Canvas Spline Toys

I am pretty busy this week. For the past few days, I’ve been doing 8 or more hours of research, as well as packing and organizing my physical and virtual possessions. I hope to have several more posts over the next few days detailing some of the projects, medium and small, that I have worked on in the last few months.

The latest project is a simple interactive spline visualizer. I had a random itch at work to have a way of seeing splines constructed one-piece-at-a-time, so I created an initial mockup using the HTML canvas object. Eric Dramstad extended it with mouse support for rearranging control points, as well as cleaner code.

The blue line is a conventional second-order linear interpolation. From an OpenGL standpoint, it has the nice feature that the interpolated line lies entirely within the triangle defined by the three control points. The corresponding disadvantage is that the line does not pass through the second control point. The green line does the reverse. Instead of interpolating between L1(t) and L2(t), it interpolates between L1(t) and L2(-1 + 2*t). The green spline passes through all three control points, but is thus not nicely contained like the blue spline.

An interested programmer could extend this without too much difficulty. It would be particularly cool to be able to (A) add additional control points, and (B) interactively define new interpolation routines. Even without such features, Eric Dramstad’s interactive version makes for a surprisingly entertaining minute or two!

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