The present disclosure provides a passive light stylus that produces a defined intensity profile detectable by a user input device when at least a portion of a tip of the stylus is proximate an input surface of the user input device. In some embodiments, the stylus includes a housing including an entrance aperture configured to collect ambient light and an exit aperture configured to emit the collected light, where the exit aperture is proximate a tip of the stylus. The stylus also includes a light guide disposed within the housing, where the light guide is in optical communication with the entrance aperture and the exit aperture such that the light guide directs collected light from the entrance aperture to the exit aperture.

Output of a computer system is manipulated using a physical object disposed adjacent to an interactive display surface. A painting application produces an image in response to an object disposed adjacent to the interactive display surface. During each of a plurality of capture intervals, a set of points corresponding to the object is detected when the object is disposed adjacent to the interactive display surface. An image is projected onto the interactive display surface representing the set of points and is filled with a color or pattern. As successive sets of points are accumulated during each of a plurality of capture intervals, a composite image is displayed. An object can thus be used, for example, to "draw," "paint," or "stamp" images on the display surface. These images manifest characteristics of the object and its interaction and movement relative to the interactive display surface in a realistic manner.