Sun shading devices provide an opportunity for the designer to control natural lighting, ventilation, and solar gain, all of which provide a benefit to the overall building performance. Through sun path diagrams and shading masks, some of the effects of these solar controls can be demonstrated graphically. This paper describes Shading Mask, a computer program written to help designers understand the basic theory of solar control; generate sun path diagrams; design overhead, side, and eggcrate shading devices; calculate solar angles and shading masks; and provide case studies of actual buildings.