Add convenient syntax for specifying multiple tile servers

src/ol/tile/tileurlfunction.js

@@ -16,15 +16,28 @@ ol.TileUrlFunctionType;
  * @return {ol.TileUrlFunctionType} Tile URL function.
  */
 ol.TileUrlFunction.createFromTemplate = function(template) {
-  return function(tileCoord) {
+  var match =
-    if (goog.isNull(tileCoord)) {
+      /\{(\d)-(\d)\}/.exec(template) || /\{([a-z])-([a-z])\}/.exec(template);
-      return undefined;
+  if (match) {
-    } else {
+    var templates = [];
-      return template.replace('{z}', tileCoord.z)
+    var startCharCode = match[1].charCodeAt(0);
-                     .replace('{x}', tileCoord.x)
+    var stopCharCode = match[2].charCodeAt(0);
-                     .replace('{y}', tileCoord.y);
+    var charCode;
+    for (charCode = startCharCode; charCode <= stopCharCode; ++charCode) {
+      templates.push(template.replace(match[0], String.fromCharCode(charCode)));
     }
-  };
+    return ol.TileUrlFunction.createFromTemplates(templates);
+  } else {
+    return function(tileCoord) {
+      if (goog.isNull(tileCoord)) {
+        return undefined;
+      } else {
+        return template.replace('{z}', tileCoord.z)
+                       .replace('{x}', tileCoord.x)
+                       .replace('{y}', tileCoord.y);
+      }
+    };
+  }
 };