Decals - Lost on how to

Autocon

First let me say hi, my name is Anthony and I'm a student in Game Art and Design. Been a big fan of the polycount forums, read them often and have learned a lot.

Anyway my question is how exactly do you make decals. I have read all over the place that you should use decals for things like graffiti and what not to save space on your UV's you wish to tile to break up the monotonous tiling of them.

I have taken a few texture classes in school now but they have never gone over anything about decals at all. So for projects I havent been tiling really any textures because if I want to have graffiti on a wall it would tile that graffiti all over the place. Basicly I have just fully textured each side of objects which hurts details I can have in large objects such as buildings.



Now I know you can do decals in editors like unreal but I havnt taken a class in unreal yet. It also seems that for nice polished renders people use decals in max or maya.

If anyone could point me in the right direction I would greatly appreciate it

Thanks a ton in advance,
Anthony

Tumerboy

You can use Decals wherever you want. (your engine may disagree with that statement)

Basically, it's just a piece of geometry, floating just above the surface you want it to look like it's part of, and then textured to be what you want.

So for instance, with grafitti. If you have a wall that is a single quad, your grafitti would probably be a smaller quad placed where you want the grafitti on that wall, and offset (in front of) from the wall by a small amount. (small amount depends on the scale of your scene, but usually .25"-.5" is ok. You then give it a texture that looks like the graffiti you want, UV it to that piece that's floating over the wall, and make sure it's got alpha around the edges of the texture. Often with something like grafiti, you'll want the painted area to be semi transparent so you see some of the underlying wall beneath it. This also very much depends on the decal you're making, I'm only speaking for grafitti right now.

Hope that makes sense.

For more complicated shapes, say your wall is polygonally bumpy, you'd want to duplicate the faces of the are you want the grafitti, ofset those polys slightly, and UV it to your texture.

Many times, a flat quad will work for your decal, but it all depends on the complexity of the underlying surface.

Hopefully that helps some, if that's still confusing, I'm sure one of the trolls around here will tell me how wrong I am :P