A big advance in computer graphics during the 60's was to come from a MIT student named Ivan Sutherland. In 1961 he created a computer-drawing program named Sketchpad. Sketchpad allowed you to draw simple shapes on the computer screen, using a light pen, save them and even open them later. The light pen had a small photoelectric cell in its tip. The cell emitted an electronic pulse and whenever it was placed in front of the computer monitor and the monitor's electron gun fired directly at it. By simply timing the electronic pulse with the current location of the electron gun, it was easy to pinpoint exactly where the pen was on the screen at any given moment. Once that was determined, the computer would then draw a cursor at that location.
Sutherland seemed to find the perfect solution for a lot of the graphics problems he faced. Even today, a lot of standards of computer graphics interfaces got their start with this early Sketchpad program. An example of this is in drawing constraints. If you want to draw a square for example, you don't have to worry about drawing four lines perfectly to form a box. You can specify that you want to draw a box, and then tell the computer the location and size of the box. Then the software will construct a perfect box for you, with the right dimensions and at the location you want.
