A Graphics Toolkit Based on Differential Constraints

This paper is in the vein of the last one I posted, talking about a graphical toolkit called Bramble that also uses constraints. The author of the paper is Michael Gleicher and he outlines the main characteristics of Bramble, showing also what set it apart from other existing graphic toolkits of that time.  Being the big differences the fact that it uses a differential approach and the fact that it allows non-linear constraints, such as distance and orientation, in addition to simple connections. The paper can be obtained through the following link:

http://www.cs.wisc.edu/graphics/Papers/Gleicher/CMU/uist.pdf

Bramble uses a differential approach, in which constraint techniques are used to support direct manipulation i.e. interactions where objects move with continuous motion that are coupled to the user’s actions, such as dragging.

The differential approach used in Bramble aims to provide more flexible methods for the manipulation of graphical objects by permitting constraints and controls on aspects of objects, rather than just directly on their parameters, and permitting these constraints and controls to be combined. Allowing graphical objects to provide the positions of points as outputs without knowing what will be connected, and interaction techniques that can be defined in terms of point positions, without knowing what types of objects these points come from.

The differential approach also permits users to control how combinations of aspects evolve over time, being that aspects can either be driven towards a particular value, or forced to follow a moving target. Those basic differential interactors serve as building blocks for interaction techniques. More complex differential interactors are created by rules which switch a basic interactor on and off as needed. The range of interaction techniques results not from extending this set, but rather from the aspects to which they are applied and how they are switched on and off.

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