WMSLayer loads map tiles from a Web Map Server.

class WMSLayer extends TileLayer {

 String _serviceUrl;
 final List<String> _layers = [];
 Map<String, String> _defaultParameters;

 _initParameters(Map userParameters) {
   if (userParameters == null) {
     userParameters = {};
   }

   _defaultParameters = new Map();
   // normalize case
   userParameters.keys.forEach((k) {
     _defaultParameters[k.toUpperCase()] = userParameters[k];
   });
   if (!_defaultParameters.containsKey("SERVICE")) {
     _defaultParameters["SERVICE"] = "WMS";
   }
   if (!_defaultParameters.containsKey("VERSION")) {
     _defaultParameters["VERSION"] = "1.0.0";
   }
   if (!_defaultParameters.containsKey("FORMAT")) {
     _defaultParameters["FORMAT"] = "image/png";
   }
   if (!_defaultParameters.containsKey("SRS")) {
     _defaultParameters["SRS"] = "EPSG:4326";
   }
 }
 /**
  * [serviceUrl] is base URL of the WMS server.
  *
  * [layers] is either a single layer name or a list of layer
  * names.
  *
  * [parameters] is a map of WMS request parameters.
  * 
  * [renderer] is one of the renderer values supported by
  * [TileLayer].
  *
  * ##Examples
  *      var layer1 = new WmsLayer(
  *        serviceUrl: "https://wms.geo.admin.ch?",
  *        layers: "ch.are.gemeindetypen"
  *      );
  *
  *      var layer2 = new WmsLayer(
  *        serviceUrl: "https://wms.geo.admin.ch?",
  *        layers: ["ch.are.gemeindetypen", "ch.are.alpenkonvention"],
  *        parameters: {
  *          "FORMAT": "image/jpeg"
  *        }
  *      );
  */
 WMSLayer({String serviceUrl, layers, Map parameters, renderer})
   : super(renderer:renderer)
 {
     if (?serviceUrl) this.serviceUrl = serviceUrl;
     if (?layers) this.layers = layers;
     _initParameters(parameters);
 }

 /// the layer(s) to be loaded from the WMS server
 List<String> get layers => _layers;

 /**
  * Sets the layer(s) to be retrieved from the WMS server.
  *
  * ## Possible values
  * * [String] - a single layer
  * * [List] - a list of layer names
  */
 void set layers(value) {
   if (value is String) {
     _layers.clear();
     _layers.add(value);
   } else if (value is List) {
     _layers.clear();
     _layers.addAll(value);
   } else {
     throw new ArgumentError("expected String or list thereof, got $value");
   }
 }

 /// sets the service URL
 void set serviceUrl(String value) {
   if (value != null && value.endsWith("?")) {
     value = value.substring(0, value.length -1);
   }
   _serviceUrl = value;
 }

 /// the URL of the WMS server or null, if the server URL
 /// isn't configured yet
 String get serviceUrl => _serviceUrl;

 /**
  * Builds the tile bounding box for tile ([x],[y]) in geographic
  * coordinates.
  */
 //TODO: Order of components in the bbox string changed in WMS 1.3.0?
 String _buildGeographicTileBBox(int x, int y, int zoom) {
   var size = tileSize;
   var tx = x * tileSize.width;
   var ty = y * tileSize.height + (tileSize.height - 1);
   var min = map.mapToEarth(map.zoomPlaneToMap(new Point2D(tx, ty)));

   tx = tx + tileSize.width - 1;
   ty = y * tileSize.height;
   var max = map.mapToEarth(map.zoomPlaneToMap(new Point2D(tx, ty)));
   return "${min.lon},${min.lat},${max.lon},${max.lat}";
 }

 /**
  * Indicates whether the bounding box of a WMS `GetMap`request is
  * expressed in geographic or in projected coordinates.
  *
  * * if false, the bounding box is expressed in geographic coordinates,
  *   i.e. in WGS84 aka
  *   [EPSG:4326](http://spatialreference.org/ref/epsg/4326/)
  *
  * * if true, the bounding box is expressed in projected coordinates,
  *   that is coordinate reference system configured on the
  *   map viewport, see [MapViewport.crs].
  *
  * Default value is false.
  */
 bool useProjectedCoordinates = false;

 /**
  * Builds the tile bounding box for tile ([x],[y]) in projected
  * coordinates
  */
 //TODO: Order of components in the bbox string changed in WMS 1.3.0?
 String _buildProjectedTileBBox(int x, int y, int zoom) {
   var tx = x * tileSize.width;
   var ty = y * tileSize.height + (tileSize.height - 1);
   var min = map.zoomPlaneToMap(new Point2D(tx, ty));

   tx = tx + tileSize.width - 1;
   ty = y * tileSize.height;
   var max = map.zoomPlaneToMap(new Point2D(tx, ty));
   return "${min.x},${min.y},${max.x},${max.y}";
 }

 @override
 String bindTileToUrl(int x, int y, int zoom) {
   var ts = tileSize;
   var parameters = new Map.from(_defaultParameters);
   parameters["REQUEST"] = "GetMap";
   parameters["LAYERS"] = _layers.join(",");
   parameters["WIDTH"] = ts.width.toString();
   parameters["HEIGHT"] = ts.height.toString();
   if (useProjectedCoordinates) {
     parameters["BBOX"] = _buildProjectedTileBBox(x,y,zoom);
     parameters["SRS"] = _map.crs.code;
   } else {
     parameters["BBOX"] = _buildGeographicTileBBox(x,y,zoom);
     parameters["SRS"] = "EPSG:4326";
   }

   var query = parameters.keys.map((k) => "$k=${parameters[k]}").join("&");
   var url = "$_serviceUrl?$query";
   return url;
 }

 @override
 void render() {
   if (_serviceUrl == null) {
     print("WARNING: can't render, serviceUrl not defined");
     return;
   }
   if (_layers.isEmpty) {
     print("WARNING: can't render, no layers defined");
     return;
   }
   super.render();
 }
}