| controlID | The control ID for the handle. |
| position | The position of the handle in the space of Handles.matrix. |
| rotation | The rotation of the handle in the space of Handles.matrix. |
| size | The size of the handle in world-space units. |
| eventType | Event type for the handle to act upon. By design it handles EventType.Layout and EventType.Repaint events. |
The function to use for drawing the handle e.g. Handles.RectangleCap.
Custom CapFunction has two responsibilities:
1. For EventType.Layout event, call HandleUtility.AddControl to inform Unity about the distance of the handle from mouse position.
2. For EventType.Repaint event, render the actual handle.