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90 lines
3.0 KiB
90 lines
3.0 KiB
Using Skia's PDF Backend
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========================
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Here is an example of using Skia's PDF backend (SkPDF) via the
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SkDocument and SkCanvas APIs.
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<!--?prettify lang=cc?-->
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#include "SkPDFDocument.h"
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void WritePDF(SkWStream* outputStream,
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const char* documentTitle,
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void (*writePage)(SkCanvas*, int page),
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int numberOfPages,
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SkSize pageSize) {
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SkPDF::Metadata metadata;
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metadata.fTitle = documentTitle;
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metadata.fCreator = "Example WritePDF() Function";
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SkTime::DateTime now;
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SkTime::GetDateTime(&now);
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metadata.fCreation = now;
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metadata.fModified = now;
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auto pdfDocument = SkPDF::MakeDocument(outputStream, metadata);
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assert(pdfDocument);
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for (int page = 0; page < numberOfPages; ++page) {
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SkCanvas* pageCanvas = pdfDocument->beginPage(pageSize.width(),
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pageSize.height());
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writePage(pageCanvas, page);
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pdfDocument->endPage();
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}
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pdfDocument->close();
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}
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* * *
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<span id="limits">SkPDF Limitations</span>
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------------------------------------------
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There are several corners of Skia's public API that SkPDF currently
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does not handle because either no known client uses the feature or
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there is no simple PDF-ish way to handle it.
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In this document:
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+ **drop** means to draw nothing.
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+ **ignore** means to draw without the effect
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+ **expand** means to implement something in a non-PDF-ish way.
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This may mean to rasterize vector graphics, to expand paths with
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path effects into many individual paths, or to convert text to
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paths.
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<style scoped><!--
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#pdftable {border-collapse:collapse;}
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#pdftable tr th, #pdftable tr td {border:#888888 2px solid;padding: 5px;}
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--></style>
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<table id="pdftable">
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<tr><th>Effect</th> <th>text</th> <th>images</th> <th>everything
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else</th></tr>
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<tr><th>SkMaskFilter</th> <td>drop</td> <td>ignore</td> <td>ignore</td></tr>
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<tr><th>SkPathEffect</th> <td>ignore</td> <td>n/a</td> <td>expand</td></tr>
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<tr><th>SkColorFilter</th> <td>ignore</td> <td>expand</td> <td>ignore</td></tr>
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<tr><th>SkImageFilter</th> <td>expand</td> <td>expand</td> <td>expand</td></tr>
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<tr><th>unsupported SkXferModes</th> <td>ignore</td> <td>ignore</td> <td>ignore</td></tr>
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<tr><th>non-gradient SkShader</th> <td>expand</td> <td>n/a</td> <td>expand</td></tr>
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</table>
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Notes:
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- *SkImageFilter*: When SkImageFilter is expanded, text-as-text is lost.
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- *SkXferMode*: The following transfer modes are not natively
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supported by PDF: DstOver, SrcIn, DstIn, SrcOut, DstOut, SrcATop,
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DstATop, and Modulate.
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Other limitations:
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- *drawText with VerticalText* — drop. No known clients seem to make use
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of the VerticalText flag.
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- *drawTextOnPath* — expand. (Text-as-text is lost.)
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- *drawVertices* — drop.
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- *drawPatch* — drop.
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* * *
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