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Undo / redo edits to a PDF file using Ruby

The PDFTron SDK has a low-level facility for undo and redo operations. It is a API that applies to any edits made to a particular document (not just annotations). This sample Ruby code shows how to use PDFTron SDK to walk back and forth on a fully general, bit-exact list of document states. Saving changes in a mode that is not 'incremental' will wipe out the undo-redo state list; the API will not be able to access old snapshots anymore. See the undoing and redoing guide for more information.

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#---------------------------------------------------------------------------------------
# Copyright (c) 2001-2019 by PDFTron Systems Inc. All Rights Reserved.
# Consult LICENSE.txt regarding license information.
#---------------------------------------------------------------------------------------

require '../../../PDFNetC/Lib/PDFNetRuby'
include PDFNetRuby

$stdout.sync = true

#---------------------------------------------------------------------------------------
# The following sample illustrates how to use the UndoRedo API.
#---------------------------------------------------------------------------------------

	# The first step in every application using PDFNet is to initialize the 
	# library and set the path to common PDF resources. The library is usually 
	# initialized only once, but calling Initialize multiple times is also fine.
	PDFNet.Initialize()

	# Relative path to the folder containing test files.
	input_path = "../../TestFiles/"
	output_path = "../../TestFiles/Output/"

	# Open the PDF document.
	doc = PDFDoc.new(input_path + "newsletter.pdf")
	
	undo_manager = doc.GetUndoManager()

	# Take a snapshot to which we can undo after making changes.
	snap0 = undo_manager.TakeSnapshot()

	snap0_state = snap0.CurrentState()
	
	# Start a new page
	page = doc.PageCreate()

	builder = ElementBuilder.new()			# Used to build new Element objects
	writer = ElementWriter.new()			# Used to write Elements to the page
	writer.Begin(page)						# Begin writing to this page

	# ----------------------------------------------------------
	# Add JPEG image to the output file
	img = Image.Create(doc.GetSDFDoc(), input_path + "peppers.jpg")
	
	element = builder.CreateImage(img, Matrix2D.new(200, 0, 0, 250, 50, 500))
	writer.WritePlacedElement(element)
	
	# Finish writing to the page
	writer.End()    
	doc.PagePushFront(page)
	
	# Take a snapshot after making changes, so that we can redo later (after undoing first).
	snap1 = undo_manager.TakeSnapshot()
	
	if snap1.PreviousState().Equals(snap0_state)
		puts "snap1 previous state equals snap0_state; previous state is correct"
	end
	
	snap1_state = snap1.CurrentState()

	doc.Save(output_path + "addimage.pdf", SDFDoc::E_incremental)

	if undo_manager.CanUndo()
		undo_snap = undo_manager.Undo()

		doc.Save(output_path + "addimage_undone.pdf", SDFDoc::E_incremental)

		undo_snap_state = undo_snap.CurrentState()

		if undo_snap_state.Equals(snap0_state)
			puts "undo_snap_state equals snap0_state; undo was successful"
		end

		if undo_manager.CanRedo()
			redo_snap = undo_manager.Redo()

			doc.Save(output_path + "addimage_redone.pdf", SDFDoc::E_incremental)

			if redo_snap.PreviousState().Equals(undo_snap_state)
				puts "redo_snap previous state equals undo_snap_state; previous state is correct"
			end
			
			redo_snap_state = redo_snap.CurrentState()
			
			if redo_snap_state.Equals(snap1_state)
				puts "Snap1 and redo_snap are equal; redo was successful"
			end
		else
			puts "Problem encountered - cannot redo."
		end
	else
		puts "Problem encountered - cannot undo."
	end
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