I have a Virtual Treeview with multiline nodes. However when the text in the nodes gets bigger the scrolling of the tree gets intolerably slow. A quick look into a simple "one node with large text" application with sampling profiler shows that most of the time is spent in gdi32.dll.

I have a Virtual Treeview with multiline nodes. However when the text in the nodes gets bigger the scrolling of the tree gets intolerably slow. A quick look into a simple "one node with large text" application with sampling profiler shows that most of the time is spent in gdi32.dll.

So I guess somehow the painting code has an issue with the large text. Anyone know a solution?

Here is the code required to reproduce the problem:

procedure TForm1.FormCreate(Sender: TObject);
begin
  VirtualStringTree1.TreeOptions.MiscOptions :=
    VirtualStringTree1.TreeOptions.MiscOptions + [toVariableNodeHeight];
  VirtualStringTree1.RootNodeCount := 1;
end;

procedure TForm1.VirtualStringTree1GetText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
  var CellText: string);
begin
  CellText := s; // >20000 characters and the problem becomes visible
end;

procedure TForm1.VirtualStringTree1InitNode(Sender: TBaseVirtualTree;
  ParentNode, Node: PVirtualNode; var InitialStates: TVirtualNodeInitStates);
begin
  Sender.MultiLine[Node] := True;
end;

procedure TForm1.VirtualStringTree1MeasureItem(Sender: TBaseVirtualTree;
  TargetCanvas: TCanvas; Node: PVirtualNode; var NodeHeight: Integer);
begin
  NodeHeight := 1500;
end;