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PDF layers (OCG) in PHP

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Sample PHP 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 PHP PDF Library.

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// Copyright (c) 2001-2020 by PDFTron Systems Inc. All Rights Reserved.
// Consult LICENSE.txt regarding license information.

// Relative path to the folder containing test files.
$input_path = getcwd()."/../../TestFiles/";
$output_path = $input_path."Output/";

// This sample demonstrates how to create layers in PDF.
// The sample also shows how to extract and render PDF layers in documents 
// that contain optional content groups (OCGs)
// With the introduction of PDF version 1.5 came the concept of Layers. 
// Layers, or as they are more formally known Optional Content Groups (OCGs),
// refer to sections of content in a PDF document that can be selectively 
// viewed or hidden by document authors or consumers. This capability is useful 
// in CAD drawings, layered artwork, maps, multi-language documents etc.
// Notes: 
// ---------------------------------------
// - This sample is using CreateLayer() utility method to create new OCGs. 
//   CreateLayer() is relatively basic, however it can be extended to set 
//   other optional entries in the 'OCG' and 'OCProperties' dictionary. For 
//   a complete listing of possible entries in OC dictionary please refer to 
//   section 4.10 'Optional Content' in the PDF Reference Manual.
// - The sample is grouping all layer content into separate Form XObjects. 
//   Although using PDFNet is is also possible to specify Optional Content in 
//   Content Streams (Section 4.10.2 in PDF Reference), Optional Content in  
//   XObjects results in PDFs that are cleaner, less-error prone, and faster 
//   to process.

// A utility function used to add new Content Groups (Layers) to the document.
function CreateLayer($doc, $layer_name)
	$grp = Group::Create($doc, $layer_name);
	$cfg = $doc->GetOCGConfig();
	if (!$cfg->IsValid()) {
		$cfg = Config::Create($doc, true);

	// Add the new OCG to the list of layers that should appear in PDF viewer GUI.
	$layer_order_array = $cfg->GetOrder();
	if (!$layer_order_array) {
        	$layer_order_array = $doc->CreateIndirectArray();

	return $grp;

// Creates some content (3 images) and associate them with the image layer
function CreateGroup1($doc, $layer) 
	$writer = new ElementWriter();
	global $input_path;
	// Create an Image that can be reused in the document or on the same page.		
	$img = Image::Create($doc->GetSDFDoc(), $input_path."peppers.jpg");

	$builder = new ElementBuilder();
	$element = $builder->CreateImage($img, new Matrix2D((double)$img->GetImageWidth()/2, -145.0, 20.0, 
							(double)$img->GetImageHeight()/2, 200.0, 150.0));

	$gstate = $element->GetGState();	// use the same image (just change its matrix)
	$gstate->SetTransform(200.0, 0.0, 0.0, 300.0, 50.0, 450.0);

	// use the same image again (just change its matrix).
	$writer->WritePlacedElement($builder->CreateImage($img, 300.0, 600.0, 200.0, -150.0));

	$grp_obj = $writer->End();	

	// Indicate that this form (content group) belongs to the given layer (OCG).
	$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 content (a path in the shape of a heart) and associate it with the vector layer
function CreateGroup2($doc, $layer) 
	$writer = new ElementWriter();

	// Create a path object in the shape of a heart.
	$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);
	$element = $builder->PathEnd(); // the path geometry is now specified.

	// Set the path FILL color space and color.
	$gstate = $element->GetGState();
	$gstate->SetFillColor(new ColorPt(1.0, 0.0, 0.0, 0.0));  // cyan

	// Set the path STROKE color space and color.
	$gstate->SetStrokeColor(new ColorPt(1.0, 0.0, 0.0));  // red

	$gstate->SetTransform(0.5, 0.0, 0.0, 0.5, 280.0, 300.0);


	$grp_obj = $writer->End();	

	// Indicate that this form (content group) belongs to the given layer (OCG).
	$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
function CreateGroup3($doc, $layer) 
	$writer = new ElementWriter();

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

	// Begin writing a block of text
	$element = $builder->CreateTextBegin(Font::Create($doc->GetSDFDoc(), Font::e_times_roman), 120.0);

	$element = $builder->CreateTextRun("A text layer!");

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


	$grp_obj = $writer->End();	

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

	return $grp_obj;

	PDFNet::GetSystemFontList();    // Wait for fonts to be loaded if they haven't already. This is done because PHP can run into errors when shutting down if font loading is still in progress.

	$doc = new PDFDoc();

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

	// Start a new page ------------------------------------
	$page = $doc->PageCreate();

	$builder = new ElementBuilder();	// ElementBuilder is used to build new Element objects
	$writer = new ElementWriter;	// ElementWriter is used to write Elements to the page	
	$writer->Begin($page);		// Begin writing to the page

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

	$element = $builder->CreateForm(CreateGroup2($doc, $vector_layer->GetSDFObj()));

	// Add the text layer to the page...
	if (false)  // set to true to enable 'ocmd' example.
		// 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.
		$ocgs = $doc->CreateIndirectArray();
		$text_ocmd = OCMD::Create($doc, $ocgs, OCMD::e_AllOn);
		$element = $builde->CreateForm(CreateGroup3($doc, $text_ocmd->GetSDFObj()));
	else {
		$element = $builder->CreateForm(CreateGroup3($doc, $text_layer->GetSDFObj()));


	// 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());

	$writer->End();  // save changes to the current page

	// Set the default viewing preference to display 'Layer' tab.
	$prefs = $doc->GetViewPrefs();

	$doc->Save($output_path."pdf_layers.pdf", SDFDoc::e_linearized);
	echo nl2br("Done.\n");

	// The following is a code snippet shows how to selectively render 
	// and export PDF layers.
	$doc = new PDFDoc($output_path."pdf_layers.pdf");

	if (!$doc->HasOC()) {
		echo nl2br("The document does not contain 'Optional Content'\n");
	else {
		$init_cfg = $doc->GetOCGConfig();
		$ctx = new Context($init_cfg);

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

		$page = $doc->GetPage(1); // Get the first page in the document.
		$pdfdraw->Export($page, $output_path."pdf_layers_default.png");

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

		// Now render each layer in the input document to a separate image.
		$ocgs = $doc->GetOCGs(); // Get the array of all OCGs in the document.
		if ($ocgs != null) {
			$sz = $ocgs->Size();
			for ($i=0; $i<$sz; ++$i) {
				$ocg = new Group($ocgs->GetAt($i));
				$ctx->SetState($ocg, true);
				$fname = $output_path."pdf_layers_".$ocg->GetName().".png";
				echo nl2br($fname."\n");
				$pdfdraw->Export($page, $fname);

		// Now draw content that is not part of any layer...
		$pdfdraw->Export($page, $output_path."pdf_layers_non_oc.png");

	echo nl2br("Done.\n");	

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