# Yahoo! UI Library

### dd 3.1.1

Yahoo! UI Library > dd > ddm.js (source view)
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        /**
         * Extends the dd-ddm-base Class to add support for the viewport shim to allow a draggable node to drag to be dragged over an iframe or any other node that traps mousemove events.
         * It is also required to have Drop Targets enabled, as the viewport shim will contain the shims for the Drop Targets.
         * @module dd
         * @submodule dd-ddm
         * @for DDM
         * @namespace DD
         */
        Y.mix(Y.DD.DDM, {
            /**
            * @private
            * @property _pg
            * @description The shim placed over the screen to track the mousemove event.
            * @type {Node}
            */
            _pg: null,
            /**
            * @private
            * @property _debugShim
            * @description Set this to true to set the shims opacity to .5 for debugging it, default: false.
            * @type {Boolean}
            */
            _debugShim: false,
            _activateTargets: function() { },
            _deactivateTargets: function() {},
            _startDrag: function() {
                if (this.activeDrag.get('useShim')) {
                    this._pg_activate();
                    this._activateTargets();
                }
            },
            _endDrag: function() {
                this._pg_deactivate();
                this._deactivateTargets();
            },
            /**
            * @private
            * @method _pg_deactivate
            * @description Deactivates the shim
            */
            _pg_deactivate: function() {
                this._pg.setStyle('display', 'none');
            },
            /**
            * @private
            * @method _pg_activate
            * @description Activates the shim
            */
            _pg_activate: function() {
                var ah = this.activeDrag.get('activeHandle'), cur = 'auto';
                if (ah) {
                    cur = ah.getStyle('cursor');
                }
                if (cur == 'auto') {
                    cur = this.get('dragCursor');
                }

                this._pg_size();
                this._pg.setStyles({
                    top: 0,
                    left: 0,
                    display: 'block',
                    opacity: ((this._debugShim) ? '.5' : '0'),
                    cursor: cur
                });
            },
            /**
            * @private
            * @method _pg_size
            * @description Sizes the shim on: activatation, window:scroll, window:resize
            */
            _pg_size: function() {
                if (this.activeDrag) {
                    var b = Y.one('body'),
                    h = b.get('docHeight'),
                    w = b.get('docWidth');
                    this._pg.setStyles({
                        height: h + 'px',
                        width: w + 'px'
                    });
                }
            },
            /**
            * @private
            * @method _createPG
            * @description Creates the shim and adds it's listeners to it.
            */
            _createPG: function() {
                var pg = Y.Node.create('<div></div>'),
                bd = Y.one('body'), win;
                pg.setStyles({
                    top: '0',
                    left: '0',
                    position: 'absolute',
                    zIndex: '9999',
                    overflow: 'hidden',
                    backgroundColor: 'red',
                    display: 'none',
                    height: '5px',
                    width: '5px'
                });
                pg.set('id', Y.stamp(pg));
                pg.addClass('yui3-dd-shim');
                if (bd.get('firstChild')) {
                    bd.insertBefore(pg, bd.get('firstChild'));
                } else {
                    bd.appendChild(pg);
                }
                this._pg = pg;
                this._pg.on('mouseup', Y.bind(this._end, this));
                this._pg.on('mousemove', Y.throttle(Y.bind(this._move, this), this.get('throttleTime')));

                win = Y.one(window);
                Y.on('window:resize', Y.bind(this._pg_size, this));
                win.on('scroll', Y.bind(this._pg_size, this));
            }
        }, true);

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