Actor: User

Purpose: Draw a polygon's vertices and edges.

Overview: A user "draws" a polygon by picking the vertices. The system draws the edges between them.

Type: primary and essential

Cross References: N/A

Typical course of events

Actor Action

System Response

1. This use case begins when the user indicates that she wants to add a polygon to the current
picture.

2. Indicates that the current function is "draw a polygon."

3. The user selects the position of the polygon's first vertex.

4. Displays a visual marker at the position of the polygon's first vertex.

5. In sequence, the user selects the positions of each remaining vertex.

7. The user indicates that the polygon is finished.

6. As a vertex is selected, displays the edge between it and the previous vertex.

8. Displays the edge between the last and first vertices.