# Yahoo! UI Library

### widget-position-ext 3.0.0b1

Yahoo! UI Library > widget-position-ext > Widget-PositionExt.js (source view)
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    /**
     * Provides extended/advanced XY positioning support for Widgets, through an extension.
     *
     * It builds on top of the widget-position module, to provide alignmentment and centering support.
     * Future releases aim to add constrained and fixed positioning support.
     *
     * @module widget-position-ext
     */
            var L = Y.Lang,
                ALIGN = "align",

                BINDUI = "bindUI",
                SYNCUI = "syncUI",

                OFFSET_WIDTH = "offsetWidth",
                OFFSET_HEIGHT = "offsetHeight",
                VIEWPORT_REGION = "viewportRegion",
                REGION = "region",

                AlignChange = "alignChange";

            /**
             * Widget extension, which can be used to add extended XY positioning support to the base Widget class,
             * through the <a href="Base.html#method_build">Base.build</a> method. This extension requires that
             * the WidgetPosition extension be added to the Widget (before WidgetPositionExt, if part of the same
             * extension list passed to Base.build).
             *
             * @class WidgetPositionExt
             * @param {Object} User configuration object
             */
            function PositionExt(config) {
                if (!this.hasImpl(Y.WidgetPosition) || !this._posNode) {
                    Y.error("WidgetPosition needs to be added to the Widget, before WidgetPositionExt is added");
                }
                Y.after(this._syncUIPosExtras, this, SYNCUI);
                Y.after(this._bindUIPosExtras, this, BINDUI);
            }

            /**
             * Static property used to define the default attribute
             * configuration introduced by WidgetPositionExt.
             *
             * @property WidgetPositionExt.ATTRS
             * @type Object
             * @static
             */
            PositionExt.ATTRS = {

                /**
                 * @attribute align
                 * @type Object
                 * @default null
                 * @desciption The align attribute is used to align a reference point on the widget, with the refernce point on another node, or the viewport.
                 * The object which align expects has the following properties:
                 * <dl>
                 *       <dt>node</dt>
                 *       <dd>
                 *         The node to which the Widget is to be aligned. If set to null, or not provided, the Widget is aligned to the viewport
                 *       </dd>
                 *       <dt>points</dt>
                 *       <dd>
                 *         <p>
                 *         A two element array, defining the two points on the Widget and node/viewport which are to be aligned. The first element is the point on the Widget, and the second element is the point on the node/viewport.
                 *         Supported alignment points are defined as static properties on <code>WidgetPositionExt</code>.
                 *         </p>
                 *         <p>
                 *         e.g. <code>[WidgetPositionExt.TR, WidgetPositionExt.TL]</code> aligns the Top-Right corner of the Widget with the
                 *         Top-Left corner of the node/viewport, and <code>[WidgetPositionExt.CC, WidgetPositionExt.TC]</code> aligns the Center of the
                 *         Widget with the Top-Center edge of the node/viewport.
                 *         </p>
                 *       </dd>
                 *   </dl>
                 */
                align: {
                    value:null
                },

                /**
                 * @attribute centered
                 * @type {boolean | node}
                 * @default false
                 * @description A convenience attribute, which can be used as a shortcut for the align attribute.
                 * If set to true, the Widget is centered in the viewport. If set to a node reference or valid selector string,
                 * the Widget will be centered within the node. If set the false, no center positioning is applied.
                 */
                centered: {
                    setter: function(val) {
                        return this._setAlignCenter(val);
                    },
                    value:false
                }
            };

            /**
             * Constant used to specify the top-left corner for alignment
             *
             * @property WidgetPositionExt.TL
             * @type String
             * @static
             * @value "tl"
             */
            PositionExt.TL = "tl";
            /**
             * Constant used to specify the top-right corner for alignment
             *
             * @property WidgetPositionExt.TR
             * @type String
             * @static
             * @value "tr"
             */
            PositionExt.TR = "tr";
            /**
             * Constant used to specify the bottom-left corner for alignment
             *
             * @property WidgetPositionExt.BL
             * @type String
             * @static
             * @value "bl"
             */
            PositionExt.BL = "bl";
            /**
             * Constant used to specify the bottom-right corner for alignment
             *
             * @property WidgetPositionExt.BR
             * @type String
             * @static
             * @value "br"
             */
            PositionExt.BR = "br";
            /**
             * Constant used to specify the top edge-center point for alignment
             *
             * @property WidgetPositionExt.TC
             * @type String
             * @static
             * @value "tc"
             */
            PositionExt.TC = "tc";
            /**
             * Constant used to specify the right edge, center point for alignment
             *
             * @property WidgetPositionExt.RC
             * @type String
             * @static
             * @value "rc"
             */
            PositionExt.RC = "rc";
            /**
             * Constant used to specify the bottom edge, center point for alignment
             *
             * @property WidgetPositionExt.BC
             * @type String
             * @static
             * @value "bc"
             */
            PositionExt.BC = "bc";
            /**
             * Constant used to specify the left edge, center point for alignment
             *
             * @property WidgetPositionExt.LC
             * @type String
             * @static
             * @value "lc"
             */
            PositionExt.LC = "lc";
            /**
             * Constant used to specify the center of widget/node/viewport for alignment
             *
             * @property WidgetPositionExt.CC
             * @type String
             * @static
             * @value "cc"
             */
            PositionExt.CC = "cc";

            PositionExt.prototype = {

                /**
                 * Synchronizes the UI to match the Widgets extended positioning state.
                 * This method in invoked after syncUI is invoked for the Widget class
                 * using YUI's aop infrastructure.
                 *
                 * @method _syncUIPosExtras
                 * @protected
                 */
                _syncUIPosExtras : function() {
                    var align = this.get(ALIGN);
                    if (align) {
                        this._uiSetAlign(align.node, align.points);
                    }
                },

                /**
                 * Binds event listeners responsible for updating the UI state in response to
                 * Widget extended positioning related state changes.
                 * <p>
                 * This method is invoked after bindUI is invoked for the Widget class
                 * using YUI's aop infrastructure.
                 * </p>
                 * @method _bindUIStack
                 * @protected
                 */
                _bindUIPosExtras : function() {
                    this.after(AlignChange, this._afterAlignChange);
                },

                /**
                 * Default setter for center attribute changes. Sets up the appropriate value, and passes
                 * it through the to the align attribute.
                 *
                 * @method _setAlignCenter
                 * @protected
                 * @param {boolean | node} The attribute value being set.
                 * @return {Number} The attribute value being set.
                 */
                _setAlignCenter : function(val) {
                    if (val) {
                        this.set(ALIGN, {
                            node: val === true ? null : val,
                            points: [PositionExt.CC, PositionExt.CC]
                        });
                    }
                    return val;
                },

                /**
                 * Default attribute change listener for the align attribute, responsible
                 * for updating the UI, in response to attribute changes.
                 *
                 * @method _afterAlignChange
                 * @protected
                 * @param {EventFacade} e The event facade for the attribute change
                 */
                _afterAlignChange : function(e) {
                    if (e.newVal) {
                        this._uiSetAlign(e.newVal.node, e.newVal.points);
                    }
                },

                /**
                 * Updates the UI to reflect the align value passed in (see the align attribute documentation, for the object stucture expected)
                 * @method _uiSetAlign
                 * @protected
                 * @param {Node | null} The node to align to, or null to indicate the viewport
                 */
                _uiSetAlign: function (node, points) {

                    if (!L.isArray(points) || points.length != 2) {
                        Y.error("align: Invalid Points Arguments");
                        return;
                    }

                    var nodeRegion, widgetPoint, nodePoint, xy;

                    if (!node) {
                        nodeRegion = this._posNode.get(VIEWPORT_REGION);
                    } else {
                        node = Y.Node.get(node);
                        if (node) {
                            nodeRegion = node.get(REGION);
                        }
                    }

                    if (nodeRegion) {

                        // TODO: ViewportRegion doesn't have width/height - Workaround until normalized in Node/Dom
                        nodeRegion.width = nodeRegion.width || nodeRegion.right - nodeRegion.left;
                        nodeRegion.height = nodeRegion.height || nodeRegion.bottom - nodeRegion.top;

                        widgetPoint = points[0];
                        nodePoint = points[1];

                        // TODO: Optimize KWeight - Would lookup table help?
                        switch (nodePoint) {
                            case PositionExt.TL:
                                xy = [nodeRegion.left, nodeRegion.top];
                                break;
                            case PositionExt.TR:
                                xy = [nodeRegion.right, nodeRegion.top];
                                break;
                            case PositionExt.BL:
                                xy = [nodeRegion.left, nodeRegion.bottom];
                                break;
                            case PositionExt.BR:
                                xy = [nodeRegion.right, nodeRegion.bottom];
                                break;
                            case PositionExt.TC:
                                xy = [nodeRegion.left + Math.floor(nodeRegion.width/2), nodeRegion.top];
                                break;
                            case PositionExt.BC:
                                xy = [nodeRegion.left + Math.floor(nodeRegion.width/2), nodeRegion.bottom];
                                break;
                            case PositionExt.LC:
                                xy = [nodeRegion.left, nodeRegion.top + Math.floor(nodeRegion.height/2)];
                                break;
                            case PositionExt.RC:
                                xy = [nodeRegion.right, nodeRegion.top + Math.floor(nodeRegion.height/2), widgetPoint];
                                break;
                            case PositionExt.CC:
                                xy = [nodeRegion.left + Math.floor(nodeRegion.width/2), nodeRegion.top + Math.floor(nodeRegion.height/2), widgetPoint];
                                break;
                            default:
                                Y.log("align: Invalid Points Arguments", "info", "widget-position-extras");
                                break;
                        }

                        if (xy) {
                            this._doAlign(widgetPoint, xy[0], xy[1]);
                        }
                    }
                },

                /**
                 * Helper method, used to align the given point on the widget, with the XY page co-ordinates provided.
                 *
                 * @method _doAlign
                 * @private
                 * @param {String} widgetPoint Supported point constant (e.g. WidgetPositionExt.TL)
                 * @param {Number} x X page co-ordinate to align to
                 * @param {Number} y Y page co-ordinate to align to
                 */
                _doAlign : function(widgetPoint, x, y) {
                    var widgetNode = this._posNode,
                        xy;

                    switch (widgetPoint) {
                        case PositionExt.TL:
                            xy = [x, y];
                            break;
                        case PositionExt.TR:
                            xy = [x - widgetNode.get(OFFSET_WIDTH), y];
                            break;
                        case PositionExt.BL:
                            xy = [x, y - widgetNode.get(OFFSET_HEIGHT)];
                            break;
                        case PositionExt.BR:
                            xy = [x - widgetNode.get(OFFSET_WIDTH), y - widgetNode.get(OFFSET_HEIGHT)];
                            break;
                        case PositionExt.TC:
                            xy = [x - (widgetNode.get(OFFSET_WIDTH)/2), y];
                            break;
                        case PositionExt.BC:
                            xy = [x - (widgetNode.get(OFFSET_WIDTH)/2), y - widgetNode.get(OFFSET_HEIGHT)];
                            break;
                        case PositionExt.LC:
                            xy = [x, y - (widgetNode.get(OFFSET_HEIGHT)/2)];
                            break;
                        case PositionExt.RC:
                            xy = [(x - widgetNode.get(OFFSET_WIDTH)), y - (widgetNode.get(OFFSET_HEIGHT)/2)];
                            break;
                        case PositionExt.CC:
                            xy = [x - (widgetNode.get(OFFSET_WIDTH)/2), y - (widgetNode.get(OFFSET_HEIGHT)/2)];
                            break;
                        default:
                            Y.log("align: Invalid Points Argument", "info", "widget-position-extras");
                            break;
                    }

                    if (xy) {
                        this.move(xy);
                    }
                },

                /**
                 * Aligns the Widget to the provided node (or viewport) using the provided
                 * points. The method can be invoked directly, however it will result in
                 * the align attribute being out of sync with current position of the of Widget.
                 *
                 * @method align
                 * @param {Node | String | null} node A reference (or selector string) for the Node which with the Widget is to be aligned.
                 * If null is passed in, the Widget will be aligned with the viewport.
                 * @param {Array[2]} points A two element array, specifying the points on the Widget and node/viewport which need to be aligned.
                 * The first entry is the point on the Widget, and the second entry is the point on the node/viewport which need to align.
                 * Valid point references are defined as static constants on the WidgetPositionExt class.
                 *
                 * e.g. [WidgetPositionExt.TL, WidgetPositionExt.TR] will align the top-left corner of the Widget with the top-right corner of the node/viewport.
                 */
                align: function (node, points) {
                    this.set(ALIGN, {node: node, points:points});
                },

                /**
                 * Centers the container in the viewport, or if a node is passed in,
                 * the node.
                 *
                 * @method centered
                 * @param {Node | String} node Optional. A node reference or selector string defining the node
                 * inside which the Widget is to be centered. If not passed in, the Widget will be centered in the
                 * viewport.
                 */
                centered: function (node) {
                    this.align(node, [PositionExt.CC, PositionExt.CC]);
                }
            };

            Y.WidgetPositionExt = PositionExt;

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