The important thing for the decals is that you can't only have rectangles but also quadrangels (i need that for another function).
The whole terrain is much to big to apply a single decal texture on it. And it should be possible to have transparent decals. So you can't put the texture on the triangles it affects because you wouldn't be able to see the textures that are under the decal.
The whole terrain is much to big to apply a single decal texture on it. And it should be possible to have transparent decals. So you can't put the texture on the triangles it affects because you wouldn't be able to see the textures that are under the decal.