File: charts/js/CurveUtil.js

            /**
             * Provides functionality for drawing curves in a series.
             *
             * @module charts
             * @submodule series-curve-util
             */
            /**
             * Utility class used for calculating curve points.
             *
             * @class CurveUtil
             * @constructor
             * @submodule series-curve-util
             */
            function CurveUtil()
            {
            }
            
            CurveUtil.prototype = {
                /**
                 * Creates an array of start, end and control points for splines.
                 *
                 * @method getCurveControlPoints
                 * @param {Array} xcoords Collection of x-coordinates used for calculate the curves
                 * @param {Array} ycoords Collection of y-coordinates used for calculate the curves
                 * @return Object
                 * @protected
                 */
                getCurveControlPoints: function(xcoords, ycoords)
                {
            		var outpoints = [],
                        i = 1,
                        l = xcoords.length - 1,
                        xvals = [],
                        yvals = [];
            
            
            		// Too few points, need at least two
            		if (l < 1)
                    {
            			return null;
            		}
            
                    outpoints[0] = {
                        startx: xcoords[0],
                        starty: ycoords[0],
                        endx: xcoords[1],
                        endy: ycoords[1]
                    };
            
            		// Special case, the Bezier should be a straight line
                    if (l === 1)
                    {
            			outpoints[0].ctrlx1 = (2.0*xcoords[0] + xcoords[1])/3.0;
            			outpoints[0].ctrly2 = (2.0*ycoords[0] + ycoords[1])/3.0;
            			outpoints[0].ctrlx2 = 2.0*outpoints[0].ctrlx1 - xcoords[0];
                        outpoints[0].ctrly2 = 2.0*outpoints[0].ctrly1 - ycoords[0];
                        return outpoints;
            		}
            
            		for (; i < l; ++i)
                    {
            			outpoints.push({
                            startx: Math.round(xcoords[i]),
                            starty: Math.round(ycoords[i]),
                            endx: Math.round(xcoords[i+1]),
                            endy: Math.round(ycoords[i+1])
                        });
            			xvals[i] = 4.0 * xcoords[i] + 2*xcoords[i+1];
            			yvals[i] = 4.0*ycoords[i] + 2*ycoords[i+1];
            		}
            
            		xvals[0] = xcoords[0] + (2.0 * xcoords[1]);
            		xvals[l-1] = (8.0 * xcoords[l-1] + xcoords[l]) / 2.0;
            		xvals = this.getControlPoints(xvals.concat());
                    yvals[0] = ycoords[0] + (2.0 * ycoords[1]);
            		yvals[l-1] = (8.0 * ycoords[l-1] + ycoords[l]) / 2.0;
            		yvals = this.getControlPoints(yvals.concat());
            
                    for (i = 0; i < l; ++i)
                    {
            			outpoints[i].ctrlx1 = Math.round(xvals[i]);
                        outpoints[i].ctrly1 = Math.round(yvals[i]);
            
            			if (i < l-1)
                        {
            				outpoints[i].ctrlx2 = Math.round(2*xcoords[i+1] - xvals[i+1]);
                            outpoints[i].ctrly2 = Math.round(2*ycoords[i+1] - yvals[i+1]);
            			}
            			else
                        {
            				outpoints[i].ctrlx2 = Math.round((xcoords[l] + xvals[l-1])/2);
                            outpoints[i].ctrly2 = Math.round((ycoords[l] + yvals[l-1])/2);
            			}
            		}
            
            		return outpoints;
            	},
            
                /**
                 * Gets the control points for the curve.
                 *
                 * @method getControlPoints
                 * @param {Array} vals Collection of values coords used to generate control points.
                 * @return Array
                 * @private
                 */
            	getControlPoints: function(vals)
                {
            		var l = vals.length,
                        x = [],
                        tmp = [],
                        b = 2.0,
                        i = 1;
            		x[0] = vals[0] / b;
            		for (; i < l; ++i)
                    {
            			tmp[i] = 1/b;
            			b = (i < l-1 ? 4.0 : 3.5) - tmp[i];
            			x[i] = (vals[i] - x[i-1]) / b;
            		}
            
            		for (i = 1; i < l; ++i)
                    {
            			x[l-i-1] -= tmp[l-i] * x[l-i];
            		}
            
            		return x;
            	}
            };
            Y.CurveUtil = CurveUtil;