function sortChildren(a, b) {
    if (a.zIndex === b.zIndex) {
        return a._lastSortedIndex - b._lastSortedIndex;
    }
    return a.zIndex - b.zIndex;
}
Constants for various buffer types in Pixi
@see PIXI.BUFFER_TYPE
@name BUFFER_TYPE
@memberof PIXI
@static
@enum {number}
@property {number} ELEMENT_ARRAY_BUFFER - buffer type for using as an index buffer
@property {number} ARRAY_BUFFER - buffer type for using attribute data
@property {number} UNIFORM_BUFFER - the buffer type is for uniform buffer objects