/**

* 一直覆盖在当前地图视野的覆盖物

*

* @author nikai (@胖嘟嘟的骨头, nikai@baidu.com)

*

* @param

* {

* map 地图实例对象

* elementTag 覆盖物容器的标签类型，默认是div，我们这canvas用的多

* }

*/

function MapMask(options){

this.options = options || {};

this.initElement();

this._map = options.map;

this.show();

}

MapMask.prototype = new BMap.Overlay();

MapMask.prototype.initialize = function(map){

this._map = map;

var elementTag = this.options.elementTag || "div";

var element = this.element = document.createElement(elementTag);

var size = map.getSize();

element.width = size.width;

element.height = size.height;

element.style.cssText = "position:absolute;"

+ "left:0;"

+ "top:0;"

+ "width:" + size.width + "px;"

+ "height:" + size.height + "px";

if (this.options.zIndex !== undefined) {

element.style.zIndex = this.options.zIndex;

}

map.getPanes().labelPane.appendChild(this.element);

return this.element;

}

MapMask.prototype.initElement = function(map){

}

MapMask.prototype.draw = function(){

var map = this._map;

var bounds = map.getBounds();

var sw = bounds.getSouthWest();

var ne = bounds.getNorthEast();

var pixel = map.pointToOverlayPixel(new BMap.Point(sw.lng, ne.lat));

this.element.style.left = pixel.x + "px";

this.element.style.top = pixel.y + "px";

this.dispatchEvent('draw');

}

MapMask.prototype.getContainer = function(){

return this.element;

}

MapMask.prototype.show = function(){

this._map.addOverlay(this);

}

MapMask.prototype.hide = function(){

this._map.removeOverlay(this);

}