Boxes are base elements used in relations constraints. Relations constraints are mathematical operators that control animated objects.

For sample C++ code, see Code samples.

A box is a fundamental building block of MotionBuilder. All animatable elements derive in some way from the main box class (either by deriving directly or owning a box). An FBBox can be connected with other boxes, models, or devices.

By developing a box plugin, you can add new types of operators, sources, and converters to a relations constraint in MotionBuilder. Boxes developed with the SDK appear in MotionBuilder under /Plugins in a Relations constraint tool.