts of it. It's an interesting series of techniques and I love that it's all in one shader, no fancy in-engine tricks.

Nick we need to steal this shit, like yesterday.

Eric Chadwick · Jul 2010

Since you're on the iPhone, check out if you have vertex alpha support, it'll give a smoother fadeout along the cone than a texture would (and use less mem).

Beware though it'll probably cause sorting probs with anything else that's transparent in the world. iPhone's not much in the hardware dept.

Chai · Jul 2010

Tumerboy I'm afraid not .. I'd just use it as a guideline rather than a step by step guide.

Tumerboy · Jul 2010

Ya, that's pretty much what we're doing. The text doesn't cover some of the stuff I can see he's doing in the material layout though, and I can't figure out what is actually going on in there, i.e. he's doing a bunch of clamping on the blue channel, and then dividing the red channel by the square root of the blue channel???

arrangemonk · Jul 2010

blob cone + falloff as alpha - %of non vidibility and youre in

Fake volumetric light

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