Add a settable key for all tile sources

The source's key is used as the key for all tiles in the source.  For URL tile sources, the URL is the key.

src/ol/source/tilesource.js

@@ -67,6 +67,12 @@ ol.source.Tile = function(options) {
    */
   this.tmpSize = [0, 0];
 
+  /**
+   * @private
+   * @type {string}
+   */
+  this.key_ = '';
+
 };
 goog.inherits(ol.source.Tile, ol.source.Source);
 
@@ -144,7 +150,20 @@ ol.source.Tile.prototype.getGutter = function(projection) {
  * @protected
  */
 ol.source.Tile.prototype.getKeyParams = function() {
-  return '';
+  return this.key_;
+};
+
+
+/**
+ * Set the value to be used as the key for all tiles in the source.
+ * @param {string} key The key for tiles.
+ * @protected
+ */
+ol.source.Tile.prototype.setKey = function(key) {
+  if (this.key_ !== key) {
+    this.key_ = key;
+    this.changed();
+  }
 };
 
 

src/ol/source/urltilesource.js

@@ -143,15 +143,16 @@ ol.source.UrlTile.prototype.setTileLoadFunction = function(tileLoadFunction) {
 /**
  * Set the tile URL function of the source.
  * @param {ol.TileUrlFunctionType} tileUrlFunction Tile URL function.
+ * @param {string=} opt_key Optional new tile key for the source.
  * @api
  */
-ol.source.UrlTile.prototype.setTileUrlFunction = function(tileUrlFunction) {
-  // FIXME It should be possible to be more intelligent and avoid clearing the
-  // FIXME cache.  The tile URL function would need to be incorporated into the
-  // FIXME cache key somehow.
-  this.tileCache.clear();
+ol.source.UrlTile.prototype.setTileUrlFunction = function(tileUrlFunction, opt_key) {
   this.tileUrlFunction = tileUrlFunction;
-  this.changed();
+  if (typeof opt_key !== 'undefined') {
+    this.setKey(opt_key);
+  } else {
+    this.changed();
+  }
 };
 
 
@@ -164,7 +165,7 @@ ol.source.UrlTile.prototype.setUrl = function(url) {
   var urls = this.urls = ol.TileUrlFunction.expandUrl(url);
   this.setTileUrlFunction(this.fixedTileUrlFunction ?
       this.fixedTileUrlFunction.bind(this) :
-      ol.TileUrlFunction.createFromTemplates(urls, this.tileGrid));
+      ol.TileUrlFunction.createFromTemplates(urls, this.tileGrid), url);
 };
 
 
@@ -175,9 +176,10 @@ ol.source.UrlTile.prototype.setUrl = function(url) {
  */
 ol.source.UrlTile.prototype.setUrls = function(urls) {
   this.urls = urls;
+  var key = urls.join('\n');
   this.setTileUrlFunction(this.fixedTileUrlFunction ?
       this.fixedTileUrlFunction.bind(this) :
-      ol.TileUrlFunction.createFromTemplates(urls, this.tileGrid));
+      ol.TileUrlFunction.createFromTemplates(urls, this.tileGrid), key);
 };