Apple Motion 3 - Manual (Page 1005)

Chapter 12 Using Shapes and Masks 1005
 Press C to close the shape, joining the first point you created to the last.
 Press Return to finish an open shape at the last point you made.
 Double-click anywhere in the Canvas to define the last point of an open shape,
creating a line with a default width of two pixels.
Note: You can press Esc at any time while drawing a shape to cancel the entire
operation and delete the shape.