Have any of you ever made a fighting game where the fighters got bruised and/or cut? If so, how did you implement the bruising and cuts? Did you modify the fighters' body or face textures, and exchanged them after some conditions are met? Or is there some other kind of system out there? I'm wondering, because I'm making an MMA game, and I'd like for the fighters to bruise after a certain number of hits. This is my first time doing something like this, so I don't really know how to go about it.

Bruises are mostly local change in skin color, which can be done with decals quite convincingly. Cuts and blood likewise (you'll probably want to modify normals here too, and maybe add some particles for blood drips, etc). You can use volumetric decals if you want to simulate swelling as well, but I think that's kind of overkill.

Finally, if you want torn out limbs, you can use CSG techniques as was described in one of the GPU gems books some years ago for a zombie shooter (I forgot which book, and the name of the game, maybe I'll find it...). That one basically simulated torn off limbs and blast away body parts with spheres that were attached to the skeleton and a fragment shader that discarded fragments that would lie inside a sphere.

Thanks, everyone! I will definitely look up using decals for this.

If you aren't already considering it, it would be great if the injuries affected your ability to fight. instead of traditional health bars, you could have it so leg injuries affect your movement and ability to kick, and arm injuries affect your ability to punch or block, enough hits to vital body parts is a KO? Would be more complicated but fun and more realistic...

I've already planned to do something like this in the game. When the stamina is low and the health is low (this will be affected by the number of punches and kicks), the player (and the enemy) will visibly be slowed down and punches and kicks will lose their accuracy. I could also use this with injuries to the arms and legs, also. Thanks for the idea!!