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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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//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2023 by Apryse Software Inc. All Rights Reserved.
// Consult legal.txt regarding legal and license information.
//---------------------------------------------------------------------------------------
#include <SDF/Obj.h>
#include <PDF/PDFNet.h>
#include <PDF/PDFDoc.h>
#include <PDF/PDFDraw.h>
#include <PDF/OCG/OCMD.h>
#include <PDF/ElementBuilder.h>
#include <PDF/ElementWriter.h>
#include <PDF/ElementReader.h>
#include <iostream>
#include "../../LicenseKey/CPP/LicenseKey.h"
using namespace pdftron;
using namespace Common;
using namespace SDF;
using namespace PDF;
using namespace std;
//-----------------------------------------------------------------------------------
// 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.
//-----------------------------------------------------------------------------------
Obj CreateGroup1(PDFDoc& doc, Obj layer);
Obj CreateGroup2(PDFDoc& doc, Obj layer);
Obj CreateGroup3(PDFDoc& doc, Obj layer);
OCG::Group CreateLayer(PDFDoc& doc, const char* layer_name);
// Relative path to the folder containing test files.
static const string input_path = "../../TestFiles/";
static const string output_path = "../../TestFiles/Output/";
int main(int argc, char *argv[])
{
int ret = 0;
PDFNet::Initialize(LicenseKey);
try
{
PDFDoc doc;
// Create three layers...
OCG::Group image_layer = CreateLayer(doc, "Image Layer");
OCG::Group text_layer = CreateLayer(doc, "Text Layer");
OCG::Group vector_layer = CreateLayer(doc, "Vector Layer");
// Start a new page ------------------------------------
Page page = doc.PageCreate();
ElementBuilder builder; // ElementBuilder is used to build new Element objects
ElementWriter writer; // 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 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...
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.
Obj ocgs = doc.CreateIndirectArray();
ocgs.PushBack(image_layer.GetSDFObj());
ocgs.PushBack(vector_layer.GetSDFObj());
ocgs.PushBack(text_layer.GetSDFObj());
OCG::OCMD text_ocmd = OCG::OCMD::Create(doc, ocgs, OCG::OCMD::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(PDFDocViewPrefs::e_UseOC);
doc.Save((output_path + "pdf_layers.pdf").c_str(), SDFDoc::e_linearized, 0);
cout << "Done." << endl;
}
catch(Common::Exception& e)
{
cout << e << endl;
ret = 1;
}
catch(...)
{
cout << "Unknown Exception" << endl;
ret = 1;
}
// The following is a code snippet shows how to selectively render
// and export PDF layers.
try
{
PDFDoc doc((output_path + "pdf_layers.pdf").c_str());
doc.InitSecurityHandler();
if (!doc.HasOC()) {
cout << "The document does not contain 'Optional Content'" << endl;
}
else {
OCG::Config init_cfg = doc.GetOCGConfig();
OCG::Context ctx(init_cfg);
PDFDraw pdfdraw;
pdfdraw.SetImageSize(1000, 1000);
pdfdraw.SetOCGContext(&ctx); // Render the page using the given OCG context.
Page page = doc.GetPage(1); // Get the first page in the document.
pdfdraw.Export(page, (output_path + "pdf_layers_default.png").c_str());
// 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 != 0) {
int i, sz = int(ocgs.Size());
for (i=0; i<sz; ++i) {
OCG::Group ocg(ocgs.GetAt(i));
ctx.ResetStates(false);
ctx.SetState(ocg, true);
std::string fname("pdf_layers_");
fname += ocg.GetName().ConvertToAscii();
fname += ".png";
cout << fname << endl;
pdfdraw.Export(page, (output_path + fname).c_str());
}
}
// Now draw content that is not part of any layer...
ctx.SetNonOCDrawing(true);
ctx.SetOCDrawMode(OCG::Context::e_NoOC);
pdfdraw.Export(page, (output_path + "pdf_layers_non_oc.png").c_str());
}
cout << "Done." << endl;
}
catch(Common::Exception& e)
{
cout << e << endl;
ret = 1;
}
catch(...)
{
cout << "Unknown Exception" << endl;
ret = 1;
}
PDFNet::Terminate();
return ret;
}
// A utility function used to add new Content Groups (Layers) to the document.
OCG::Group CreateLayer(PDFDoc& doc, const char* layer_name)
{
OCG::Group grp = OCG::Group::Create(doc, layer_name);
OCG::Config cfg = doc.GetOCGConfig();
if (!cfg.IsValid()) {
cfg = OCG::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) {
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;
writer.Begin(doc);
// Create an Image that can be reused in the document or on the same page.
Image img = Image::Create(doc, (input_path + "peppers.jpg").c_str());
ElementBuilder builder;
Element element = builder.CreateImage(img, Common::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.
return grp_obj;
}
// Creates some content (a path in the shape of a heart) and associate it with the vector layer
Obj CreateGroup2(PDFDoc& doc, Obj layer)
{
ElementWriter writer;
writer.Begin(doc);
// Create a path object in the shape of a heart.
ElementBuilder builder;
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(ColorPt(1, 0, 0, 0)); // cyan
// Set the path STROKE color space and color.
element.SetPathStroke(true);
gstate.SetStrokeColorSpace(ColorSpace::CreateDeviceRGB());
gstate.SetStrokeColor(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
Obj CreateGroup3(PDFDoc& doc, Obj layer)
{
ElementWriter writer;
writer.Begin(doc);
// Create a path object in the shape of a heart.
ElementBuilder builder;
// Begin writing a block of text
Element element = builder.CreateTextBegin(Font::Create(doc, Font::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 *= Matrix2D(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;
}