path: root/misc/openlayers/lib/OpenLayers/Tile/Image.js

/* 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/Animation.js
 * @requires OpenLayers/Util.js
 */

/**
 * Class: OpenLayers.Tile.Image
 * Instances of OpenLayers.Tile.Image are used to manage the image tiles
 * used by various layers.  Create a new image tile with the
 * <OpenLayers.Tile.Image> constructor.
 *
 * Inherits from:
 *  - <OpenLayers.Tile>
 */
OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {

    /**
     * APIProperty: events
     * {<OpenLayers.Events>} An events object that handles all 
     *     events on the tile.
     *
     * Register a listener for a particular event with the following syntax:
     * (code)
     * tile.events.register(type, obj, listener);
     * (end)
     *
     * Supported event types (in addition to the <OpenLayers.Tile> events):
     * beforeload - Triggered before an image is prepared for loading, when the
     *     url for the image is known already. Listeners may call <setImage> on
     *     the tile instance. If they do so, that image will be used and no new
     *     one will be created.
     */

    /** 
     * APIProperty: url
     * {String} The URL of the image being requested. No default. Filled in by
     * layer.getURL() function. May be modified by loadstart listeners.
     */
    url: null,
    
    /** 
     * Property: imgDiv
     * {HTMLImageElement} The image for this tile.
     */
    imgDiv: null,
    
    /**
     * Property: frame
     * {DOMElement} The image element is appended to the frame.  Any gutter on
     * the image will be hidden behind the frame. If no gutter is set,
     * this will be null.
     */ 
    frame: null, 

    /** 
     * Property: imageReloadAttempts
     * {Integer} Attempts to load the image.
     */
    imageReloadAttempts: null,
    
    /**
     * Property: layerAlphaHack
     * {Boolean} True if the png alpha hack needs to be applied on the layer's div.
     */
    layerAlphaHack: null,
    
    /**
     * Property: asyncRequestId
     * {Integer} ID of an request to see if request is still valid. This is a
     * number which increments by 1 for each asynchronous request.
     */
    asyncRequestId: null,
    
    /**
     * APIProperty: maxGetUrlLength
     * {Number} If set, requests that would result in GET urls with more
     * characters than the number provided will be made using form-encoded
     * HTTP POST. It is good practice to avoid urls that are longer than 2048
     * characters.
     *
     * Caution:
     * Older versions of Gecko based browsers (e.g. Firefox < 3.5) and most
     * Opera versions do not fully support this option. On all browsers,
     * transition effects are not supported if POST requests are used.
     */
    maxGetUrlLength: null,

    /**
     * Property: canvasContext
     * {CanvasRenderingContext2D} A canvas context associated with
     * the tile image.
     */
    canvasContext: null,
    
    /**
     * APIProperty: crossOriginKeyword
     * The value of the crossorigin keyword to use when loading images. This is
     * only relevant when using <getCanvasContext> for tiles from remote
     * origins and should be set to either 'anonymous' or 'use-credentials'
     * for servers that send Access-Control-Allow-Origin headers with their
     * tiles.
     */
    crossOriginKeyword: null,

    /** TBD 3.0 - reorder the parameters to the init function to remove 
     *             URL. the getUrl() function on the layer gets called on 
     *             each draw(), so no need to specify it here.
     */

    /** 
     * Constructor: OpenLayers.Tile.Image
     * Constructor for a new <OpenLayers.Tile.Image> 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}
     */   
    initialize: function(layer, position, bounds, url, size, options) {
        OpenLayers.Tile.prototype.initialize.apply(this, arguments);

        this.url = url; //deprecated remove me
        
        this.layerAlphaHack = this.layer.alpha && OpenLayers.Util.alphaHack();

        if (this.maxGetUrlLength != null || this.layer.gutter || this.layerAlphaHack) {
            // only create frame if it's needed
            this.frame = document.createElement("div");
            this.frame.style.position = "absolute";
            this.frame.style.overflow = "hidden";
        }
        if (this.maxGetUrlLength != null) {
            OpenLayers.Util.extend(this, OpenLayers.Tile.Image.IFrame);
        }
    },
    
    /** 
     * APIMethod: destroy
     * nullify references to prevent circular references and memory leaks
     */
    destroy: function() {
        if (this.imgDiv)  {
            this.clear();
            this.imgDiv = null;
            this.frame = null;
        }
        // don't handle async requests any more
        this.asyncRequestId = null;
        OpenLayers.Tile.prototype.destroy.apply(this, arguments);
    },
    
    /**
     * Method: draw
     * Check that a tile should be drawn, and draw it.
     * 
     * Returns:
     * {Boolean} Was a tile drawn? Or null if a beforedraw listener returned
     *     false.
     */
    draw: function() {
        var shouldDraw = OpenLayers.Tile.prototype.draw.apply(this, arguments);
        if (shouldDraw) {
            // The layer's reproject option is deprecated.
            if (this.layer != this.layer.map.baseLayer && this.layer.reproject) {
                // getBoundsFromBaseLayer is defined in deprecated.js.
                this.bounds = this.getBoundsFromBaseLayer(this.position);
            }
            if (this.isLoading) {
                //if we're already loading, send 'reload' instead of 'loadstart'.
                this._loadEvent = "reload";
            } else {
                this.isLoading = true;
                this._loadEvent = "loadstart";
            }
            this.renderTile();
            this.positionTile();
        } else if (shouldDraw === false) {
            this.unload();
        }
        return shouldDraw;
    },
    
    /**
     * Method: renderTile
     * Internal function to actually initialize the image tile,
     *     position it correctly, and set its url.
     */
    renderTile: function() {
        if (this.layer.async) {
            // Asynchronous image requests call the asynchronous getURL method
            // on the layer to fetch an image that covers 'this.bounds'.
            var id = this.asyncRequestId = (this.asyncRequestId || 0) + 1;
            this.layer.getURLasync(this.bounds, function(url) {
                if (id == this.asyncRequestId) {
                    this.url = url;
                    this.initImage();
                }
            }, this);
        } else {
            // synchronous image requests get the url immediately.
            this.url = this.layer.getURL(this.bounds);
            this.initImage();
        }
    },

    /**
     * Method: positionTile
     * Using the properties currenty set on the layer, position the tile correctly.
     * This method is used both by the async and non-async versions of the Tile.Image
     * code.
     */
    positionTile: function() {
        var style = this.getTile().style,
            size = this.frame ? this.size :
                this.layer.getImageSize(this.bounds),
            ratio = 1;
        if (this.layer instanceof OpenLayers.Layer.Grid) {
            ratio = this.layer.getServerResolution() / this.layer.map.getResolution();
        }
        style.left = this.position.x + "px";
        style.top = this.position.y + "px";
        style.width = Math.round(ratio * size.w) + "px";
        style.height = Math.round(ratio * size.h) + "px";
    },

    /** 
     * Method: clear
     * Remove the tile from the DOM, clear it of any image related data so that
     * it can be reused in a new location.
     */
    clear: function() {
        OpenLayers.Tile.prototype.clear.apply(this, arguments);
        var img = this.imgDiv;
        if (img) {
            var tile = this.getTile();
            if (tile.parentNode === this.layer.div) {
                this.layer.div.removeChild(tile);
            }
            this.setImgSrc();
            if (this.layerAlphaHack === true) {
                img.style.filter = "";
            }
            OpenLayers.Element.removeClass(img, "olImageLoadError");
        }
        this.canvasContext = null;
    },
    
    /**
     * Method: getImage
     * Returns or creates and returns the tile image.
     */
    getImage: function() {
        if (!this.imgDiv) {
            this.imgDiv = OpenLayers.Tile.Image.IMAGE.cloneNode(false);

            var style = this.imgDiv.style;
            if (this.frame) {
                var left = 0, top = 0;
                if (this.layer.gutter) {
                    left = this.layer.gutter / this.layer.tileSize.w * 100;
                    top = this.layer.gutter / this.layer.tileSize.h * 100;
                }
                style.left = -left + "%";
                style.top = -top + "%";
                style.width = (2 * left + 100) + "%";
                style.height = (2 * top + 100) + "%";
            }
            style.visibility = "hidden";
            style.opacity = 0;
            if (this.layer.opacity < 1) {
                style.filter = 'alpha(opacity=' +
                               (this.layer.opacity * 100) +
                               ')';
            }
            style.position = "absolute";
            if (this.layerAlphaHack) {
                // move the image out of sight
                style.paddingTop = style.height;
                style.height = "0";
                style.width = "100%";
            }
            if (this.frame) {
                this.frame.appendChild(this.imgDiv);
            }
        }

        return this.imgDiv;
    },
    
    /**
     * APIMethod: setImage
     * Sets the image element for this tile. This method should only be called
     * from beforeload listeners.
     *
     * Parameters
     * img - {HTMLImageElement} The image to use for this tile.
     */
    setImage: function(img) {
        this.imgDiv = img;
    },

    /**
     * Method: initImage
     * Creates the content for the frame on the tile.
     */
    initImage: function() {
        if (!this.url && !this.imgDiv) {
            // fast path out - if there is no tile url and no previous image
            this.isLoading = false;
            return;
        }
        this.events.triggerEvent('beforeload');
        this.layer.div.appendChild(this.getTile());
        this.events.triggerEvent(this._loadEvent);
        var img = this.getImage();
        var src = img.getAttribute('src') || '';
        if (this.url && OpenLayers.Util.isEquivalentUrl(src, this.url)) {
            this._loadTimeout = window.setTimeout(
                OpenLayers.Function.bind(this.onImageLoad, this), 0
            );
        } else {
            this.stopLoading();
            if (this.crossOriginKeyword) {
                img.removeAttribute("crossorigin");
            }
            OpenLayers.Event.observe(img, "load",
                OpenLayers.Function.bind(this.onImageLoad, this)
            );
            OpenLayers.Event.observe(img, "error",
                OpenLayers.Function.bind(this.onImageError, this)
            );
            this.imageReloadAttempts = 0;
            this.setImgSrc(this.url);
        }
    },
    
    /**
     * Method: setImgSrc
     * Sets the source for the tile image
     *
     * Parameters:
     * url - {String} or undefined to hide the image
     */
    setImgSrc: function(url) {
        var img = this.imgDiv;
        if (url) {
            img.style.visibility = 'hidden';
            img.style.opacity = 0;
            // don't set crossOrigin if the url is a data URL
            if (this.crossOriginKeyword) {
                if (url.substr(0, 5) !== 'data:') {
                    img.setAttribute("crossorigin", this.crossOriginKeyword);
                } else {
                    img.removeAttribute("crossorigin");
                }
            }
            img.src = url;
        } else {
            // Remove reference to the image, and leave it to the browser's
            // caching and garbage collection.
            this.stopLoading();
            this.imgDiv = null;
            if (img.parentNode) {
                img.parentNode.removeChild(img);
            }
        }
    },
    
    /**
     * Method: getTile
     * Get the tile's markup.
     *
     * Returns:
     * {DOMElement} The tile's markup
     */
    getTile: function() {
        return this.frame ? this.frame : this.getImage();
    },

    /**
     * Method: createBackBuffer
     * Create a backbuffer for this tile. A backbuffer isn't exactly a clone
     * of the tile's markup, because we want to avoid the reloading of the
     * image. So we clone the frame, and steal the image from the tile.
     *
     * Returns:
     * {DOMElement} The markup, or undefined if the tile has no image
     * or if it's currently loading.
     */
    createBackBuffer: function() {
        if (!this.imgDiv || this.isLoading) {
            return;
        }
        var backBuffer;
        if (this.frame) {
            backBuffer = this.frame.cloneNode(false);
            backBuffer.appendChild(this.imgDiv);
        } else {
            backBuffer = this.imgDiv;
        }
        this.imgDiv = null;
        return backBuffer;
    },

    /**
     * Method: onImageLoad
     * Handler for the image onload event
     */
    onImageLoad: function() {
        var img = this.imgDiv;
        this.stopLoading();
        img.style.visibility = 'inherit';
        img.style.opacity = this.layer.opacity;
        this.isLoading = false;
        this.canvasContext = null;
        this.events.triggerEvent("loadend");

        if (this.layerAlphaHack === true) {
            img.style.filter =
                "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='" +
                img.src + "', sizingMethod='scale')";
        }
    },
    
    /**
     * Method: onImageError
     * Handler for the image onerror event
     */
    onImageError: function() {
        var img = this.imgDiv;
        if (img.src != null) {
            this.imageReloadAttempts++;
            if (this.imageReloadAttempts <= OpenLayers.IMAGE_RELOAD_ATTEMPTS) {
                this.setImgSrc(this.layer.getURL(this.bounds));
            } else {
                OpenLayers.Element.addClass(img, "olImageLoadError");
                this.events.triggerEvent("loaderror");
                this.onImageLoad();
            }
        }
    },
    
    /**
     * Method: stopLoading
     * Stops a loading sequence so <onImageLoad> won't be executed.
     */
    stopLoading: function() {
        OpenLayers.Event.stopObservingElement(this.imgDiv);
        window.clearTimeout(this._loadTimeout);
        delete this._loadTimeout;
    },

    /**
     * APIMethod: getCanvasContext
     * Returns a canvas context associated with the tile image (with
     * the image drawn on it).
     * Returns undefined if the browser does not support canvas, if
     * the tile has no image or if it's currently loading.
     *
     * The function returns a canvas context instance but the
     * underlying canvas is still available in the 'canvas' property:
     * (code)
     * var context = tile.getCanvasContext();
     * if (context) {
     *     var data = context.canvas.toDataURL('image/jpeg');
     * }
     * (end)
     *
     * Returns:
     * {Boolean}
     */
    getCanvasContext: function() {
        if (OpenLayers.CANVAS_SUPPORTED && this.imgDiv && !this.isLoading) {
            if (!this.canvasContext) {
                var canvas = document.createElement("canvas");
                canvas.width = this.size.w;
                canvas.height = this.size.h;
                this.canvasContext = canvas.getContext("2d");
                this.canvasContext.drawImage(this.imgDiv, 0, 0);
            }
            return this.canvasContext;
        }
    },

    CLASS_NAME: "OpenLayers.Tile.Image"

});

/** 
 * Constant: OpenLayers.Tile.Image.IMAGE
 * {HTMLImageElement} The image for a tile.
 */
OpenLayers.Tile.Image.IMAGE = (function() {
    var img = new Image();
    img.className = "olTileImage";
    // avoid image gallery menu in IE6
    img.galleryImg = "no";
    return img;
}());