From bdfe5fd14f9be4c75b54f90247595d93a9f499ea Mon Sep 17 00:00:00 2001
From: Andras Lasso <lasso@queensu.ca>
Date: Wed, 9 Oct 2013 18:31:29 -0400
Subject: [PATCH] ENH: Don't batch process when show/hide only a few child
 nodes

When there are many child nodes in a hierarchy then show/hide is much more efficient if batch processing is enabled.
However, if there are few nodes only then a full refresh at the end of a batch processing takes longer than doing the update on each node separately.
Count the number of child nodes and if there are less than 30 then update each node separately.
---
 Libs/MRML/Widgets/qMRMLTreeView.cxx | 51 +++++++++++++++++++++++++++--
 Libs/MRML/Widgets/qMRMLTreeView_p.h |  6 ++++
 2 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/Libs/MRML/Widgets/qMRMLTreeView.cxx b/Libs/MRML/Widgets/qMRMLTreeView.cxx
index 2adb1b5e2..638c97657 100644
--- a/Libs/MRML/Widgets/qMRMLTreeView.cxx
+++ b/Libs/MRML/Widgets/qMRMLTreeView.cxx
@@ -18,6 +18,13 @@
 
 ==============================================================================*/
 
+// If the number of child nodes is more than this number then show/hide operations
+// are performed in batch processing mode.
+static const int BATCH_VISIBILITY_UPDATE_THRESHOLD=30;
+
+// STL includes
+#include <deque>
+
 // Qt includes
 #include <QDebug>
 #include <QHeaderView>
@@ -289,6 +296,39 @@ void qMRMLTreeViewPrivate::scrollTo(const QString& name, bool next)
     modelIndex, QItemSelectionModel::Current);
 }
 
+//-----------------------------------------------------------------------------
+bool qMRMLTreeViewPrivate::ManyChildrenNodes(vtkMRMLHierarchyNode* rootNode, int manyThreshold)
+{
+  int totalChildrenCount=0;
+  std::deque<vtkMRMLHierarchyNode*> parentNodesToProcess;
+  parentNodesToProcess.push_back(rootNode);
+  while (!parentNodesToProcess.empty())
+  {
+    vtkMRMLHierarchyNode* parent=parentNodesToProcess.front();
+    if (parent==NULL)
+    {
+      continue;
+    }
+
+    int childrenCount=parent->GetNumberOfChildrenNodes();
+    totalChildrenCount+=childrenCount;
+    if (totalChildrenCount>manyThreshold)
+    {
+      return true;
+    }
+    for ( int i = 0; i < childrenCount; ++i)
+    {
+      vtkMRMLHierarchyNode* child = parent->GetNthChildNode(i);
+      if (child && child->GetNumberOfChildrenNodes()>0)
+      {
+        parentNodesToProcess.push_back(child);
+      }
+    }
+    parentNodesToProcess.pop_front();
+  }
+  return false;
+}
+
 //------------------------------------------------------------------------------
 // qMRMLTreeView
 //------------------------------------------------------------------------------
@@ -848,9 +888,16 @@ void qMRMLTreeView::toggleVisibility(const QModelIndex& index)
       {
       visibility = (hierDisplayNode->GetVisibility() ? 0 : 1);
       }
-    this->mrmlScene()->StartState(vtkMRMLScene::BatchProcessState);
+    bool batchProcess=qMRMLTreeViewPrivate::ManyChildrenNodes(displayableHierarchyNode,BATCH_VISIBILITY_UPDATE_THRESHOLD);
+    if (batchProcess)
+      {
+      this->mrmlScene()->StartState(vtkMRMLScene::BatchProcessState);
+      }
     vtkMRMLModelHierarchyLogic::SetChildrenVisibility(displayableHierarchyNode,visibility);
-    this->mrmlScene()->EndState(vtkMRMLScene::BatchProcessState);
+    if (batchProcess)
+      {
+      this->mrmlScene()->EndState(vtkMRMLScene::BatchProcessState);
+      }
     }
   else if (displayNode)
     {
diff --git a/Libs/MRML/Widgets/qMRMLTreeView_p.h b/Libs/MRML/Widgets/qMRMLTreeView_p.h
index 741e467d0..2b790178b 100644
--- a/Libs/MRML/Widgets/qMRMLTreeView_p.h
+++ b/Libs/MRML/Widgets/qMRMLTreeView_p.h
@@ -25,6 +25,9 @@
 class QAction;
 class QMenu;
 
+// MRML includes
+class vtkMRMLHierarchyNode;
+
 // MRMLWidgets includes
 #include "qMRMLTreeView.h"
 class qMRMLSceneModel;
@@ -52,6 +55,9 @@ public:
   void saveChildrenExpandState(QModelIndex& parentIndex);
   void scrollTo(const QString& name, bool next);
 
+  /// Returns true if the hierarchy node has mode children (and descendant) nodes than manyThreshold
+  static bool ManyChildrenNodes(vtkMRMLHierarchyNode* rootNode, int manyThreshold);
+
   qMRMLSceneModel*           SceneModel;
   qMRMLSortFilterProxyModel* SortFilterModel;
   QString                    SceneModelType;
-- 
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