Implement slave contact groups — label transfer, terminal assignment and UI fixes

sources/qetgraphicsitem/element.h

@@ -62,6 +62,20 @@ class Element : public QetGraphicsItem
             Thumbnail = 64,
             ConductorDefinition = 128};
 
+		/**
+		 * @brief The LinkInfo struct
+		 * Stores link data for element connections.
+		 * For slave elements, group_index indicates which contact group
+		 * of the master this slave is assigned to (-1 = no group assigned).
+		 */
+		struct LinkInfo {
+			QUuid uuid;
+			int group_index = -1;  ///< Index into master's slaveContactGroups, -1 = not assigned
+
+			LinkInfo() = default;
+			LinkInfo(const QUuid &u, int gi = -1) : uuid(u), group_index(gi) {}
+		};
+
 		Element(const ElementsLocation &location,
 			QGraphicsItem * = nullptr,
 			int *state = nullptr,
@@ -181,6 +195,9 @@ class Element : public QetGraphicsItem
 		virtual void initLink(QETProject *);
 		QList<Element *> linkedElements ();
 
+		int groupIndexForElement(Element *elmt) const;
+		void setGroupIndexForElement(Element *elmt, int index);
+
 		/**
 		 * @brief linkType
 		 * use elementData function instead
@@ -228,7 +245,8 @@ class Element : public QetGraphicsItem
 	protected:
 			//ATTRIBUTES related to linked element
 		QList <Element *> connected_elements;
-		QList <QUuid>     tmp_uuids_link;
+		QList <LinkInfo>  tmp_uuids_link;
+		QHash <Element *, int> m_group_index_map;  ///< Maps linked elements to their group index (for slave->master links)
 		QUuid             m_uuid;
 		kind              m_link_type = Element::Simple;