openlayers/lib/OpenLayers/Tile.js

/* Copyright (c) 2006 MetaCarta, Inc., published under a modified BSD license.
 * See http://svn.openlayers.org/trunk/openlayers/repository-license.txt 
 * for the full text of the license. */


/*
 * @class 
 * @requires OpenLayers/Util.js
 * 
 * This is a class designed to designate a single tile, however
 * it is explicitly designed to do relatively little. Tiles store information
 * about themselves -- such as the URL that they are related to, and their 
 * size - but do not add themselves to the layer div automatically, for 
 * example.
 * 
 * TBD 3.0 - remove reference to url in above paragraph
 * 
 */
OpenLayers.Tile = OpenLayers.Class.create();
OpenLayers.Tile.prototype = {
    
    /** @type String */
    id: null,
    
    /** @type OpenLayers.Layer */
    layer: null,
    
    /** TBD 3.0 
     * @deprecated The base tile class does not need an url. This should be 
     *              handled in subclasses. Does not belong here.
     * 
     * @type String url of the request */
    url:null,

    /** @type OpenLayers.Bounds */
    bounds:null,
    
    /** @type OpenLayers.Size */
    size:null,
    
    /** Top Left pixel of the tile
    * @type OpenLayers.Pixel */
    position:null,

    /** @type Boolean */
    drawn: false,

    /** TBD 3.0 -- remove 'url' from the list of parameters to the constructor.
     *             there is no need for the base tile class to have a url.
     * 
    * @constructor
    *
    * @param {OpenLayers.Layer} layer
    * @param {OpenLayers.Pixel} position
    * @param {OpenLayers.Bounds} bounds
    * @param {String} url
    * @param {OpenLayers.Size} size
    */   
    initialize: function(layer, position, bounds, url, size) {
        this.layer = layer;
        this.position = position;
        this.bounds = bounds;
        this.url = url;
        this.size = size;

        //give the tile a unique id based on its BBOX.
        this.id = OpenLayers.Util.createUniqueID("Tile_");
    },
    
    /** nullify references to prevent circular references and memory leaks
    */
    destroy:function() {
        this.layer  = null;
        this.bounds = null;
        this.size = null;
        this.position = null;
    },

    /**
    */
    draw:function() {
        this.clear();
        return ((this.layer.displayOutsideMaxExtent
                || (this.layer.maxExtent
                    && this.bounds.intersectsBounds(this.layer.maxExtent, false)))
                && !(this.layer.buffer == 0
                     && !this.bounds.intersectsBounds(this.layer.map.getExtent(), false)));
    },
    
    /** 
     * @param {OpenLayers.Bounds}
     * @param {OpenLayers.pixel} position
     * @param {Boolean} redraw Redraw tile after moving? 
     *                         Default is true
     */
    moveTo: function (bounds, position, redraw) {
        if (redraw == null) {
            redraw = true;
        }

        this.clear();
        this.bounds = bounds.clone();
        this.position = position.clone();
        if (redraw) {
            this.draw();
        }
    },

    /** Clear the tile of any bounds/position-related data so that it can 
     *   be reused in a new location.
     */
    clear: function() {
        this.drawn = false;
    },
    
    getBoundsFromBaseLayer: function(position) {
        var topLeft = this.layer.map.getLonLatFromLayerPx(position); 
        var bottomRightPx = position.clone();
        bottomRightPx.x += this.size.w;
        bottomRightPx.y += this.size.h;
        var bottomRight = this.layer.map.getLonLatFromLayerPx(bottomRightPx); 
        // Handle the case where the base layer wraps around the date line.
        // Google does this, and it breaks WMS servers to request bounds in that fashion.  
        if (topLeft.lon > bottomRight.lon) {
            if (topLeft.lon < 0) {
                topLeft.lon = -180 - (topLeft.lon+180);
            } else {
                bottomRight.lon = 180+bottomRight.lon+180;
            }        
        }
        bounds = new OpenLayers.Bounds(topLeft.lon, bottomRight.lat, bottomRight.lon, topLeft.lat);  
        return bounds;
    },        

    /** @final @type String */
    CLASS_NAME: "OpenLayers.Tile"
};