A convenient and natural way to draw polyline shapes on a stylus-based computing device is described. A tool or other drawing function relies on a timing mechanism to identify the various vertices in a polyline shape. For example, the endpoint of each line may be detected responsive to the user stopping (or substantially stopping, such as by remaining within a predefined maximum movement threshold) movement of the tip of the stylus relative to the touch-sensitive surface. In addition, feedback is provided indicating that a line and/or its endpoint is about to commit to the polyline shape being drawn. Such feedback may be displayed shortly before the line and/or endpoint actually commits. Upon further delay without substantial movement of the stylus, the line and/or endpoint may then actually commit. A “snap” function is also provided that assists the user in fully closing the polyline shape, if desired.