A method includes displaying an on-screen ruler in a sketch area in response to a predefined input. The on-screen ruler has a first edge and an interior portion delineated by the first edge. The method further includes, in response to detecting a first touch input directed to the first edge of the on-screen ruler, rendering a line in the sketch area in accordance with the first edge of the on-screen ruler. The method further includes, in response to detecting a second touch input directed to the first edge of the on-screen ruler, adding fill content in a first portion of the sketch area that corresponds to regions touched by the second touch input on the touch-sensitive surface and that is delineated by the first edge of the on-screen ruler, such that the first portion of the sketch area is confined by the first edge or the line.