Reading 4#: Sketchpad A man-machine graphical communication system

Comments:
Wenzhe Li
Summary:
The paper is a detailed introduction of Sketchpad.

The design of Sketchpad is based on a ring structure, which makes it easy to find the next and the previous member. Then, it introduced how it works. How to display, such as display lines, circles, digits, text and so on. Some general recursive functions are very important in the Sketchpad, such as expanding, deleting and merging. All these functions are to operate all related elements recursively.

An important idea in the Sketchpad is the "copy" function, which makes drawing more easily. However, the disadvantage of copy function is that it can only copy a instance as a whole. Besides, another core of Sketchpad is constraint satisfaction, which is far more different with pencil and paper. Users can design some constraints for their drawing and make Sketchpad satisfy. It can help users draw very easily.

At  that time, Sketchpad can used for linkage, bridge design and drawing, except electrical circuit diagram.

Discussion:
Generally speaking, Sketchpad was a milestone at that time. I cannot imagine such a machine could be designed. Sketchpad, was equally important with the first computer, in my opinion. It seems a ancestor of several design software, like CAD, Pspice.  And it is also the ancestor of Sketch Recognition.

I am very impressive of its function about constraint satisfaction. I think it is the most important feature of Sketchpad. Even someone who is not good at drawing, can draw a beautiful picture through setting up some constraint and making Sketchpad satisfy. Drawing is not as difficult as before.