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      1 Using Skia's PDF Backend
      2 ========================
      3 
      4 Here is an example of using Skia's PDF backend (SkPDF) via the
      5 SkDocument and SkCanvas APIs.
      6 
      7 <!--?prettify lang=cc?-->
      8 
      9     #include "SkPDFDocument.h"
     10 
     11     void WritePDF(SkWStream* outputStream,
     12                   const char* documentTitle,
     13                   void (*writePage)(SkCanvas*, int page),
     14                   int numberOfPages,
     15                   SkSize pageSize) {
     16         SkPDF::Metadata metadata;
     17         metadata.fTitle = documentTitle;
     18         metadata.fCreator = "Example WritePDF() Function";
     19         SkTime::DateTime now;
     20         SkTime::GetDateTime(&now);
     21         metadata.fCreation = now;
     22         metadata.fModified = now;
     23         auto pdfDocument = SkPDF::MakeDocument(outputStream, metadata);
     24         assert(pdfDocument);
     25 
     26         for (int page = 0; page < numberOfPages; ++page) {
     27             SkCanvas* pageCanvas = pdfDocument->beginPage(pageSize.width(),
     28                                                           pageSize.height());
     29             writePage(pageCanvas, page);
     30             pdfDocument->endPage();
     31         }
     32         pdfDocument->close();
     33     }
     34 
     35 * * *
     36 
     37 <span id="limits">SkPDF Limitations</span>
     38 ------------------------------------------
     39 
     40 There are several corners of Skia's public API that SkPDF currently
     41 does not handle because either no known client uses the feature or
     42 there is no simple PDF-ish way to handle it.
     43 
     44 In this document:
     45 
     46   + **drop** means to draw nothing.
     47 
     48   + **ignore** means to draw without the effect
     49 
     50   + **expand** means to implement something in a non-PDF-ish way.
     51     This may mean to rasterize vector graphics, to expand paths with
     52     path effects into many individual paths, or to convert text to
     53     paths.
     54 
     55 <style scoped><!--
     56 #pdftable {border-collapse:collapse;}
     57 #pdftable tr th, #pdftable tr td {border:#888888 2px solid;padding: 5px;}
     58 --></style>
     59 <table id="pdftable">
     60 <tr><th>Effect</th>                  <th>text</th>   <th>images</th> <th>everything
     61                                                                          else</th></tr>
     62 <tr><th>SkMaskFilter</th>            <td>drop</td>   <td>ignore</td> <td>ignore</td></tr>
     63 <tr><th>SkPathEffect</th>            <td>ignore</td> <td>n/a</td>    <td>expand</td></tr>
     64 <tr><th>SkColorFilter</th>           <td>ignore</td> <td>expand</td> <td>ignore</td></tr>
     65 <tr><th>SkImageFilter</th>           <td>expand</td> <td>expand</td> <td>expand</td></tr>
     66 <tr><th>unsupported SkXferModes</th> <td>ignore</td> <td>ignore</td> <td>ignore</td></tr>
     67 <tr><th>non-gradient SkShader</th>   <td>expand</td> <td>n/a</td>    <td>expand</td></tr>
     68 </table>
     69 
     70 Notes:
     71 
     72   - *SkImageFilter*: When SkImageFilter is expanded, text-as-text is lost.
     73 
     74   - *SkXferMode*: The following transfer modes are not natively
     75     supported by PDF: DstOver, SrcIn, DstIn, SrcOut, DstOut, SrcATop,
     76     DstATop, and Modulate.
     77 
     78 Other limitations:
     79 
     80   - *drawText with VerticalText*  drop. No known clients seem to make use
     81     of the VerticalText flag.
     82 
     83   - *drawTextOnPath*  expand. (Text-as-text is lost.)
     84 
     85   - *drawVertices*  drop.
     86 
     87   - *drawPatch*  drop.
     88 
     89 * * *
     90