PERF: Performance improvements to the XdmfReader (and panel) to avoid repeated

RequestInformation passes and speed up performance when reading large xmf files.

libsrc/XdmfDOM.cxx

@@ -525,6 +525,43 @@ if ( !type ) {
 return(NULL);
 }
 
+
+XdmfXmlNode  
+XdmfDOM::FindNextElement(XdmfConstString TagName, XdmfXmlNode Node, XdmfInt32 IgnoreInfo) {
+
+XdmfString type = (XdmfString )TagName;
+XdmfXmlNode child;
+
+// this->SetDebug(1);
+if(TagName){
+    XdmfDebug("FindNextElement" << TagName);
+}else{
+    XdmfDebug("FindNextElement NULL");
+}
+if(!Node) {
+    if(!this->Tree) return( NULL );
+    Node = this->Tree->children;
+}
+if(!Node) return(NULL);
+if ( type ) {
+  if( STRNCASECMP( type, "NULL", 4 ) == 0 ) type = NULL;
+}
+
+child = XdmfGetNextElement(Node);
+while (child) {
+  if(IgnoreInfo && XDMF_WORD_CMP("Information", (const char *)(child)->name)){
+    // skip Information elements.
+  } else {
+    if(!type ||
+      (XDMF_WORD_CMP((const char *)type, (const char *)(child)->name))){
+      return child;
+    }
+  }
+  child = XdmfGetNextElement(child);
+}
+return (NULL);
+}
+
 XdmfXmlNode  
 XdmfDOM::FindElementByAttribute(XdmfConstString Attribute,
     XdmfConstString Value, XdmfInt32 Index, XdmfXmlNode Node ) {

libsrc/XdmfDOM.h

@@ -181,6 +181,13 @@ the "Information" Elements not to be counted against Index.
       XdmfInt32 Index= 0,
       XdmfXmlNode Node = NULL,
       XdmfInt32 IgnoreInfo=1);
+/*!
+Find the next sibling for the node that is of a certain type. IgnoreInfo allows
+the "Information" elements to be skipped.
+*/
+  XdmfXmlNode FindNextElement(XdmfConstString TagName,
+    XdmfXmlNode Node,
+    XdmfInt32 IgnoreInfo=1);
 /*! Find DataItem, DataStructure, or DataTransform
     This is needed for backward compatibility but will
     be removed in the future and XML will be forced

libsrc/XdmfGrid.cxx

@@ -409,7 +409,12 @@ if( this->GridType & XDMF_GRID_MASK){
     }
     anElement = this->DOM->FindElement("Geometry", 0, this->Element);
     for(i=0 ; i < nchild ; i++){
-        node = this->DOM->FindElement("Grid", i, this->Element);
+        if (i==0) {
+          node = this->DOM->FindElement("Grid", i, this->Element);
+        } else {
+          node = this->DOM->FindNextElement("Grid", node);
+        }
+
         if(!node) {
             XdmfErrorMessage("Can't find Child Grid #" << i);
             return(XDMF_FAIL);
@@ -536,9 +541,12 @@ if( this->NumberOfAttributes > 0 ){
       this->NumberOfAttributes * sizeof( XdmfAttribute * ));
   for( Index = 0 ; Index < this->NumberOfAttributes ; Index++ ){
     iattribute = new XdmfAttribute;
-
     this->Attribute[Index] = iattribute;
-    AttributeElement = this->DOM->FindElement( "Attribute", Index, this->Element );
+    if (Index == 0) {
+      AttributeElement = this->DOM->FindElement( "Attribute", Index, this->Element );
+    } else {
+      AttributeElement = this->DOM->FindNextElement( "Attribute", AttributeElement);
+    }
     iattribute->SetDOM( this->DOM );    
     iattribute->SetElement( AttributeElement );
     iattribute->UpdateInformation();
@@ -562,7 +570,11 @@ if( this->NumberOfSets > 0 ){
     iSet = new XdmfSet;
 
     this->Sets[Index] = iSet;
-    SetElement = this->DOM->FindElement( "Set", Index, this->Element );
+    if (Index==0) {
+      SetElement = this->DOM->FindElement( "Set", Index, this->Element );
+    } else {
+      SetElement = this->DOM->FindNextElement( "Set", SetElement);
+    }
     iSet->SetDOM( this->DOM );    
     iSet->SetElement( SetElement );
     iSet->UpdateInformation();

vtk/vtkXdmfReader.h

@@ -58,13 +58,15 @@ public:
   int GetNumberOfDomains();
 
   // Description:
-  // Get/Set the current domain name.
-  virtual void SetDomainName(const char*);
-  vtkGetStringMacro(DomainName);
-
   // Get the name of domain at index.
   const char* GetDomainName(int idx);
 
+  // Description:
+  // Get/Set the current domain name. If none is set, the first domain will be
+  // used. 
+  virtual void SetDomainName(const char*);
+  vtkGetStringMacro(DomainName);
+
   // GRIDS ///////////////////////////////////////////////////////////////////
   // Description:
   // Get number of grids in the current domain.
@@ -90,7 +92,7 @@ public:
   void DisableGrid(const char* name);
   void DisableGrid(int idx);
   void DisableAllGrids();
-  void RemoveAllGrids();
+  void RemoveAllGrids(); // <<--FIXME: remove me.
 
   // Description:
   // Get current enable/disable of the grid
@@ -220,7 +222,13 @@ public:
 
 protected:
   vtkXdmfReader();
-  ~vtkXdmfReader();   
+  ~vtkXdmfReader();
+
+  // Description:
+  // This methods parses the XML. Returns true on success. This method can be
+  // called repeatedly. It has checks to ensure that the XML parsing is done
+  // only if needed.
+  bool ParseXML();
 
   virtual int ProcessRequest(vtkInformation *request,
                              vtkInformationVector **inputVector,