Add drawLegend method for json

src/core/layertree/qgslayertreemodellegendnode.cpp

@@ -71,6 +71,11 @@ QgsLayerTreeModelLegendNode::ItemMetrics QgsLayerTreeModelLegendNode::draw( cons
   return im;
 }
 
+void QgsLayerTreeModelLegendNode::draw( const QgsLegendSettings &settings, QJsonObject &json )
+{
+  drawSymbolText( settings, json );
+  json[ "symbol" ] = "TODO";
+}
 
 QSizeF QgsLayerTreeModelLegendNode::drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const
 {
@@ -129,6 +134,13 @@ QSizeF QgsLayerTreeModelLegendNode::drawSymbolText( const QgsLegendSettings &set
   return labelSize;
 }
 
+void QgsLayerTreeModelLegendNode::drawSymbolText( const QgsLegendSettings &settings, QJsonObject &json ) const
+{
+  QgsExpressionContext tempContext;
+  const QString text = data( Qt::DisplayRole ).toString();
+  json[ "title" ] = text;
+}
+
 // -------------------------------------------------------------------------
 
 QgsSymbolLegendNode::QgsSymbolLegendNode( QgsLayerTreeLayer *nodeLayer, const QgsLegendSymbolItem &item, QObject *parent )

src/core/layertree/qgslayertreemodellegendnode.h

@@ -110,6 +110,8 @@ class CORE_EXPORT QgsLayerTreeModelLegendNode : public QObject
      */
     virtual ItemMetrics draw( const QgsLegendSettings &settings, ItemContext *ctx );
 
+    void draw( const QgsLegendSettings &settings, QJsonObject &json );
+
     /**
      * Draws symbol on the left side of the item
      * \param settings Legend layout configuration
@@ -128,6 +130,8 @@ class CORE_EXPORT QgsLayerTreeModelLegendNode : public QObject
      */
     virtual QSizeF drawSymbolText( const QgsLegendSettings &settings, ItemContext *ctx, QSizeF symbolSize ) const;
 
+    void drawSymbolText( const QgsLegendSettings &settings, QJsonObject &json ) const;
+
   signals:
     //! Emitted on internal data change so the layer tree model can forward the signal to views
     void dataChanged();

src/core/qgslegendrenderer.cpp

@@ -25,6 +25,7 @@
 #include "qgsvectorlayer.h"
 #include "qgsexpressioncontextutils.h"
 
+#include <QJsonObject>
 #include <QPainter>
 
 
@@ -45,6 +46,79 @@ void QgsLegendRenderer::drawLegend( QPainter *painter )
   paintAndDetermineSize( painter );
 }
 
+void QgsLegendRenderer::drawLegend( QJsonObject &json )
+{
+  QgsLayerTreeGroup *rootGroup = mLegendModel->rootGroup();
+  if ( !rootGroup )
+    return;
+
+  json["title"] = mSettings.title();
+  drawLegend( rootGroup, json );
+}
+
+void QgsLegendRenderer::drawLegend( QgsLayerTreeGroup *nodeGroup, QJsonObject &json )
+{
+  QJsonArray nodes;
+  Q_FOREACH ( QgsLayerTreeNode *node, nodeGroup->children() )
+  {
+    if ( QgsLayerTree::isGroup( node ) )
+    {
+      QgsLayerTreeGroup *nodeGroup = QgsLayerTree::toGroup( node );
+
+      QModelIndex idx = mLegendModel->node2index( nodeGroup );
+      QgsExpressionContext tempContext;
+      const QString text = mLegendModel->data( idx, Qt::DisplayRole ).toString();
+
+      QJsonObject group;
+      group[ "type" ] = "group";
+      group[ "title" ] = text;
+      drawLegend( nodeGroup, group );
+      nodes.append( group );
+    }
+    else if ( QgsLayerTree::isLayer( node ) )
+    {
+      QJsonObject group;
+      group[ "type" ] = "layer";
+
+      QgsLayerTreeLayer *nodeLayer = QgsLayerTree::toLayer( node );
+
+      QString text;
+      if ( nodeLegendStyle( nodeLayer ) != QgsLegendStyle::Hidden )
+      {
+        QModelIndex idx = mLegendModel->node2index( nodeLayer );
+        text = mLegendModel->data( idx, Qt::DisplayRole ).toString();
+      }
+
+      QList<QgsLayerTreeModelLegendNode *> legendNodes = mLegendModel->layerLegendNodes( nodeLayer );
+
+      if ( legendNodes.isEmpty() && mLegendModel->legendFilterMapSettings() )
+        continue;
+
+      if ( legendNodes.count() == 1 )
+      {
+        legendNodes.at( 0 )->draw( mSettings, group );
+        nodes.append( group );
+      }
+      else if ( legendNodes.count() > 1 )
+      {
+        QJsonArray symbols;
+        for ( int j = 0; j < legendNodes.count(); j++ )
+        {
+          QgsLayerTreeModelLegendNode *legendNode = legendNodes.at( j );
+          QJsonObject symbol;
+          legendNode->draw( mSettings, symbol );
+          symbols.append( symbol );
+        }
+        group[ "title" ] = text;
+        group[ "symbols" ] = symbols;
+        nodes.append( group );
+      }
+    }
+  }
+
+  json["nodes"] = nodes;
+}
+
 QSizeF QgsLegendRenderer::paintAndDetermineSize( QPainter *painter )
 {
   return paintAndDetermineSizeInternal( nullptr, painter );

src/core/qgslegendrenderer.h

@@ -21,6 +21,7 @@
 
 class QRectF;
 class QStandardItem;
+class QJsonObject;
 
 class QgsLayerTreeGroup;
 class QgsLayerTreeLayer;
@@ -92,6 +93,8 @@ class CORE_EXPORT QgsLegendRenderer
      */
     void drawLegend( QgsRenderContext &context );
 
+    void drawLegend( QJsonObject &json );
+
     /**
      * Sets the \a style of a \a node.
      *
@@ -232,6 +235,8 @@ class CORE_EXPORT QgsLegendRenderer
      */
     QSizeF drawGroupTitle( QgsLayerTreeGroup *nodeGroup, QPainter *painter = nullptr, QPointF point = QPointF() );
 
+    void drawLegend( QgsLayerTreeGroup *nodeGroup, QJsonObject &json );
+
     /**
      * Draws the legend using the specified render \a context, and returns the actual size of the legend.
      *