phaser/src/physics/matter-js/lib/geometry/Axes.js

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/**
* The `Matter.Axes` module contains methods for creating and manipulating sets of axes.
*
* @class Axes
*/

var Axes = {};

module.exports = Axes;

var Vector = require('../geometry/Vector');
var Common = require('../core/Common');

(function() {

    /**
     * Creates a new set of axes from the given vertices.
     * @method fromVertices
     * @param {vertices} vertices
     * @return {axes} A new axes from the given vertices
     */
    Axes.fromVertices = function(vertices) {
        var axes = {};

        // find the unique axes, using edge normal gradients
        for (var i = 0; i < vertices.length; i++) {
            var j = (i + 1) % vertices.length, 
                normal = Vector.normalise({ 
                    x: vertices[j].y - vertices[i].y, 
                    y: vertices[i].x - vertices[j].x
                }),
                gradient = (normal.y === 0) ? Infinity : (normal.x / normal.y);
            
            // limit precision
            gradient = gradient.toFixed(3).toString();
            axes[gradient] = normal;
        }

        return Common.values(axes);
    };

    /**
     * Rotates a set of axes by the given angle.
     * @method rotate
     * @param {axes} axes
     * @param {number} angle
     */
    Axes.rotate = function(axes, angle) {
        if (angle === 0)
            return;
        
        var cos = Math.cos(angle),
            sin = Math.sin(angle);

        for (var i = 0; i < axes.length; i++) {
            var axis = axes[i],
                xx;
            xx = axis.x * cos - axis.y * sin;
            axis.y = axis.x * sin + axis.y * cos;
            axis.x = xx;
        }
    };

})();