Merge pull request #58790 from elpaso/bugfix-gh57422-server-cascading-legend-size

[server] WMS GetLegendGr.. cascading size

python/PyQt6/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in

@@ -661,6 +661,14 @@ Constructor for QgsWmsLegendNode.
     virtual void invalidateMapBasedData();
 
 
+    QImage getLegendGraphicBlocking( ) const;
+%Docstring
+Fetches the image from the server and returns it.
+
+.. versionadded:: 3.40
+%End
+
+
     SIP_PYOBJECT __repr__();
 %MethodCode
     QString str = QStringLiteral( "<QgsWmsLegendNode: \"%1\">" ).arg( sipCpp->data( Qt::DisplayRole ).toString() );

python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in

@@ -661,6 +661,14 @@ Constructor for QgsWmsLegendNode.
     virtual void invalidateMapBasedData();
 
 
+    QImage getLegendGraphicBlocking( ) const;
+%Docstring
+Fetches the image from the server and returns it.
+
+.. versionadded:: 3.40
+%End
+
+
     SIP_PYOBJECT __repr__();
 %MethodCode
     QString str = QStringLiteral( "<QgsWmsLegendNode: \"%1\">" ).arg( sipCpp->data( Qt::DisplayRole ).toString() );

src/core/layertree/qgslayertreemodellegendnode.cpp

@@ -1462,6 +1462,11 @@ void QgsWmsLegendNode::invalidateMapBasedData()
   emit dataChanged();
 }
 
+QImage QgsWmsLegendNode::getLegendGraphicBlocking() const
+{
+  return getLegendGraphic( true );
+}
+
 // -------------------------------------------------------------------------
 
 QgsDataDefinedSizeLegendNode::QgsDataDefinedSizeLegendNode( QgsLayerTreeLayer *nodeLayer, const QgsDataDefinedSizeLegend &settings, QObject *parent )

src/core/layertree/qgslayertreemodellegendnode.h

@@ -747,6 +747,13 @@ class CORE_EXPORT QgsWmsLegendNode : public QgsLayerTreeModelLegendNode
 
     void invalidateMapBasedData() override;
 
+    /**
+     *  Fetches the image from the server and returns it.
+     *  \since QGIS 3.40
+     */
+    QImage getLegendGraphicBlocking( ) const;
+
+
 #ifdef SIP_RUN
     SIP_PYOBJECT __repr__();
     % MethodCode
@@ -763,7 +770,7 @@ class CORE_EXPORT QgsWmsLegendNode : public QgsLayerTreeModelLegendNode
 
   private:
 
-    // Lazily initializes mImage
+    // Lazy loading of the image
     QImage getLegendGraphic( bool synchronous = false ) const;
 
     QImage renderMessage( const QString &msg ) const;

src/server/services/wms/qgswmsrenderer.cpp

@@ -124,8 +124,36 @@ namespace QgsWms
     QList<QgsMapLayer *> layers = mContext.layersToRender();
     configureLayers( layers );
 
-    // init renderer
+    const qreal dpmm = mContext.dotsPerMm();
+
     QgsLegendSettings settings = legendSettings();
+
+    // adjust the size settings if there any WMS cascading layers to renderer
+    const auto layersToRender = mContext.layersToRender();
+    for ( const auto &layer : std::as_const( layersToRender ) )
+    {
+      // If it is a cascading WMS layer, get legend node image size
+      if ( layer->dataProvider()->name() == QStringLiteral( "wms" ) )
+      {
+        if ( QgsWmsLegendNode *layerNode = qobject_cast<QgsWmsLegendNode *>( model.findLegendNode( layer->id(), QString() ) ) )
+        {
+          const auto image { layerNode->getLegendGraphicBlocking( ) };
+          if ( ! image.isNull() )
+          {
+            // Check that we are not exceeding the maximum size
+            if ( mContext.isValidWidthHeight( image.width(), image.height() ) )
+            {
+              const double w = image.width() / dpmm;
+              const double h = image.height() / dpmm;
+              const QSizeF newWmsSize { w, h };
+              settings.setWmsLegendSize( newWmsSize );
+            }
+          }
+        }
+      }
+    }
+
+    // init renderer
     QgsLegendRenderer renderer( &model, settings );
 
     // create context
@@ -146,7 +174,6 @@ namespace QgsWms
 
     // create image according to context
     std::unique_ptr<QImage> image;
-    const qreal dpmm = mContext.dotsPerMm();
     const QSizeF minSize = renderer.minimumSize( &context );
     const QSize size( static_cast<int>( minSize.width() * dpmm ), static_cast<int>( minSize.height() * dpmm ) );
     if ( !mContext.isValidWidthHeight( size.width(), size.height() ) )