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Date: Tue, 10 Dec 1996 03:26:02 GMTServer: NCSA/1.4.2Content-type: text/html<html><head><TITLE>The SkyBlue Constraint Solver</title></head><body><H2>The SkyBlue Constraint Solver</H2><p>Author: Michael Sannella<p>Published as UW Tech Report 92-07-02.<P><hr><H3>Abstract</H3>A constraint describes a relationship that should be maintained, forexample that the equality A+B=C holds between three variables, that a setof displayed objects are aligned, or that the elements in a data structureare consistent with a graphic display of this structure. Constraintsolvers have been successfully applied to problems in computer graphicsincluding geometric design and user interface construction. This paperpresents the SkyBlue constraint solver, an efficient incremental algorithmthat uses local propagation to maintain sets of required and preferentialconstraints. SkyBlue is a successor to the DeltaBlue algorithm, which wasused as the constraint solver in the ThingLab II user interface developmentenvironment. DeltaBlue has two limitations: cycles of constraints areprohibited, and the procedures used to satisfy a constraint can only have asingle output. SkyBlue relaxes these restrictions, allowing cycles ofconstraints to be constructed (although SkyBlue may not be able to satisfyall of the constraints in a cycle) and supporting multi-output methods.The SkyBlue algorithm has been incorporated into Multi-Garnet, an extendedversion of the Garnet user interface development system that supportsmulti-way constraints. Multi-Garnet has been used to build several userinterfaces exploiting the features of SkyBlue that would have beendifficult to build within Garnet. This paper describes the basic SkyBluealgorithm and outlines several techniques that significantly improve itsperformance for large constraint graphs. Performance measurements arepresented demonstrating that SkyBlue is efficient enough to use ininteractive user interfaces.<P><HR><P>Click <!WA0><a href= "ftp://cs.washington.edu/tr/1992/07/UW-CSE-92-07-02.PS.Z">here</a> to get the postscript file.<P>Return to <!WA1><a href="http://www.cs.washington.edu/research/projects/weird/www/index.html">Constraints home page</a>⌨️ 快捷键说明
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