God Rays

Pookhan

Hi all! I am developing a game at Dare to be Digital. It's an iPad game and we are using the Unity engine. It is set underwater and I am having trouble making convincing god rays.

Does anyone have a good technique for making them with 2d planes, instead of dynamic lighting?

Thanks in advance,
Pookhan

JamesWild

As far as I know the God Rays in UDK are done by drawing the area around the light to a low-res buffer, then repeatedly drawing it at different locations/scales so it makes a nice blurry ray. At certain settings you can see the separation.

Pookhan

The trouble I'm facing is that the iPad can't handle transparency very well. Or dynamic lights for that matter. So using 2d planes will have a lot of alpha and will bring our frame rate right down. Unity has a feature for making light shafts but it uses dynamic lighting so would kill the iPad too.

JamesWild

It'd be additive blend which is usually a bit cheaper than alpha blend.

The overdraw would be killer, yeah, but if you want dynamic god rays, there's not really any other way.

Your only real other choice is modelling them, which'll be completely static.

Rick Stirling

Most games use a variation on this technique:

http://http.developer.nvidia.com/GPUGems3/gpugems3_ch13.html

You render into a small buffer (1/4, 1/8th) and then apply a radial blur.

Pookhan

Cheers for the advice lads. I'll keep working on it and hopefully get it looking nice.

Feel free to follow us on twitter @dare2012_lazzyb

kio

i guess your best bet is to do something like james wild suggested.

might be a good read for you too:

http://blogs.unity3d.com/2012/03/23/shadowgun-optimizing-for-mobile-sample-level/