HotDraw (abstract)

HotDraw is a framework for structured drawing editors that has been floating around the Smalltalk community for several years under several incarnations. It was originally developed by Kent Beck and Ward Cunningham, but has been reimplemented many times since then. Most of these implementations were proprietary. Our design extends the original one by making constraints more composable and by adding metafigures, but the system is instantly recognizable by anyone familiar with one of the earlier implementations. We wrote a version of HotDraw for ObjectWorks\Smalltalk Release 4.0 that we are distributing. We will describe and demonstrate the basic framework and several applications built from it, such as a visual programming language, a tool for inspecting Smalltalk objects by drawing pictures of them, an environment for learning Smalltalk by issuing commands and writing scripts for visible objects, and a PERT chart editor. These applications illustrate several advanced Smalltalk techniques, such as light-weight classes, compiling code on the fly, and dynamically redirecting messages by overriding doesNotUnderstand:. Time permitting, well explore the implementation of HotDraw and how it uses these techniques.