Using Skia's PDF Backend

Here is an example of using Skia's PDF backend (SkPDF) via the SkDocument and SkCanvas APIs.

#include "SkDocument.h"

bool WritePDF(SkWStream* outputStream) {
    SkDocument::PDFMetadata metadata;
    metadata.fCreator  = "creator....";
    metadata.fTitle    = "title...";
    metadata.fAuthor   = "author...";
    metadata.fSubject  = "subject...";
    metadata.fKeywords = "keywords...";
    metadata.fCreator  = "creator...";
    SkTime::DateTime now = get_current_date_and_time();
    metadata.fCreation.fEnabled = true;
    metadata.fCreation.fDateTime = now;
    metadata.fModified.fEnabled = true;
    metadata.fModified.fDateTime = now;
    sk_sp<SkDocument> pdfDocument(SkDocument::MakePDF(
            outputStream, SK_ScalarDefaultRasterDPI, metadata,
            nullptr, true);
    assert(pdfDocument);

    int numberOfPages = ....;
    for (int page = 0; page < numberOfPages; ++page) {
        SkScalar pageWidth = ....;
        SkScalar pageHeight = ....;
        SkCanvas* pageCanvas =
                pdfDocument->beginPage(pageWidth, pageHeight);

        // ....insert canvas draw commands here....

        pdfDocument->endPage();
    }
    return pdfDocument->close();
}

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SkPDF Limitations

There are several corners of Skia's public API that SkPDF currently does not handle because either no known client uses the feature or there is no simple PDF-ish way to handle it.

In this document:

• drop means to draw nothing.

• ignore mean to draw without the effect

• expand means to implement something in a non-PDF-ish way. This may mean to rasterize vector graphics, to expand paths with path effects into many individual paths, or to convert text to paths.

Notes:

• SkImageFilter: When SkImageFilter is expanded, text-as-text is lost.

• SkXferMode: The following transfer modes are not natively supported by PDF: DstOver, SrcIn, DstIn, SrcOut, DstOut, SrcATop, DstATop, and Modulate.

Other limitations:

• drawText with VerticalText — drop. No known clients seem to make use of the VerticalText flag.

• drawTextOnPath — expand. (Text-as-text is lost.)

• drawVertices — drop.

• drawPatch — drop.

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