Add rendering extent information to expression context

Author: m-kuhn

src/core/qgsexpressioncontext.cpp

@@ -702,6 +702,11 @@ QgsExpressionContextScope* QgsExpressionContextUtils::mapSettingsScope( const Qg
   scope->addVariable( QgsExpressionContextScope::StaticVariable( "map_id", "canvas", true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( "map_rotation", mapSettings.rotation(), true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( "map_scale", mapSettings.scale(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "map_extent_width", mapSettings.extent().width() ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "map_extent_height", mapSettings.extent().height() ) );
+  QgsGeometry* centerPoint = QgsGeometry::fromPoint( mapSettings.visibleExtent().center() );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( "map_extent_center", QVariant::fromValue( *centerPoint ), true ) );
+  delete centerPoint;
 
   return scope;
 }