It's not to replace some optimized grass system , but more some fast tool "object palcement" painting.
Paint and place trees, rocks with some random Y rotation and some random scaling for example.
Automatically place some object oriented to the normal of the terrain or floor, it would be automatcially well oriented on top of terrain or floor.
Some options would be usefull also :
- Y random rotation
- Min-Max random scaling
- Y offset (Min , Max, random ) values , for example trees should have their trunck down on ground in Y axis.
This is not the best example and more advanced, but it shows the idea