Add serverType option to ol.source.ImageWMS constructor

src/objectliterals.jsdoc

@@ -516,6 +516,9 @@
  * @property {ol.Extent|undefined} extent Extent.
  * @property {boolean|undefined} hidpi Use the `ol.Map#devicePixelRatio` value when
  *     requesting the image from the remote server. Default is `true`.
+ * @property {ol.source.wms.ServerType|undefined} serverType The type of the remote WMS
+ *     server: `mapserver`, `geoserver` or `qgis`. Only needed if `hidpi` is `true`.
+ *     Default is `undefined`.
  * @property {boolean|undefined} useOverlay If `true`, will use
  *     `GETDYNAMICMAPOVERLAYIMAGE`.
  * @property {ol.proj.ProjectionLike} projection Projection.

src/ol/source/imagewmssource.js

@@ -38,6 +38,12 @@ ol.source.ImageWMS = function(options) {
     imageUrlFunction: imageUrlFunction
   });
 
+  /**
+   * @private
+   * @type {ol.source.wms.ServerType|undefined}
+   */
+  this.serverType_ = options.serverType;
+
   /**
    * @private
    * @type {boolean}
@@ -92,6 +98,11 @@ ol.source.ImageWMS.prototype.getImage =
   var height = (extent[3] - extent[1]) / resolution;
   var size = [width * pixelRatio, height * pixelRatio];
 
+  if (goog.isDef(this.serverType_) && pixelRatio > 1) {
+    var param = ol.source.wms.getDpiParam(this.serverType_, pixelRatio);
+    goog.object.extend(this.params_, param);
+  }
+
   this.image_ = this.createImage(
       extent, resolution, pixelRatio, size, projection);
   return this.image_;

src/ol/source/wmssource.js

@@ -1,9 +1,20 @@
 goog.provide('ol.source.wms');
 
+goog.require('goog.asserts');
 goog.require('goog.object');
 goog.require('goog.uri.utils');
 
 
+/**
+ * @enum {string}
+ */
+ol.source.wms.ServerType = {
+  MAPSERVER: 'mapserver',
+  GEOSERVER: 'geoserver',
+  QGIS: 'qgis'
+};
+
+
 /**
  * @param {string} baseUrl WMS base URL.
  * @param {Object.<string, string|number>} params Request parameters.
@@ -12,8 +23,7 @@ goog.require('goog.uri.utils');
  * @param {ol.proj.Projection} projection Projection.
  * @return {string} WMS GetMap request URL.
  */
-ol.source.wms.getUrl =
-    function(baseUrl, params, extent, size, projection) {
+ol.source.wms.getUrl = function(baseUrl, params, extent, size, projection) {
   var baseParams = {
     'SERVICE': 'WMS',
     'VERSION': '1.3.0',
@@ -40,3 +50,23 @@ ol.source.wms.getUrl =
 
   return goog.uri.utils.appendParamsFromMap(baseUrl, baseParams);
 };
+
+
+/**
+ * @param {ol.source.wms.ServerType} serverType Server name.
+ * @param {number} pixelRatio Pixel ratio.
+ * @return {Object.<string, string>}
+ */
+ol.source.wms.getDpiParam = function(serverType, pixelRatio) {
+  var param = {};
+  if (serverType == ol.source.wms.ServerType.MAPSERVER) {
+    param['MAP_RESOLUTION'] = 90 * pixelRatio;
+  } else if (serverType == ol.source.wms.ServerType.GEOSERVER) {
+    param['FORMAT_OPTION'] = 'dpi:' + 90 * pixelRatio;
+  } else if (serverType == ol.source.wms.ServerType.QGIS) {
+    param['DPI'] = 90 * pixelRatio;
+  } else {
+    goog.asserts.fail();
+  }
+  return param;
+};