Dynamic Bezier Spline Scroller With Source

Paul Taylor and I collaborated on a TinyTLF demo for 360|Flex last fall that used a quadratic Beizer spline to form left and right vertical constraints for dynamic text layout.  After the demo, a few people said it would be really cool to see the text scroll.  The idea scroller, however, should be organic to match the text boundaries, just as a vertical scroller matches a straight-line text boundary.  Since the spline boundary is dynamic, this means the scroller track and thumb should be dynamically drawn.

Since I had some time, I took on the task to create another demo for Adobe MAX 2010 and it was completed during the conference.  I envisioned a possible TechNote on the scroller’s construction, but time constraints have since rendered that idea impractical.  Since a TechNote implies open-sourcing the code, the next best solution is to just open-source the code.  If there is sufficient interest, I might do a deconstruction over the course of several blog posts.

Now, the track is the easy part since we already have the constraint and the quad. Bezier spline is one that I released in Degrafa.  It’s a simple construction with G-1 continuity and a tension parameter.  Additional artificial tangent control is provided by augmenting the spline with degenerate quad. segments at the beginning and end.  The spline is non-interpolative.

Most of the details are in the thumb construction and update.  This demo uses a relatively simple arc-length parameterization based on adaptive interpolation, and the interpolator may be injected.  Two interpolators are provided with the demo, but I’ve only tested one.

The scroller uses a linear model to map thumb position to [0,1] for the thumb value.  I don’t like the linear model since it has some issues, so I sketched out a quadratic model, but did not have bandwidth to test the implementation.  I also did not have time to test every conceivable path through the code, so there may be a bug or two yet to be uncovered.  So, check it out and see if you can come up with some interesting ideas for using this in an application.

Yes, that’s a pretty ugly-looking demo 🙂  Your job is to turn it into something visually impressive.  Good luck!

View (Flex 3) Demo

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The companion demo illustrates how to use two of the Bezier splines to bound the width of an element.

View (Flex 3) Demo

View Source


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