cardinal曲线JS算法和demo

Cardinal spline =============== A `curve()` (cardinal spline) extension for HTML5 Canvas (JavaScript). This library extends the 2D context with a new optimized `curve()` method to enable drawing of cardinal splines - splines that goes through the defined points. The method is passed a simple array of points and a line is drawn through them at given or default tension and segment resolution, open or closed loop.  *Not to be confused with Bezier splines which uses end points and one or two control points, whereas the line is drawn somewhere between. With a cardinal spline the smooth curve goes through every point defined and you can have as many point as you wish in a single spline.* Usage ----- Make sure the script is loaded before a 2D context is retrieved from the canvas element. **Example** ctx.moveTo(points[0], points[1]); // optionally move to first point ctx.curve(points); // add cardinal spline to path ctx.stroke(); // rasterize path will draw the points in the array which is arranged in this manner: [x1, y1, x2, y2, ... xn, yn] Optionally a tension value can be given *(default: 0.5)*: ctx.curve(points, 0.5); // set tension [0.0, 1.0] +/- as well as a segment resolution value *(default: 20)*: ctx.curve(points, 0.5, 20); // points in each segment The curve can also be drawn closed. All arguments must be given in this case *(default: false (open))*: ctx.curve(points, 0.5, 20, true); // make a closed loop The methods returns an array with the spline points which can be used for tracking, calculate length and so forth: var splinePoints = ctx.curve(points); License ------- Released under [MIT license](http://choosealicense.com/licenses/mit/). You can use this class in both commercial and non-commercial projects provided that full header (minified and developer versions) is included. *© 2013-2014 Epistemex*