Using Skia's PDF Backend

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

#include "SkPDFDocument.h"

void WritePDF(SkWStream* outputStream,
              const char* documentTitle,
              void (*writePage)(SkCanvas*, int page),
              int numberOfPages,
              SkSize pageSize) {
    SkPDF::Metadata metadata;
    metadata.fTitle = documentTitle;
    metadata.fCreator = "Example WritePDF() Function";
    SkTime::DateTime now;
    SkTime::GetDateTime(&now);
    metadata.fCreation = now;
    metadata.fModified = now;
    sk_sp<SkDocument> pdfDocument = SkPDF::MakeDocument(
            outputStream, SK_ScalarDefaultRasterDPI, metadata,
            nullptr, true);
    assert(pdfDocument);

    for (int page = 0; page < numberOfPages; ++page) {
        SkCanvas* pageCanvas =
                pdfDocument->beginPage(pageSize.width(),
                                       pageSize.height());
        writePage(pageCanvas, page);
        pdfDocument->endPage();
    }
    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 means 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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