Question

I mean using a c or c++ lib. to manipullate. former I use cairo lib, successfully create the pdf file, but no layers. now I want to create pdf file with several layers.

thanks

Answer 1

You can create (also read and edit) PDF layers (also know an Optional Content Groups) as shown in PDFLayers sample which is also included as part of PDFNet SDK.

The following is a relevant code:

    PDFNet.Initialize();
    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("my.pdf", SDFDoc::e_linearized, 0);

Note: I am a PDFNet developer.