Keep in mind that a shape does not know about bodies and stand apart from the dynamics system. Shapes are stored in a compact form that is optimized for size and performance. As such, shapes are not easily moved around. You have to manually set the shape vertex positions to move a shape. However, when a shape is attached to a body using a fixture, the shapes move rigidly with the host body. In summary:
- When a shape is not attached to a body, you can view it’s vertices as being expressed in world-space.
- When a shape is attached to a body, you can view it’s vertices as being expressed in local coordinates.