Source: src/gameobjects/components/ScaleMinMax.js

/**
* @author       Richard Davey <rich@photonstorm.com>
* @copyright    2016 Photon Storm Ltd.
* @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
*/

/**
* The ScaleMinMax component allows a Game Object to limit how far it can be scaled by its parent.
*
* @class
*/
Phaser.Component.ScaleMinMax = function () {};

Phaser.Component.ScaleMinMax.prototype = {

    /**
    * The callback that will apply any scale limiting to the worldTransform.
    * @property {function} transformCallback
    */
    transformCallback: null,

    /**
    * The context under which `transformCallback` is called.
    * @property {object} transformCallbackContext
    */
    transformCallbackContext: this,

    /**
    * The minimum scale this Game Object will scale down to.
    *
    * It allows you to prevent a parent from scaling this Game Object lower than the given value.
    *
    * Set it to `null` to remove the limit.
    * @property {Phaser.Point} scaleMin
    */
    scaleMin: null,

    /**
    * The maximum scale this Game Object will scale up to.
    *
    * It allows you to prevent a parent from scaling this Game Object higher than the given value.
    *
    * Set it to `null` to remove the limit.
    * @property {Phaser.Point} scaleMax
    */
    scaleMax: null,

    /**
     * Adjust scaling limits, if set, to this Game Object.
     *
     * @method
     * @private
     * @param {Phaser.Matrix} wt - The updated worldTransform matrix.
     */
    checkTransform: function (wt) {

        if (this.scaleMin)
        {
            if (wt.a < this.scaleMin.x)            {
                wt.a = this.scaleMin.x;
            }

            if (wt.d < this.scaleMin.y)            {
                wt.d = this.scaleMin.y;
            }
        }

        if (this.scaleMax)
        {
            if (wt.a > this.scaleMax.x)
            {
                wt.a = this.scaleMax.x;
            }

            if (wt.d > this.scaleMax.y)
            {
                wt.d = this.scaleMax.y;
            }
        }

    },

    /**
     * Sets the scaleMin and scaleMax values. These values are used to limit how far this Game Object will scale based on its parent.
     *
     * For example if this Game Object has a `minScale` value of 1 and its parent has a `scale` value of 0.5, the 0.5 will be ignored
     * and the scale value of 1 will be used, as the parents scale is lower than the minimum scale this Game Object should adhere to.
     *
     * By setting these values you can carefully control how Game Objects deal with responsive scaling.
     *
     * If only one parameter is given then that value will be used for both scaleMin and scaleMax:
     * `setScaleMinMax(1)` = scaleMin.x, scaleMin.y, scaleMax.x and scaleMax.y all = 1
     *
     * If only two parameters are given the first is set as scaleMin.x and y and the second as scaleMax.x and y:
     * `setScaleMinMax(0.5, 2)` = scaleMin.x and y = 0.5 and scaleMax.x and y = 2
     *
     * If you wish to set `scaleMin` with different values for x and y then either modify Game Object.scaleMin directly,
     * or pass `null` for the `maxX` and `maxY` parameters.
     *
     * Call `setScaleMinMax(null)` to clear all previously set values.
     *
     * @method
     * @param {number|null} minX - The minimum horizontal scale value this Game Object can scale down to.
     * @param {number|null} minY - The minimum vertical scale value this Game Object can scale down to.
     * @param {number|null} maxX - The maximum horizontal scale value this Game Object can scale up to.
     * @param {number|null} maxY - The maximum vertical scale value this Game Object can scale up to.
     */
    setScaleMinMax: function (minX, minY, maxX, maxY) {

        if (minY === undefined)
        {
            //  1 parameter, set all to it
            minY = maxX = maxY = minX;
        }
        else if (maxX === undefined)
        {
            //  2 parameters, the first is min, the second max
            maxX = maxY = minY;
            minY = minX;
        }

        if (minX === null)
        {
            this.scaleMin = null;
        }
        else
        {
            if (this.scaleMin)
            {
                this.scaleMin.set(minX, minY);
            }
            else
            {
                this.scaleMin = new Phaser.Point(minX, minY);
            }
        }

        if (maxX === null)
        {
            this.scaleMax = null;
        }
        else
        {
            if (this.scaleMax)
            {
                this.scaleMax.set(maxX, maxY);
            }
            else
            {
                this.scaleMax = new Phaser.Point(maxX, maxY);
            }
        }

        if (this.scaleMin === null)
        {
            this.transformCallback = null;
        }
        else
        {
            this.transformCallback = this.checkTransform;
            this.transformCallbackContext = this;
        }

    }

};