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Sneak Peek of Constant-Width Strokes in Freehand Drawing Library

November 7, 2011

The full 1.0 release of the Freehand Drawing Library will contain classes for both fixed- and variable-wdith strokes.  The latter was the most challenging in terms of implementation, so it was the first entry into the library.  Now, my attention is turning towards constant-stroke classes.

Unlike its fixed-width counterpart, I anticipate a wide variety of both algorithms and stroke styles to be employed with fixed-width strokes.  In order to avoid bloating the library with one class for every conceivable type of fixed-width stroke, a different architecture is used inside the library.

A BasicStroke class that implements IFreehandDrawable was created that serves as the constant-width counterpart to the Freehand class.  Both fixed- and variable-width stroke classes accept the same data providers.  To accommodate a wide variety of fixed-width strokes, the StrokeDataVO now contains a reference to a drawing engine of type IDrawingEngine.  The fully qualified class name of the IDrawingEngine implementation is assigned before setting the data provider for a BasicStroke.  This engine performs the actual drawing while the application interfaces with an IFreehandDrawable instance.  The application is thus agnostic to both fixed- and variable-width strokes.  A Factory may be employed to return the desired type of stroke based on input properties.

The basic drawing engine is based on simple line segments, i.e. point-to-point.  Although occasionally useful, this engine (net.algorithmist.freehand.engine.LineSegments) is intended to serve as a base class for other engines.  A smoothed-stroke engine is currently under development,  net.algorithmist.freehand.engine.SmoothedStroke .  It uses the same smoothing algorithm as the variable-width Freehand stroke, but without the overhead for computing the two splines used to vary stroke width.  A screen shot is shown below.

Lang Simplification, discussed in the previous post, should be useful for strokes containing a significant number of straight or nearly-straight sections, such as the rough ‘4’ in the above example.

The drawing engine may be changed during runtime simply by altering the engine reference and re-assigning the stroke data provider.  The new engine is applied to all subsequently drawn strokes.

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