The vertices defining a primitive can be moved, added and deleted using the image editor. Clicking on a selected primitive will enable point editing for that primitive. A primitive in point edit contains a green skeleton which connects its vertices. Representing each vertex point is a hollow green square or point handle. The currently selected point is shown by a blue point handle.
To move a point, select and drag the appropriate point handle. To delete a point, select its point handle and use the "Edit/Delete" option (or press the "Delete" key). To add a new point to the primitive, click on the green skeleton and drag the mouse. When the mouse button is released, a new point is inserted between the indicated vertices. If objects are currently being snapped to grid intersections, points being moved or added will also snap to grid.
To leave point edit mode, click on the background or another shape.