Move a shape using the flow of a vector field, as measured at the centre of the shape bounding box.

Input parameters:

1. Sh → Shape to move.
2. Fl → Field exerting a force on the shape.
3. Mt → Motion type.
   • 0 → Step
   • 1 → Flow
   • 2 → Trajectory
4. St → Motion strength. Single Step scales the field vector by it, Integrate reads it as the duration of the flow, and Trajectory reads it as the length of the trajectory. Negative values move the shape upstream.

Output parameters:

1. Sh → Shape moved by the field.
2. Tr → Motion transformation.