WMS server: Support <NamedStyle> in SLD

When using <NamedStyle> make sure the passed SLD XML has attribute units="mm"
in the root <StyledLayerDescriptor> tag. Otherwise the WMS server applies scaling
as if all sizes were in pixels. The correct approach would be to just scale
sizes when loading symbols from SLD - not to apply such scaling globally

This code has been funded by Tuscany Region (Italy) - SITA (CIG: 6002233F59) and commissioned to Gis3W s.a.s.

Author: wonder-sk

src/server/qgssldconfigparser.cpp

@@ -256,6 +256,18 @@ QList<QgsMapLayer*> QgsSLDConfigParser::mapLayerFromStyle( const QString& lName,
         }
       }
     }
+
+    // try with a predefined named style
+    QDomElement namedStyleElement = findNamedStyleElement( namedLayerElemList[i], styleName );
+    if ( !namedStyleElement.isNull() )
+    {
+      fallbackLayerList = mFallbackParser->mapLayerFromStyle( lName, styleName, false );
+      if ( fallbackLayerList.size() > 0 )
+      {
+        resultList << fallbackLayerList;
+        return resultList;
+      }
+    }
   }
 
   QDomElement userLayerElement = findUserLayerElement( lName );
@@ -799,6 +811,27 @@ QDomElement QgsSLDConfigParser::findUserStyleElement( const QDomElement& userLay
   return defaultResult;
 }
 
+QDomElement QgsSLDConfigParser::findNamedStyleElement( const QDomElement& layerElement, const QString& styleName ) const
+{
+  QDomElement defaultResult;
+  if ( !layerElement.isNull() )
+  {
+    QDomNodeList styleList = layerElement.elementsByTagName( "NamedStyle" );
+    for ( int i = 0; i < styleList.size(); ++i )
+    {
+      QDomNodeList nameList = styleList.item( i ).toElement().elementsByTagName( "Name" );
+      if ( nameList.size() > 0 )
+      {
+        if ( nameList.item( 0 ).toElement().text() == styleName )
+        {
+          return styleList.item( i ).toElement();
+        }
+      }
+    }
+  }
+  return defaultResult;
+}
+
 QgsFeatureRendererV2* QgsSLDConfigParser::rendererFromUserStyle( const QDomElement& userStyleElement, QgsVectorLayer* vec ) const
 {
   if ( !vec || userStyleElement.isNull() )

src/server/qgssldconfigparser.h

@@ -159,6 +159,9 @@ class QgsSLDConfigParser : public QgsWMSConfigParser
     /**Returns the <UserStyle> node of a given <UserLayer> or a null node in case of failure*/
     QDomElement findUserStyleElement( const QDomElement& userLayerElement, const QString& styleName ) const;
 
+    /**Returns the <NamedStyle> node of a given <NamedLayer> or a null node in case of failure*/
+    QDomElement findNamedStyleElement( const QDomElement& layerElement, const QString& styleName ) const;
+
     /**Creates a Renderer from a UserStyle SLD node. Returns 0 in case of error*/
     QgsFeatureRendererV2* rendererFromUserStyle( const QDomElement& userStyleElement, QgsVectorLayer* vec ) const;