charts/js/CurveUtil.js

	CurveUtil.js revision cec703a844d9691646231634fe709f4ea41d278a
/**
 * Utility class used for calculating curve points.
 *
 * @class CurveUtil
 * @constructor
 */
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;