Thanks for the compliments Wjbender

Yesterday I started working on decals:

There are still some shading issues and they are too slow to create and have too much overdraw, but other than that it works great .

Edit: MOAR blood!

that's not even remotely enough blood!

(nice feature!)

oh, one thing I forgot to ask:
instancing possible? :3

How do you create the decals?

http://blog.wolfire.com/2009/06/how-to-project-decals/

@mk_1: it's interesting but to me it seems like it's pretty complicated / slow...

I think there are better methods to do this.

It is slow, yes. Should be used for static geometry only but then it's a pretty good technique because it's independent of the used rendering technique.

Well, while creating/changing decals is kinda slow (although can be quite fast if the meshes have their own acceleration structure like an octree) it works very stable and compared to alternatives in a forward renderer it is very fast to render such a decal once it is created.
Also it was actually very easy to implement. Just looping through faces and throwing everything away that is not needed. And cropping what is left, but thats also just some basic maths.

Hey guys, remember this awesome blogpost series we had about weekly updates and shit? Well, it's back!

This week it's about editors and decals. Surprising choice of topics, isn't it?

Question that always comes to my mind when I read Dave Rosens post about their decal implementation (and I do so very often) is how the whole thing is supposed to work with skinned meshes - as far as I understand it, it's simply a scene node attached to another scene node, with geometry built from cropping intersecting faces. So these faces have to be skinned, too, don't they? Also, as you write you take ALL meshes in the scene into accout when creating the decal mesh, what if you move the scene node that the decal is attached to? Wouldn't that create some rather ugly artifacts when the decal moves with its parent node?

Skinned meshes: Currently decals will kinda break with those. I mean yes, one could also skin the decal vertices, but then I would also have to create custom skeletons for the decals consisting of all bones of the skinned meshes covered by the decal (or only the needed ones, but then with custom animation frames and shit), also it is not really clear if such a decal should then stay the same and just move with the geometry or has to be projected again. Projection would probably be much easier, but also look wrong in most cases. The alternative to skinning the decals would be use CPU skinning for the vertices with the decal attached and update the decal for those. Would probably be the best solution, but still has the tricky part with projection vs following the movement.
I won´t touch this for now and would use a specialized solution for such cases like just modifying the texture of a character or something.

The decal actually is not attached to any scene node (unless you make it a child of something), instead it is just a scene node itself, can be moved freely and will effect everything in its range. Now if it is attached to another scene node and moves with it it again will effect anything in its range. So if this is not wanted, you will have to make sure it is not bigger than the scene node it is attached to.