feat: implement MultiSelectionProp to support grouped object transformation and selection in Viewport

src/Vtk/vtkViewport.h

@@ -29,6 +29,7 @@ namespace Vtk {
 
 struct ViewportData;
 class HandlerWidget;
+class MultiSelectionProp;
 class ObjectsContext;
 
 /**
@@ -49,7 +50,11 @@ public:
     // Prop3D / prop management
     void AddProp3D(Prop3D &prop);
     void RemoveProp3D(Prop3D &prop);
-    void SelectProp3D(Prop3D *prop);
+    /** @brief Selects a specific Prop3D. If multi is true, it toggles selection in a group. */
+    void SelectProp3D(Prop3D* target, bool multi = false);
+
+    /** @brief Creates a persistent Selection Group from the current multi-selection. */
+    void GroupSelection(uLib::ObjectsContext* targetCtx);
     void addProp(vtkProp *prop);
     void RemoveProp(vtkProp *prop);
 
@@ -91,6 +96,8 @@ protected:
     struct ViewportData *pv;
     Axis                                         m_GridAxis;
     std::vector<Prop3D*>                         m_Prop3Ds;
+    std::vector<Prop3D*>                         m_SelectedProps;
+    MultiSelectionProp*                          m_MultiSelectionProp;
     std::map<uLib::Object*, Prop3D*>             m_ObjectToProp3D;
 };