ENH: Improve vtkMRMLLayoutNode API

The layout node did not have an API to remove a layout or easily copy all layouts.

Libs/MRML/Core/vtkMRMLLayoutNode.cxx

@@ -224,18 +224,42 @@ bool vtkMRMLLayoutNode::SetLayoutDescription(int layout, const char* layoutDescr
     vtkDebugMacro( << "Layout " << layout << " has NOT been registered");
     return false;
   }
-  if (this->Layouts[layout] == layoutDescription)
+  std::string layoutDescriptionStr;
+  if (layoutDescription)
   {
+    layoutDescriptionStr = std::string(layoutDescription);
+  }
+  if (this->Layouts[layout] == layoutDescriptionStr)
+  {
+    // No change
     return true;
   }
-  this->Layouts[layout] = std::string(layoutDescription);
+  if (layoutDescriptionStr.empty())
+  {
+    this->Layouts.erase(layout);
+  }
+  else
+  {
+    this->Layouts[layout] = layoutDescriptionStr;
+  }
   int wasModifying = this->StartModify();
   this->UpdateCurrentLayoutDescription();
   this->Modified();
   this->EndModify(wasModifying);
   return true;
 }
 
+//----------------------------------------------------------------------------
+std::vector<int> vtkMRMLLayoutNode::GetLayoutIndices()
+{
+  std::vector<int> indices;
+  for (const auto& keyValuePair : this->Layouts)
+  {
+    indices.push_back(keyValuePair.first);
+  }
+  return indices;
+}
+
 //----------------------------------------------------------------------------
 bool vtkMRMLLayoutNode::IsLayoutDescription(int layout)
 {
@@ -357,6 +381,18 @@ void vtkMRMLLayoutNode::Copy(vtkMRMLNode *anode)
   this->EndModify(disabledModify);
 }
 
+//----------------------------------------------------------------------------
+void vtkMRMLLayoutNode::CopyLayoutDescriptions(vtkMRMLLayoutNode* source)
+{
+  if (!source)
+  {
+    vtkErrorMacro("CopyLayoutDescriptions: Invalid source node");
+    return;
+  }
+  this->Layouts = source->Layouts;
+  this->Modified();
+}
+
 //----------------------------------------------------------------------------
 void vtkMRMLLayoutNode::PrintSelf(ostream& os, vtkIndent indent)
 {

Libs/MRML/Core/vtkMRMLLayoutNode.h

@@ -139,15 +139,23 @@ class VTK_MRML_EXPORT vtkMRMLLayoutNode : public vtkMRMLAbstractLayoutNode
   /// Modifies a layout description for integer identifier
   /// "layout". Returns false without making any modifications if the
   /// integer identifier "layout" has NOT already been added.
+  /// If layoutDescription is empty then the layout is removed.
   bool SetLayoutDescription(int layout, const char* layoutDescription);
 
+  /// Get list of all specified layout indices
+  std::vector<int> GetLayoutIndices();
+
   /// Query whether a layout exists with a specified integer identifier
   bool IsLayoutDescription(int layout);
 
   /// Get the layout description associated with a specified integer
   /// identifier. The empty string is returned if the layout does not exist.
   std::string GetLayoutDescription(int layout);
 
+  /// Copy all layout descriptions from the specified layout node.
+  /// All the previous layout descriptions are replaced.
+  void CopyLayoutDescriptions(vtkMRMLLayoutNode* source);
+
   // Get the layout description currently displayed. Used
   // internally. This is XML description corresponding to the ivar
   // ViewArrangement which is the integer identifier for the