Ivan wrote SketchPad which introduced a half dozen
or more wonderful concepts to the field of interactive
computer graphics. AlanKay once asked Ivan how he had
been able to solve so many hard problems so early.
Ivan replied that he
just didn't know that they were supposed to be hard.
For his pioneering and visionary contributions to computer graphics, starting with Sketchpad, and continuing after. Sketchpad, though written twenty-five years ago, introduced many techniques still important today. These include a display file for screen refresh, a recursively traversed hierarchical structure for modeling graphical objects, recursive methods for geometric transformations, and an object oriented programming style. Later innovations include a "Lorgnette" for viewing stereo or colored images, and elegant algorithms for registering digitized views, clipping polygons, and representing surfaces with hidden lines.