This tool adds texture to the area around it by either “roughening” or by creating a
“sprayed” effect by randomly spraying paint over the surface.
To use this tool, just hold the left mouse button down and drag.
To change the tool width and effect level (strength), use the width and level entries on the toolbox. This tool is pressure sensitive when using a graphics tablet; the pressure varies the intensity.
Options
Roughen
This mode “roughens” the area around it. It can be used create the rough look of the
sands of a desert, the floor of a building, an unfinished wall, the leaves of a
distant tree - just about anything rough. You can set how much roughening to
apply by setting the tool effect level, and the size of the tool’s tip by
setting the tool width.
Spray-gun
This mode sprays paint over a surface, an effect that, in
combination with the smoother, may used to draw perfect-looking clouds or smoke. The mouse button you use dictates the color; the width and effect level may be set via the toolbox. The tool also takes
into account the alpha #1 setting. An alpha of 0 gives the most visible
dots and 255 the least visible dots.
This tool adds texture to the area around it by either “roughening” or by creating a
“sprayed” effect by randomly spraying paint over the surface. 
Roughen
Spray-gun