Allow adding a new part to multipart geometries

app/maptools/recordingmaptool.cpp

@@ -1150,6 +1150,36 @@ void RecordingMapTool::cancelGrab()
   setActiveVertex( Vertex() );
 }
 
+void RecordingMapTool::startDigitizingNewPart()
+{
+  // if maptool is in GRAB and VIEW state, no part should be added
+  if ( mState == RecordingMapTool::View || mState == RecordingMapTool::Grab )
+  {
+    return;
+  }
+
+  QgsAbstractGeometry *geom = mRecordedGeometry.get();
+  if ( QgsGeometryCollection *collection = qgsgeometry_cast<QgsGeometryCollection *>( geom ) )
+  {
+    switch ( mRecordedGeometry.type() )
+    {
+      case Qgis::GeometryType::Line:
+        collection->addGeometry( new QgsLineString() );
+        setActivePartAndRing( collection->partCount() - 1, 0 );
+        break;
+      case Qgis::GeometryType::Polygon:
+        collection->addGeometry( new QgsPolygon( new QgsLineString(), QList<QgsLineString*>() ) );
+        setActivePartAndRing( collection->partCount() - 1, 0 );
+        break;
+      case Qgis::GeometryType::Point:
+      // MultiPoints do not need an empty placeholder part, new point part is directly appended when digitizing
+      case Qgis::GeometryType::Unknown:
+      case Qgis::GeometryType::Null:
+        break;
+    }
+  }
+}
+
 double RecordingMapTool::pixelsToMapUnits( double numPixels )
 {
   QgsRenderContext context = QgsRenderContext::fromMapSettings( mapSettings()->mapSettings() );

app/maptools/recordingmaptool.h

@@ -184,6 +184,13 @@ class RecordingMapTool : public AbstractMapTool
 
     Q_INVOKABLE void cancelGrab();
 
+    /**
+     * When this is called on a multipart geometry, a new empty part will be added to the geometry and
+     * activePart will be set to that new last part.
+     * For MultiPoints and singlepart geometries no new empty part will be added.
+     */
+    Q_INVOKABLE void startDigitizingNewPart();
+
     // Getters / setters
     bool centeredToGPS() const;
     void setCenteredToGPS( bool newCenteredToGPS );

app/qml/map/MMMapController.qml

@@ -814,17 +814,22 @@ Item {
               return "invisible"
 
             if (internal.splitGeometryButtonVisible) {
-              if (!internal.redrawGeometryButtonVisible && !internal.streamingModeButtonVisible)
+              if (!internal.redrawGeometryButtonVisible && !internal.streamingModeButtonVisible && !internal.addPartButtonVisible)
                 return "split"
             }
 
+            if (internal.addPartButtonVisible) {
+              if (!internal.splitGeometryButtonVisible && !internal.streamingModeButtonVisible && !internal.redrawGeometryButtonVisible)
+                return "addPart"
+            }
+
             if (internal.redrawGeometryButtonVisible) {
-              if (!internal.splitGeometryButtonVisible && !internal.streamingModeButtonVisible)
+              if (!internal.splitGeometryButtonVisible && !internal.streamingModeButtonVisible && !internal.addPartButtonVisible)
                 return "redraw"
             }
 
             if (internal.streamingModeButtonVisible) {
-              if (!internal.redrawGeometryButtonVisible && !internal.splitGeometryButtonVisible)
+              if (!internal.redrawGeometryButtonVisible && !internal.splitGeometryButtonVisible && !internal.addPartButtonVisible)
                 return "stream"
             }
             return "menu"
@@ -834,6 +839,9 @@ Item {
             if (actionState === "split")
               return __style.splitGeometryIcon
 
+            if (actionState === "addPart")
+              return __style.plusIcon
+
             if (actionState === "redraw")
               return __style.redrawGeometryIcon
 
@@ -847,6 +855,9 @@ Item {
             if (actionState === "split")
               return root.toggleSplitting()
 
+            if (actionState === "addPart")
+              return root.toggleAddPart()
+
             if (actionState === "redraw")
               return root.toggleRedraw()
 
@@ -977,6 +988,18 @@ Item {
           }
         }
 
+        MMListDelegate {
+          text: qsTr( "Add part" )
+          leftContent: MMIcon { source: __style.plusIcon }
+
+          visible: internal.addPartButtonVisible
+
+          onClicked: {
+            root.toggleAddPart()
+            moreToolsMenu.close()
+          }
+        }
+
         MMListDelegate {
           text: qsTr( "Redraw geometry" )
           leftContent: MMIcon { source: __style.redrawGeometryIcon }
@@ -1262,6 +1285,7 @@ Item {
 
     // visibility of buttons in "more" menu
     property bool splitGeometryButtonVisible: !internal.isPointLayer && !root.isStreaming && root.state === "edit"
+    property bool addPartButtonVisible: internal.isMultiPartLayer && !root.isStreaming && root.state === "edit"
     property bool redrawGeometryButtonVisible: root.state === "edit"
     property bool streamingModeButtonVisible: !internal.isPointLayer || internal.isMultiPartLayer
 
@@ -1323,6 +1347,24 @@ Item {
     }
   }
 
+  function toggleAddPart() {
+    addPart( internal.featurePairToEdit )
+  }
+
+  function addPart( featurepair) {
+    __activeProject.setActiveLayer( featurepair.layer )
+    root.centerToPair( featurepair )
+    root.showInfoTextMessage( qsTr( "Add new part to the geometry" ) )
+
+    internal.featurePairToEdit = featurepair
+
+    // You should be already in state == "edit"
+    if ( recordingToolsLoader.active ) {
+      recordingToolsLoader.item.recordingMapTool.state = MM.RecordingMapTool.Record
+      recordingToolsLoader.item.recordingMapTool.startDigitizingNewPart()
+    }
+  }
+
   function toggleSplitting() {
     split(internal.featurePairToEdit)
   }