phaser/src/geom/polygon/Smooth.js

A fast, free and fun HTML5 Game Framework for Desktop and Mobile web browsers from the team at Phaser Studio Inc.

/**
 * @author       Richard Davey <rich@phaser.io>
 * @author       Igor Ognichenko <ognichenko.igor@gmail.com>
 * @copyright    2013-2026 Phaser Studio Inc.
 * @license      {@link https://opensource.org/licenses/MIT|MIT License}
 */

/**
 * @ignore
 */
var copy = function (out, a)
{
    out[0] = a[0];
    out[1] = a[1];

    return out;
};

/**
 * Takes a Polygon object and applies Chaikin's smoothing algorithm on its points.
 *
 * Chaikin's algorithm is a corner-cutting technique that replaces each edge between
 * two consecutive points with two new points positioned along that edge, resulting in
 * a smoother curve. Each iteration of the algorithm increases the total number of points
 * in the polygon. The original first and last points are preserved, while all intermediate
 * points are replaced by pairs of new points at 85% and 15% along each edge.
 *
 * The polygon is modified in-place and the same polygon object is returned.
 *
 * @function Phaser.Geom.Polygon.Smooth
 * @since 3.13.0
 *
 * @generic {Phaser.Geom.Polygon} O - [polygon,$return]
 *
 * @param {Phaser.Geom.Polygon} polygon - The polygon to be smoothed. The polygon will be modified in-place and returned.
 *
 * @return {Phaser.Geom.Polygon} The input polygon.
 */
var Smooth = function (polygon)
{
    var i;
    var points = [];
    var data = polygon.points;

    for (i = 0; i < data.length; i++)
    {
        points.push([ data[i].x, data[i].y ]);
    }

    var output = [];

    if (points.length > 0)
    {
        output.push(copy([ 0, 0 ], points[0]));
    }

    for (i = 0; i < points.length - 1; i++)
    {
        var p0 = points[i];
        var p1 = points[i + 1];
        var p0x = p0[0];
        var p0y = p0[1];
        var p1x = p1[0];
        var p1y = p1[1];

        output.push([ 0.85 * p0x + 0.15 * p1x, 0.85 * p0y + 0.15 * p1y ]);
        output.push([ 0.15 * p0x + 0.85 * p1x, 0.15 * p0y + 0.85 * p1y ]);
    }

    if (points.length > 1)
    {
        output.push(copy([ 0, 0 ], points[points.length - 1]));
    }

    return polygon.setTo(output);
};

module.exports = Smooth;