Click on empty space to add a point. Click and drag on a point to move it.

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.