Paper #2 - Sketchpad: A Man-machine Graphical Communications System

Paper:
Sketchpad: A Man-machine Graphical Communications System
(Ivan Sutherland)

Summary:
The Sketchpad system is a system which allows a human user to interact with the computer by drawing lines on the screen. With the system, a set of buttons issue specific commands, switches activate functions, a light pen indicates position information and points to existing objects, and knobs rotate and magnify picture parts. Using Sketchpad to construct drawings serves as a model for the design process, giving the advantages of 1) storing and updating drawings, 2) gaining understanding of operations graphically, 3) serving as a topological input device for circuit simulations, and 4) producing highly repetitive drawings.

A hierarchal data structure is employed by Sketchpad, separating information of the general and specific parts of a drawing. This structure allows modifying details of the specifics without needing to change the general. Input is handled by a light pen, which serves a dual role of positioning new parts of a drawing and pointing to existing parts for modifications. Fairly extensive drawings can be achieved by its power of locking and tracking of picture parts through pseudo pen location and demonstrative language programs. Display is stored in a large input table, where magnification is handled by operating knows and geometric generation is computed with difference equations. There is an additional option to display modifiable abstractions, or user-desired properties, through circular symbols and numerical values.

Operations in Sketchpad are handled recursively with three very generalized functions in order to handle any fixed geometry subpicture: 1) expansion of instances (unlimited levels of subpictures for desirability), 2) recursive deletion (removal of all related subpictures from original deletion for consistency), and 3) recursive merging (combining two similar picture parts for complexity). The use of atomic operations for creating basic geometric objects thus makes it possible to create more complex geometric objects. One major feature in Sketchpad is the user’s ability to apply specific mathematical conditions on existing drawn parts. By defining a type of constraint for the computer to satisfy these conditions, a drawing can take the exact shape desired.

Sketchpad has been and can potentially be applied to various applications, ranging from producing patterns to artistic drawings. What Sketchpad hopes to achieve is the ability to make it more worthwhile to draw on a computer than by hand.

Discussion:
This is a paper about a system which allows a user to draw lines with a pen device on the screen and modifying those lines with a series of knobs, dials, and switches. That in itself, to a modern reader, is not too exciting. But for a paper written over four decades, that’s amazing and quite groundbreaking. Subjects covered in the paper such as precursors to graphical user interfaces and object-orientated programming are significant in themselves, but one of the things I find most interesting about this paper is how it is still easily readable.

One fault I did see with the technology presented in the paper is the light pen’s practicality as the dominant input device for computers had the mouse not existed. One advantage of the mouse that people take for granted is its ability to be used seamlessly with a keyboard without the user tiring much from prolonged use. The reason is probably because the mouse lies on the surface, so the user’s hand does not need to lift the mouse up for an extended time. That is not the case with the light pen. If the light pen were used in conjunction with a keyboard in a similar fashion as we use a mouse and a keyboard nowadays, I believe it would be far more tiring. Sketchpad's input system would have been a viable supplement to computers equipped with a mouse had it been economically feasible in its introduction, but it would not have been a successful substitute for it.

Since the paper was written, much progress has been made to touch/pen-based input with the Tablet PCs (covered to an extent in the Hammond paper in the previous blog post). But if the Sketchpad system had the success that the mouse had in that time period, a logical evolution would have been to incorporate a dual monitor system, one where the monitor stands up on the surface to cope with keyboard input, while the other would lie flat on the surface to cope with comfort in the same way as writing on paper does. In addition, I would have incorporated supplementary buttons on the pen, analogous to the ones found on the mouse.