What you should see after adding a few points:

- The axis-aligned bounding rectangle of all the points, drawn in solid light blue.
- The convex hull of all the points, drawn in dashed green, and highlighted if the cursor is inside it.
- The (possibly concave) polygon defined by all the points, in the order they were added, drawn in solid red, and highlighted if the cursor is inside it.
- The two eigenvectors, drawn in solid light blue, centered at the centroid of all the points. The longer one is the first principle component.