Sketchpad is the first graphic computer system invented by Ivan Sutherland. The user can interact graphically with the computer through different built transistors.
The surface of the picture becomes the window onto a depicted world. Alberti once said in one of his writings "On the Painting": “On the surface on which I am going to paint, I draw a rectangle of whatever size I want, which I regard as an open window through the subject to be painted is seen” )Alberti 1972. 55)