Autodesk Mudbox 2013 SDK Documentation > Sculpting and Brushes >

# Writing Brush Plug-ins

Brush plug-ins are written by writing classes which derive from BrushOperation. Most virtual functions of BrushOperation have default implementations, except for the following member functions, which must have concrete implementations provided:

- BrushOperation::DefaultStrength() - The default strength value.
- BrushOperation::AddPatch() - Called when a new surface point has to be added to the stroke.

When a plug-in derives from BrushOperation it will be automatically be made available for the users from the tools tray.

The strength is used to determine how much the sculpt tool affects the surface. The actual strength passed by Mudbox to the functions BrushOperation::AddPatch() and BrushOperation::Flood() is controlled in part by the fall-off data curve BrushOperation::FalloffData().