OpenLayers源码学习17:图层Layer.HTTPRequest

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本来想直接看wmts这个协议的实现, 结果发现Layer.WMTS继承于Layer.Grid 继承于Layer.HTTPRequest
东西太多 所以还是按顺序看比较好…

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OpenLayers.Layer.HTTPRequest = OpenLayers.Class(OpenLayers.Layer, {
 
    //哈希因子, 注释说是应对多个wms用的 全代码只有一个
    URL_HASH_FACTOR: (Math.sqrt(5) - 1) / 2,
 
    // 可能string或者数组
    url: null,
 
    //哈希的 k/v 
    params: null,
     
    // 是否将此图层按base layer转换投影, 默认false
    reproject: false,
 
    //构造, 继承于OpenLayers.Layer. 参数名字挺好不用再解释了...
    initialize: function(name, url, params, options) {
        //调用父对象的initialize, 传新参数构造
        OpenLayers.Layer.prototype.initialize.apply(this, [name, options]);
        //处理子类配置
        this.url = url;
        if (!this.params) {
            this.params = OpenLayers.Util.extend({}, params);
        }
    },
 
    //销毁
    destroy: function() {
        //先处理构造时后添加的
        this.url = null;
        this.params = null;
        //再调用父类的析构
        OpenLayers.Layer.prototype.destroy.apply(this, arguments); 
    },
     
    //克隆 
    clone: function (obj) {
         
        if (obj == null) {
            obj = new OpenLayers.Layer.HTTPRequest(this.name,
                                                   this.url,
                                                   this.params,
                                                   this.getOptions());
        }
         
        //创建一个新的之后, 
        obj = OpenLayers.Layer.prototype.clone.apply(this, [obj]);
         
        return obj;
    },
 
    setUrl: function(newUrl) {
        this.url = newUrl;
    },
 
    // 合并新参数, 触发图层重绘
    mergeNewParams:function(newParams) {
        this.params = OpenLayers.Util.extend(this.params, newParams);
        var ret = this.redraw();
        if(this.map != null) {
            this.map.events.triggerEvent("changelayer", {
                layer: this,
                property: "params"
            });
        }
        return ret;
    },
 
    //重绘图层, 强制重绘会mergeNewParams
    redraw: function(force) { 
        if (force) {
            return this.mergeNewParams({"_olSalt": Math.random()});
        } else {
            return OpenLayers.Layer.prototype.redraw.apply(this, []);
        }
    },
     
    //选择url, 
    //没太看懂, 应该是个哈希算法, 最终取到指定的url[idx]
    selectUrl: function(paramString, urls) {
        var product = 1;
        for (var i=0, len=paramString.length; i<len; i++) { 
            product *= paramString.charCodeAt(i) * this.URL_HASH_FACTOR; 
            product -= Math.floor(product); 
        }
        return urls[Math.floor(product * urls.length)];
    },
 
    // 最终返回url形如: server?key1=value1&key2=value2&key3=value3
    getFullRequestString:function(newParams, altUrl) {
        // 如果没有altUrl就用本图层的url
        var url = altUrl || this.url;
         
        // 克隆this.params, 合并传参中的newParams, 剥离k/v
        var allParams = OpenLayers.Util.extend({}, this.params);
        allParams = OpenLayers.Util.extend(allParams, newParams);
        var paramsString = OpenLayers.Util.getParameterString(allParams);
         
        // 如果url是数组, 利用哈希剥离
        if (OpenLayers.Util.isArray(url)) {
            url = this.selectUrl(paramsString, url);
        }   
  
        // 忽略大小写
        var urlParams = 
            OpenLayers.Util.upperCaseObject(OpenLayers.Util.getParameters(url));
        for(var key in allParams) {
            if(key.toUpperCase() in urlParams) {
                delete allParams[key];
            }
        }
        paramsString = OpenLayers.Util.getParameterString(allParams);
         
        return OpenLayers.Util.urlAppend(url, paramsString);
    },
 
    CLASS_NAME: "OpenLayers.Layer.HTTPRequest"
});