DynaPDF Manual - Page 469

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Function Reference

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// This algorithm is a bit simplified. In a real world application we must store the OCG handles in

// the tree node so that the layer state can be changed. The Delphi tree control supports the user

// defined pointer Data which can be used for this purpose. However, Data is a pointer and therefore

// we must store the OCG handles in a list before we can set the pointer. In addition, a standard

// tree control does not support the features we need to show or hide layers.

// We assume that the PDF file was already opened.

procedure TForm1.LoadLayerTreeNodes(Parent: TTreeNode; Next: IOCN; Level: Integer);

var node: TOCUINode; ocg: TPDFOCG; lbl: String; prnt, saved: TTreeNode;

begin

if Level > 32 then Exit; // A maximum recursion depth of 32 should be more than enough.

node.StructSize := sizeof(node);

ocg.StructSize

:= sizeof(ocg);

saved := Parent;

while Next <> nil do begin

node.NextChild := nil;

node.OCG

:= -1;

Next

:= FPDF.GetOCUINode(Next, @node);

if node.OCG < 0 then begin

lbl := GetString(node.LabelA, node.LabelW);

if node.NewNode then

prnt := LayerTree.Items.AddNode(nil, Parent, lbl, nil, naAddChild)

else

prnt := Parent;

LoadLayerTreeNodes(prnt, node.NextChild, Level +1);

Parent := saved; // Important! Restore the parent tree node.

end else begin

if FPDF.GetOCG(node.OCG, ocg) then begin

lbl := GetString(ocg.NameA, ocg.NameW);

if node.NewNode then begin

saved

:= Parent; // Important! Save the parent tree node.

Parent := LayerTree.Items.AddNode(nil, Parent, lbl, nil, naAddChild)

end else

LayerTree.Items.AddNode(nil, Parent, lbl, nil, naAddChild);

end;

end;

end;

end;

procedure TForm1.LoadLayerTree;

var next: IOCN;

begin

FPDF.ImportOCProperties;

// Import the global Optional Content Properties

FPDF.LoadLayerConfig(-1);

// Load the default layer configuration

next := FPDF.GetOCUINode(nil, nil);

// Get the root node

LoadLayerTreeNodes(nil, next, 0);

// Load the children of the root

end;

Although the syntax is slightly different among different programming languages, the general

algorithm stays the same.

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