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/* Copyright (c) 2006-2013 by OpenLayers Contributors (see authors.txt for
* full list of contributors). Published under the 2-clause BSD license.
* See license.txt in the OpenLayers distribution or repository for the
* full text of the license. */
/**
* @requires OpenLayers/Tile.js
* @requires OpenLayers/Format/JSON.js
* @requires OpenLayers/Request.js
*/
/**
* Class: OpenLayers.Tile.UTFGrid
* Instances of OpenLayers.Tile.UTFGrid are used to manage
* UTFGrids. This is an unusual tile type in that it doesn't have a
* rendered image; only a 'hit grid' that can be used to
* look up feature attributes.
*
* See the <OpenLayers.Tile.UTFGrid> constructor for details on constructing a
* new instance.
*
* Inherits from:
* - <OpenLayers.Tile>
*/
OpenLayers.Tile.UTFGrid = OpenLayers.Class(OpenLayers.Tile, {
/**
* Property: url
* {String}
* The URL of the UTFGrid file being requested. Provided by the <getURL>
* method.
*/
url: null,
/**
* Property: utfgridResolution
* {Number}
* Ratio of the pixel width to the width of a UTFGrid data point. If an
* entry in the grid represents a 4x4 block of pixels, the
* utfgridResolution would be 4. Default is 2.
*/
utfgridResolution: 2,
/**
* Property: json
* {Object}
* Stores the parsed JSON tile data structure.
*/
json: null,
/**
* Property: format
* {OpenLayers.Format.JSON}
* Parser instance used to parse JSON for cross browser support. The native
* JSON.parse method will be used where available (all except IE<8).
*/
format: null,
/**
* Constructor: OpenLayers.Tile.UTFGrid
* Constructor for a new <OpenLayers.Tile.UTFGrid> instance.
*
* Parameters:
* layer - {<OpenLayers.Layer>} layer that the tile will go in.
* position - {<OpenLayers.Pixel>}
* bounds - {<OpenLayers.Bounds>}
* url - {<String>} Deprecated. Remove me in 3.0.
* size - {<OpenLayers.Size>}
* options - {Object}
*/
/**
* APIMethod: destroy
* Clean up.
*/
destroy: function() {
this.clear();
OpenLayers.Tile.prototype.destroy.apply(this, arguments);
},
/**
* Method: draw
* Check that a tile should be drawn, and draw it.
* In the case of UTFGrids, "drawing" it means fetching and
* parsing the json.
*
* Returns:
* {Boolean} Was a tile drawn?
*/
draw: function() {
var drawn = OpenLayers.Tile.prototype.draw.apply(this, arguments);
if (drawn) {
if (this.isLoading) {
this.abortLoading();
//if we're already loading, send 'reload' instead of 'loadstart'.
this.events.triggerEvent("reload");
} else {
this.isLoading = true;
this.events.triggerEvent("loadstart");
}
this.url = this.layer.getURL(this.bounds);
if (this.layer.useJSONP) {
// Use JSONP method to avoid xbrowser policy
var ols = new OpenLayers.Protocol.Script({
url: this.url,
callback: function(response) {
this.isLoading = false;
this.events.triggerEvent("loadend");
this.json = response.data;
},
scope: this
});
ols.read();
this.request = ols;
} else {
// Use standard XHR
this.request = OpenLayers.Request.GET({
url: this.url,
callback: function(response) {
this.isLoading = false;
this.events.triggerEvent("loadend");
if (response.status === 200) {
this.parseData(response.responseText);
}
},
scope: this
});
}
} else {
this.unload();
}
return drawn;
},
/**
* Method: abortLoading
* Cancel a pending request.
*/
abortLoading: function() {
if (this.request) {
this.request.abort();
delete this.request;
}
this.isLoading = false;
},
/**
* Method: getFeatureInfo
* Get feature information associated with a pixel offset. If the pixel
* offset corresponds to a feature, the returned object will have id
* and data properties. Otherwise, null will be returned.
*
*
* Parameters:
* i - {Number} X-axis pixel offset (from top left of tile)
* j - {Number} Y-axis pixel offset (from top left of tile)
*
* Returns:
* {Object} Object with feature id and data properties corresponding to the
* given pixel offset.
*/
getFeatureInfo: function(i, j) {
var info = null;
if (this.json) {
var id = this.getFeatureId(i, j);
if (id !== null) {
info = {id: id, data: this.json.data[id]};
}
}
return info;
},
/**
* Method: getFeatureId
* Get the identifier for the feature associated with a pixel offset.
*
* Parameters:
* i - {Number} X-axis pixel offset (from top left of tile)
* j - {Number} Y-axis pixel offset (from top left of tile)
*
* Returns:
* {Object} The feature identifier corresponding to the given pixel offset.
* Returns null if pixel doesn't correspond to a feature.
*/
getFeatureId: function(i, j) {
var id = null;
if (this.json) {
var resolution = this.utfgridResolution;
var row = Math.floor(j / resolution);
var col = Math.floor(i / resolution);
var charCode = this.json.grid[row].charCodeAt(col);
var index = this.indexFromCharCode(charCode);
var keys = this.json.keys;
if (!isNaN(index) && (index in keys)) {
id = keys[index];
}
}
return id;
},
/**
* Method: indexFromCharCode
* Given a character code for one of the UTFGrid "grid" characters,
* resolve the integer index for the feature id in the UTFGrid "keys"
* array.
*
* Parameters:
* charCode - {Integer}
*
* Returns:
* {Integer} Index for the feature id from the keys array.
*/
indexFromCharCode: function(charCode) {
if (charCode >= 93) {
charCode--;
}
if (charCode >= 35) {
charCode --;
}
return charCode - 32;
},
/**
* Method: parseData
* Parse the JSON from a request
*
* Parameters:
* str - {String} UTFGrid as a JSON string.
*
* Returns:
* {Object} parsed javascript data
*/
parseData: function(str) {
if (!this.format) {
this.format = new OpenLayers.Format.JSON();
}
this.json = this.format.read(str);
},
/**
* Method: clear
* Delete data stored with this tile.
*/
clear: function() {
this.json = null;
},
CLASS_NAME: "OpenLayers.Tile.UTFGrid"
});