Cool thankyou , I applied in the end the color range technique and I was surprised that even if I got many pixels out the texture decal itself blended enough well on the terrain details at least I think so .... Sorry for making too many threads I ll make just one next and post n the suggested place ...
One possible approach to create scattered debris decal textures with perfect masks normals and ao (even diffuse and specular if you go to that extreme) all in one go, would be to model them out then render to texture using a technique Slum went over in the Best workflow for gravel-roads? thread. It's a lot more work up…