konva/src/filters/Posterize.js

(function () {

    /**
     * Posterize Filter. Adjusts the channels so that there are no more
     *  than n different values for that channel. This is also applied
     *  to the alpha channel.
     * @function
     * @name Posterize
     * @author ippo615
     * @memberof Kinetic.Filters
     * @param {Object} imageData
     * @example
     * node.cache();
     * node.filters([Kinetic.Filters.Posterize]);
     * node.levels(0.8);
     */

    Kinetic.Filters.Posterize = function (imageData) {
        // level must be between 1 and 255
        var levels = Math.round(this.levels() * 254) + 1,
            data = imageData.data,
            len = data.length,
            scale = (255 / levels),
            i;

        for (i = 0; i < len; i += 1) {
            data[i] = Math.floor(data[i] / scale) * scale;
        }
    };

    Kinetic.Factory.addGetterSetter(Kinetic.Node, 'levels', 0.5, null, Kinetic.Factory.afterSetFilter);

    /**
    * get/set levels.  Must be a number between 0 and 1.  Use with {@link Kinetic.Filters.Posterize} filter.
    * @name levels
    * @method
    * @memberof Kinetic.Node.prototype
    * @param {Number} level between 0 and 1
    * @returns {Number}
    */
})();