Sorry full of random ideas today it seems. This is an old idea I had which might be a cool system for FF. I picture this used mostly for particle and noise controls.
What about a set of tools that 1) allows a 'spawn' point so that particles or noise originate at that point and are drawn out in a user selected arc and distance and fade ie 0 45 90 etc? The other two tools would be a 2}repulse tool, to place locations that 'repulse' drawn objects in a user selected arc (like a force field) and range from the location of the tool and 3) the reverse a pull or magnetism type tool that would pull objects closer and cause them to bunch or clump with a user set distance and arc of effect.
So you could perhaps 'attract' dirt or grass to be drawn more clump more in an area of texture or use the 'repulse' to 'protect' an area of texture you don't want objects to be drawn to heavily on on and spawn to draw flames or smoke or fake light from a specific area,
Hastily drawn graphic during my lunch break which hope helps to clarify. Back to work ...