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PDF layers (OCG) in C#

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Sample C# code to use PDFTron SDK for creating and manipulating PDF layers (also known as Optional Content Groups - OCGs). These samples demonstrate how to create and extract layers, as well as to selectively render them (show, hide) in conforming PDF readers or printers. Learn more about our C# PDF Library.

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using System;
using System.IO;
using System.Threading.Tasks;
using Windows.Foundation;

using pdftron.Common;
using pdftron.PDF;
using pdftron.PDF.OCG;
using pdftron.SDF;

using PDFNetUniversalSamples.ViewModels;

namespace PDFNetSamples
{
    public sealed class PDFLayersTest : Sample
    {
        public PDFLayersTest() :
            base("PDFLayers", "This sample demonstrates how to create PDF layers (also known as Optional Content Groups - OCGs). The sample also shows how to extract and render PDF layers.")
        {
        }

        public override IAsyncAction RunAsync()
        {
            return Task.Run(new System.Action(async () => {
                WriteLine("--------------------------------");
                WriteLine("Starting PDFLayers Test...");
                WriteLine("--------------------------------\n");
			    try
			    {
				    PDFDoc doc = new PDFDoc();

				    // Create three layers...
				    Group image_layer = CreateLayer(doc, "Image Layer");
				    Group text_layer = CreateLayer(doc, "Text Layer");
				    Group vector_layer = CreateLayer(doc, "Vector Layer");

				    // Start a new page ------------------------------------
				    pdftron.PDF.Page page = doc.PageCreate();

				    ElementBuilder builder = new ElementBuilder(); // ElementBuilder is used to build new Element objects
				    ElementWriter writer = new ElementWriter(); // ElementWriter is used to write Elements to the page
				    writer.Begin(page);	// begin writing to this page

				    // Add new content to the page and associate it with one of the layers.
				    Element element = builder.CreateForm(CreateGroup1(doc, image_layer.GetSDFObj()));
				    writer.WriteElement(element);

				    element = builder.CreateForm(CreateGroup2(doc, vector_layer.GetSDFObj()));
				    writer.WriteElement(element);

				    // Add the text layer to the page...
                    bool ocmdSample = false;  // set to 'true' to enable 'ocmd' example.
                    if (ocmdSample)
				    {
					    // A bit more advanced example of how to create an OCMD text layer that 
					    // is visible only if text, image and path layers are all 'ON'.
					    // An example of how to set 'Visibility Policy' in OCMD.
					    Obj ocgs = doc.CreateIndirectArray();
					    ocgs.PushBack(image_layer.GetSDFObj());
					    ocgs.PushBack(vector_layer.GetSDFObj());
					    ocgs.PushBack(text_layer.GetSDFObj());
					    OCMD text_ocmd = OCMD.Create(doc, ocgs, OCMDVisibilityPolicyType.e_AllOn);
					    element = builder.CreateForm(CreateGroup3(doc, text_ocmd.GetSDFObj()));
				    }
				    else {
					    element = builder.CreateForm(CreateGroup3(doc, text_layer.GetSDFObj()));
				    }
				    writer.WriteElement(element);

				    // Add some content to the page that does not belong to any layer...
				    // In this case this is a rectangle representing the page border.
				    element = builder.CreateRect(0, 0, page.GetPageWidth(), page.GetPageHeight());
				    element.SetPathFill(false);
				    element.SetPathStroke(true);
				    element.GetGState().SetLineWidth(40);
				    writer.WriteElement(element);

                    writer.End();  // save changes to the current page
				    doc.PagePushBack(page);

				    // Set the default viewing preference to display 'Layer' tab.
				    PDFDocViewPrefs prefs = doc.GetViewPrefs();
				    prefs.SetPageMode(PDFDocViewPrefsPageMode.e_UseOC);

                    string output_file_path = Path.Combine(OutputPath, "pdf_layers.pdf");
                    await doc.SaveAsync(output_file_path, SDFDocSaveOptions.e_linearized);
				    doc.Destroy();
                    WriteLine("Done. Results saved in " + output_file_path);
                    await AddFileToOutputList(output_file_path).ConfigureAwait(false);
			    }
			    catch (Exception e)
			    {
                    WriteLine(GetExceptionMessage(e));
			    }

			    // The following is a code snippet shows how to selectively render 
			    // and export PDF layers.
			    try  
			    {	 
				    PDFDoc doc = new PDFDoc(Path.Combine(OutputPath, "pdf_layers.pdf"));
				    doc.InitSecurityHandler();

				    if (!doc.HasOC()) 
				    {
					    WriteLine("The document does not contain 'Optional Content'");
				    }
				    else 
				    {
					    Config init_cfg = doc.GetOCGConfig();
					    Context ctx = new Context(init_cfg);

					    PDFDraw pdfdraw = new PDFDraw();
					    pdfdraw.SetImageSize(1000, 1000);
					    pdfdraw.SetOCGContext(ctx); // Render the page using the given OCG context.

					    pdftron.PDF.Page page = doc.GetPage(1); // Get the first page in the document.
                        string output_file_path = Path.Combine(OutputPath, "pdf_layers_default.png");
                        pdfdraw.Export(page, output_file_path);
                        WriteLine("Exporting " + output_file_path);
                        await AddFileToOutputList(output_file_path).ConfigureAwait(false);

					    // Disable drawing of content that is not optional (i.e. is not part of any layer).
					    ctx.SetNonOCDrawing(false);

					    // Now render each layer in the input document to a separate image.
					    Obj ocgs = doc.GetOCGs(); // Get the array of all OCGs in the document.
					    if (ocgs != null) 
					    {
						    int i, sz = ocgs.Size();
						    for (i=0; i<sz; ++i) 
						    {
							    Group ocg = new Group(ocgs.GetAt(i));
							    ctx.ResetStates(false);
							    ctx.SetState(ocg, true);
							    string fname = Path.Combine(OutputPath, "pdf_layers_" + ocg.GetName() + ".png");
							    WriteLine(fname);
							    pdfdraw.Export(page, fname);
                                WriteLine("Exporting " + fname);
                                await AddFileToOutputList(fname).ConfigureAwait(false);
						    }
					    }

					    // Now draw content that is not part of any layer...
					    ctx.SetNonOCDrawing(true);
					    ctx.SetOCDrawMode(ContextOCDrawMode.e_NoOC);
                        output_file_path =  Path.Combine(OutputPath, "pdf_layers_non_oc.png");
                        pdfdraw.Export(page, output_file_path);
                        WriteLine("Exporting " + output_file_path);
                        await AddFileToOutputList(output_file_path).ConfigureAwait(false);

					    doc.Destroy();
                        WriteLine("Done.");
				    }
			    }
			    catch (Exception e)
			    {
                    WriteLine(GetExceptionMessage(e));
                }

                WriteLine("\n--------------------------------");
                WriteLine("Done PDFLayers Test.");
                WriteLine("--------------------------------\n");
            })).AsAsyncAction();
		}

		// A utility function used to add new Content Groups (Layers) to the document.
        Group CreateLayer(PDFDoc doc, String layer_name)
		{
			Group grp = Group.Create(doc, layer_name);
			Config cfg = doc.GetOCGConfig();
			if (cfg == null) 
			{
				cfg = Config.Create(doc, true);
				cfg.SetName("Default");
			}

			// Add the new OCG to the list of layers that should appear in PDF viewer GUI.
			Obj layer_order_array = cfg.GetOrder();
			if (layer_order_array == null) 
			{
				layer_order_array = doc.CreateIndirectArray();
				cfg.SetOrder(layer_order_array);
			}
			layer_order_array.PushBack(grp.GetSDFObj());

			return grp;
		}

		// Creates some content (3 images) and associate them with the image layer
        Obj CreateGroup1(PDFDoc doc, Obj layer)
		{
			ElementWriter writer = new ElementWriter();
            writer.Begin(doc.GetSDFDoc());

			// Create an Image that can be reused in the document or on the same page.		
			pdftron.PDF.Image img = pdftron.PDF.Image.Create(doc.GetSDFDoc(), Path.Combine(InputPath, "peppers.jpg"));

			ElementBuilder builder = new ElementBuilder();
			Element element = builder.CreateImage(img, new Matrix2D(img.GetImageWidth()/2, -145, 20, img.GetImageHeight()/2, 200, 150));
			writer.WritePlacedElement(element);

			GState gstate = element.GetGState();	// use the same image (just change its matrix)
			gstate.SetTransform(200, 0, 0, 300, 50, 450);
			writer.WritePlacedElement(element);

			// use the same image again (just change its matrix).
			writer.WritePlacedElement(builder.CreateImage(img, 300, 600, 200, -150));

			Obj grp_obj = writer.End();	

			// Indicate that this form (content group) belongs to the given layer (OCG).
			grp_obj.PutName("Subtype","Form");
			grp_obj.Put("OC", layer);	
			grp_obj.PutRect("BBox", 0, 0, 1000, 1000);  // Set the clip box for the content.
            
			// As an example of further configuration, set the image layer to
			// be visible on screen, but not visible when printed...

			// The AS entry is an auto state array consisting of one or more usage application 
			// dictionaries that specify how conforming readers shall automatically set the 
			// state of optional content groups based on external factors.
			Obj cfg = doc.GetOCGConfig().GetSDFObj();
			Obj auto_state = cfg.FindObj("AS");
			if (auto_state == null) auto_state = cfg.PutArray("AS");
			Obj print_state = auto_state.PushBackDict();
			print_state.PutArray("Category").PushBackName("Print");
			print_state.PutName("Event", "Print");
			print_state.PutArray("OCGs").PushBack(layer);

			Obj layer_usage = layer.PutDict("Usage");

			Obj view_setting = layer_usage.PutDict("View");
			view_setting.PutName("ViewState", "ON");

			Obj print_setting = layer_usage.PutDict("Print");
			print_setting.PutName("PrintState", "OFF");

            return grp_obj;
		}

		// Creates some content (a path in the shape of a heart) and associate it with the vector layer
        static public Obj CreateGroup2(PDFDoc doc, Obj layer)
		{
			ElementWriter writer = new ElementWriter();
            writer.Begin(doc.GetSDFDoc());

			// Create a path object in the shape of a heart.
			ElementBuilder builder = new ElementBuilder();
			builder.PathBegin();		// start constructing the path
			builder.MoveTo(306, 396);
			builder.CurveTo(681, 771, 399.75, 864.75, 306, 771);
			builder.CurveTo(212.25, 864.75, -69, 771, 306, 396);
			builder.ClosePath();
			Element element = builder.PathEnd(); // the path geometry is now specified.

			// Set the path FILL color space and color.
			element.SetPathFill(true);
			GState gstate = element.GetGState();
			gstate.SetFillColorSpace(ColorSpace.CreateDeviceCMYK()); 
			gstate.SetFillColor(new ColorPt(1, 0, 0, 0));  // cyan

			// Set the path STROKE color space and color.
			element.SetPathStroke(true); 
			gstate.SetStrokeColorSpace(ColorSpace.CreateDeviceRGB()); 
			gstate.SetStrokeColor(new ColorPt(1, 0, 0));  // red
			gstate.SetLineWidth(20);

			gstate.SetTransform(0.5, 0, 0, 0.5, 280, 300);

			writer.WriteElement(element);

            Obj grp_obj = writer.End();	

			// Indicate that this form (content group) belongs to the given layer (OCG).
			grp_obj.PutName("Subtype","Form");
			grp_obj.Put("OC", layer);
			grp_obj.PutRect("BBox", 0, 0, 1000, 1000); 	// Set the clip box for the content.

			return grp_obj;
		}

		// Creates some text and associate it with the text layer
        static public Obj CreateGroup3(PDFDoc doc, Obj layer)
		{
			ElementWriter writer = new ElementWriter();
            writer.Begin(doc.GetSDFDoc());

			// Create a path object in the shape of a heart.
			ElementBuilder builder = new ElementBuilder();

			// Begin writing a block of text
			Element element = builder.CreateTextBegin(Font.Create(doc.GetSDFDoc(), FontStandardType1Font.e_times_roman), 120);
			writer.WriteElement(element);

			element = builder.CreateTextRun("A text layer!");

			// Rotate text 45 degrees, than translate 180 pts horizontally and 100 pts vertically.
			Matrix2D transform = Matrix2D.RotationMatrix(-45 *  (3.1415/ 180.0));
			transform.Concat(1, 0, 0, 1, 180, 100);  
			element.SetTextMatrix(transform);

			writer.WriteElement(element);
			writer.WriteElement(builder.CreateTextEnd());

            Obj grp_obj = writer.End();	

			// Indicate that this form (content group) belongs to the given layer (OCG).
			grp_obj.PutName("Subtype","Form");
			grp_obj.Put("OC", layer);
			grp_obj.PutRect("BBox", 0, 0, 1000, 1000); 	// Set the clip box for the content.

			return grp_obj;
		}
	}
}
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