That surprises me, but ok. I think I have a use case which an industry wide issue. Screws tend to be small and accumulate dust very easily, especially if they don't stick out. I attached a real picture of an allen screw and a regular flat screw to illustrate this. You can see with the flat screw that dust accumulation is mainly height based.
There are generally 3 ways to add dust to the screw cutout:
-Use the AO map.
-Use the curvature map.
-Use a pre-made screw brush.
Unfortunately, none of them are a good option. Using the AO map is a hack it is not designed for. If the screw is near other geometry AO can be present anywhere, resulting in areas with dust applied where there should be none. Curvature sounds good, but it sometimes generates thin lines only at the edges (depending on the geometry), leaving the middle without dust. Using a pre-made brush is not an option in my case because I work with CAD data and all the screws are already build in the high res model. Re-painting it all can certainly be done, but it is unnecessary work if it can be automated.
-Using a height map in combination with a curvature map can make the look of dust in indented geometry much more realistic because it can simulate how real dust accumulation works. It starts at locations of high curvature and then extends further at places where less airflow and touch is present, which are areas of lower height.
I suppose a physics based particle brush can create a similar effect if it simulates the way real dust accumulates (curvature, airflow, obstructed), but as far as I know, no such brush exists, and I think it still needs a height map to function correctly.
