skia2/site/user/sample/pdf.md

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, metadata);
    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.

Effect	text	images	everything else
SkMaskFilter	drop	ignore	ignore
SkPathEffect	ignore	n/a	expand
SkColorFilter	ignore	expand	ignore
SkImageFilter	expand	expand	expand
unsupported SkXferModes	ignore	ignore	ignore
non-gradient SkShader	expand	n/a	expand

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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