openlayers/src/ol/tile.js

Build tools and sources for developing OpenLayers based mapping applications

goog.provide('ol.Tile');

goog.require('ol');
goog.require('ol.events.EventTarget');
goog.require('ol.events.EventType');


/**
 * @classdesc
 * Base class for tiles.
 *
 * @constructor
 * @extends {ol.events.EventTarget}
 * @param {ol.TileCoord} tileCoord Tile coordinate.
 * @param {ol.Tile.State} state State.
 */
ol.Tile = function(tileCoord, state) {

  ol.events.EventTarget.call(this);

  /**
   * @type {ol.TileCoord}
   */
  this.tileCoord = tileCoord;

  /**
   * @protected
   * @type {ol.Tile.State}
   */
  this.state = state;

  /**
   * An "interim" tile for this tile. The interim tile may be used while this
   * one is loading, for "smooth" transitions when changing params/dimensions
   * on the source.
   * @type {ol.Tile}
   */
  this.interimTile = null;

  /**
   * A key assigned to the tile. This is used by the tile source to determine
   * if this tile can effectively be used, or if a new tile should be created
   * and this one be used as an interim tile for this new tile.
   * @type {string}
   */
  this.key = '';

};
ol.inherits(ol.Tile, ol.events.EventTarget);


/**
 * @protected
 */
ol.Tile.prototype.changed = function() {
  this.dispatchEvent(ol.events.EventType.CHANGE);
};


/**
 * Get the HTML image element for this tile (may be a Canvas, Image, or Video).
 * @abstract
 * @return {HTMLCanvasElement|HTMLImageElement|HTMLVideoElement} Image.
 */
ol.Tile.prototype.getImage = function() {};


/**
 * @return {string} Key.
 */
ol.Tile.prototype.getKey = function() {
  return this.key + '/' + this.tileCoord;
};

/**
 * Get the interim tile most suitable for rendering using the chain of interim
 * tiles. This corresponds to the  most recent tile that has been loaded, if no
 * such tile exists, the original tile is returned.
 * @return {!ol.Tile} Best tile for rendering.
 */
ol.Tile.prototype.getInterimTile = function() {
  if (!this.interimTile) {
    //empty chain
    return this;
  }
  var tile = this.interimTile;

  // find the first loaded tile and return it. Since the chain is sorted in
  // decreasing order of creation time, there is no need to search the remainder
  // of the list (all those tiles correspond to older requests and will be
  // cleaned up by refreshInterimChain)
  do {
    if (tile.getState() == ol.Tile.State.LOADED) {
      return tile;
    }
    tile = tile.interimTile;
  } while (tile);

  // we can not find a better tile
  return this;
};

/**
 * Goes through the chain of interim tiles and discards sections of the chain
 * that are no longer relevant.
 */
ol.Tile.prototype.refreshInterimChain = function() {
  if (!this.interimTile) {
    return;
  }

  var tile = this.interimTile;
  var prev = this;

  do {
    if (tile.getState() == ol.Tile.State.LOADED) {
      //we have a loaded tile, we can discard the rest of the list
      //we would could abort any LOADING tile request
      //older than this tile (i.e. any LOADING tile following this entry in the chain)
      tile.interimTile = null;
      break;
    } else if (tile.getState() == ol.Tile.State.LOADING) {
      //keep this LOADING tile any loaded tiles later in the chain are
      //older than this tile, so we're still interested in the request
      prev = tile;
    } else if (tile.getState() == ol.Tile.State.IDLE) {
      //the head of the list is the most current tile, we don't need
      //to start any other requests for this chain
      prev.interimTile = tile.interimTile;
    } else {
      prev = tile;
    }
    tile = prev.interimTile;
  } while (tile);
};

/**
 * Get the tile coordinate for this tile.
 * @return {ol.TileCoord} The tile coordinate.
 * @api
 */
ol.Tile.prototype.getTileCoord = function() {
  return this.tileCoord;
};


/**
 * @return {ol.Tile.State} State.
 */
ol.Tile.prototype.getState = function() {
  return this.state;
};


/**
 * Load the image or retry if loading previously failed.
 * Loading is taken care of by the tile queue, and calling this method is
 * only needed for preloading or for reloading in case of an error.
 * @abstract
 * @api
 */
ol.Tile.prototype.load = function() {};


/**
 * @enum {number}
 */
ol.Tile.State = {
  IDLE: 0,
  LOADING: 1,
  LOADED: 2,
  ERROR: 3,
  EMPTY: 4,
  ABORT: 5
};