TR-131: An Efficient Window Based System Based on Constraints

Abstract

We describe the design of an efficient constrant-based window system for Smalltalk. This window system permits the specification of windows by constraining the subwindows to satisfy relationships from a very small number of primitive prioritized constraints. In fact, only three classes of constraints are supported, one of which is implicit and unavailable for general use. The system extends the current Smalltalk system by eliminating some of its existing inadequacies and by permitting the integration of both fixed-sized and scalable subwindows in the same window. A goal of the design is to produce a system with real-time response that is fast enough to be substituted for the existing design. A prototype with response times of less than 1/4 a second has been implemented to demonstrate the notions; alternative constraint satisfaction solution techniques are being experimented with to speed it up even further.