i took a look at the minified source code and it looks like we are wiring up a mouseMove event handler specific to polygons. once the number of input points is greater than two, an additional path is added to the graphic geometry (connecting back to the first vertex).
_measureAreaMouseMoveHandler : function (evt) {
var _36;
//after the first vertex is created...
if (this.inputPoints.length > 0) {
var _37 = new _15(this._map.spatialReference);
var _38;
//snap if snapping is enabled
if (this._map.snappingManager) {
_38 = this._map.snappingManager._snappingPoint;
}
_36 = _38 || evt.mapPoint;
//add a path between the first vertex and where the mouse is hovering
_37.addPath([this._currentStartPt, _36]);
var _39 = this._densifyGeometry(_37);
//add the geometry to the graphic
this.tempGraphic.setGeometry(_39);
}
//after two verticies have been created...
if (this.inputPoints.length > 1) {
var _3a = new _15(this._map.spatialReference);
//add a path back to the first point
_3a.addPath([_36, this.inputPoints[0]]);
var _3b = this._densifyGeometry(_3a);
//add the geometry to the graphic
this.tempGraphic.setGeometry(this.tempGraphic.geometry.addPath(_3b.paths[0]));
}
},
since the draw toolbar itself doesn't already have an eventHandler to hook up to, you'd have to create your own. to be perfectly honest, i have no idea how you could get a reference to the same kind of "temporary" graphic.
