Rigid Polygon Tool
Activate the tool, then select consecutively at least three existing points (or click at least three distinct positions in the Graphics View) which will be the vertices of the rigid polygon. Click the first vertex again to "close" the polygon.
The generated polygon will display in the Graphics View only two of its vertices: one can be dragged to move the polygon in the plane, and the other one allows to rotate the polygon around the first vertex. The polygon will keep its shape and size.
Holding down the Alt (MacOS : option) key after selecting a vertex of the rigid polygon creates the next vertex such that the side between these two points makes with the preceding side an angle that is a multiple of 15°.
