Unreal: Opacity influenced by object intersections (Bioshock waterfall example)

nick!

This one is for the Unreal guys. Does anyone know what shader setup was used in this Bioshock video where the Big Daddy steps into the sheet of falling water? The water itself just looks like a plane with its opacity influenced and masked out based on where the Big Daddy collides with it. It's something I've been interested in setting up for a while now but didn't know how to approach the shader. Any help is appreciated.

Also, there seems to be a secondary effect where splashing water particles are generated at the areas where the big daddy intersects with the water plane. This isn't as important, but if anyone knows how to set this up, I'd be itnerested. Thanks for any help you can provide.

JordanW

It's called depth biased alpha, there should be a node for it. Basically run your opacity maps/instructions through it's alpha input and give it a bias for how thick the intersection should be.

nick!

Thanks for the reply, but that's not the effect I was referring to. I'm familiar with handling smooth/soft transitions between intersecting translucent planes using the depthbiased node.

If you watch the video, the effect I'm after is where he intersects the water plane and everything below the points where his geometry and the water plane geometry collide get masked out in the water's opacity. It's faking the effect of blocking the water from falling where his body blocks its path, but it's not a particle effect since the opacity effect changes immediately when he moves (there are no residual particles falling as he moves around) and there's occasional flickering when his geometry just skims the surface of the water plane.

JordanW

ah my bad, i would have to say that may be chalked up to some of the custom programming that went into their water system. I think they claimed that had 1 artist and 1 programmer working solely on water systems for a year.

gamedev

They have a pretty custom build of UE3 at this point. Nonetheless, there is some bad flickering if you really watch. Looks to be all smoke and mirrors / or a really cool water tech implementation. Or maybe a custom particle effect w/ collision on, duped a few times? Looks pretty sick either way.

Edit - Jordan beat me to it.

ColinR

I believe there's a PDF out there where two of their tech artists have described how they dealt with a lot of the water issues they were having during development and their workarounds.

ColinR

http://www.2kboston.com/powerpoint/The-Art-and-Technology-Behind-Bioshocks-Special-Effects.zip

It's all there, and a good few pages on interactive waterfalls. Hopefully it helps you nick! in some way.

Remember you posting up your showreel a good while back as well, was great stuff.

nick!

Thanks a bunch for all the replies. The doc ColinR posted explains it, but the custom nature of the effect and time constraints means we probably won't get it in. Too bad, but getting to peek behind the curtain and see how they achieved it is cool.