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. */


/*
 * @requires OpenLayers/Util.js
 *
 * Class: OpenLayers.Tile 
 * 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. Create a new tile with the <OpenLayers.Tile> constructor, or 
 * a subclass. 
 * 
 * TBD 3.0 - remove reference to url in above paragraph
 * 
 */
OpenLayers.Tile = OpenLayers.Class.create();
OpenLayers.Tile.prototype = {
    
    /** 
	 * Property: id 
	 * {String} null
	 */
	id: null,
    
    /** 
	 * Property: layer 
	 * {<OpenLayers.Layer>} layer the tile is attached to 
	 */
	layer: null,
    
    /**
     * Property: url
     * {String} url of the request 
     *
     * TBD 3.0 
     * Deprecated. The base tile class does not need an url. This should be 
     * handled in subclasses. Does not belong here.
     */
    url: null,

    /** 
	 * APIProperty: bounds 
	 * {<OpenLayers.Bounds>} null
	 */
	bounds: null,
    
    /** 
	 * Property: size 
	 * {<OpenLayers.Size>} null
	 */
	size: null,
    
    /** 
	 * Property: position 
	 * {<OpenLayers.Pixel>} Top Left pixel of the tile
	 */	
    position: null,

    /** 
	 * Property: drawn 
	 * {Boolean} false
	 */
	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: OpenLayers.Tile
     * Constructor for a new <OpenLayers.Tile> instance.
     * 
     * Parameters:
     * layer - {<OpenLayers.Layer>} layer that the tile will go in.
     * position - {<OpenLayers.Pixel>}
     * bounds - {<OpenLayers.Bounds>}
     * url - {<String>}
     * size - {<OpenLayers.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_");
    },
    
    /** 
     * APIMethod: destroy
     * nullify references to prevent circular references and memory leaks
     */
    destroy:function() {
        this.layer  = null;
        this.bounds = null;
        this.size = null;
        this.position = null;
    },

    /**
     * Method: draw
     * Clear whatever is currently in the tile, then return whether or not 
     *  it should actually be re-drawn.
     * 
     * Return:
     * {Boolean} Whether or not the tile should actually be drawn. Note that 
     *           this is not really the best way of doing things, but such is 
     *           the way the code has been developed. Subclasses call this and
     *           depend on the return to know if they should draw or not.
     */
    draw: function() {
        
        //clear tile's contents and mark as not drawn
        this.clear();
        
        var maxExtent = this.layer.maxExtent;
        var withinMaxExtent = (maxExtent &&
                               this.bounds.intersectsBounds(maxExtent, false));
 
        var mapExtent = this.layer.map.getExtent();
        var withinMapExtent = (mapExtent &&
                               this.bounds.intersectsBounds(mapExtent, false));
         
        // There are two cases where we *wouldn't* want to draw the tile:
        //  
        // 1) If the tile is outside its layer's maxExtent
        // 2) When the layer's buffer is 0, if the tile is outside the map's 
        //    extent (out of view)
        //
        // ...what we return is the opposite of the above conditions :-)
        //
        return ( (withinMaxExtent || this.layer.displayOutsideMaxExtent) &&
                 (withinMapExtent || (this.layer.buffer != 0)) );
    },
    
    /** 
     * Method: moveTo
     * Reposition the tile.
     *
     * Parameters:
     * bounds - {<OpenLayers.Bounds>}
     * position - {<OpenLayers.Pixel>}
     * redraw - {Boolean} Call draw method on 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();
        }
    },

    /** 
     * Method: clear
     * Clear the tile of any bounds/position-related data so that it can 
     * be reused in a new location.
     */
    clear: function() {
        this.drawn = false;
    },
    
    /**   
     * Method: getBoundsFromBaseLayer
     * Take the pixel locations of the corner of the tile, and pass them to the base layer 
     * and ask for the location of those pixels, so that displaying tiles over Google
     * works fine.
     *
     * Parameters:
     * position - {<OpenLayers.Pixel>}
     *
     * Return:
     * bounds - {<OpenLayers.Bounds>} 
     */
    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"
};