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Using Skia's PDF Backend
========================
Here is an example of using Skia's PDF backend (SkPDF) via the
SkDocument and SkCanvas APIs.
<!--?prettify lang=cc?-->
#include "SkDocument.h"
void WritePDF(SkWStream* outputStream,
const char* documentTitle,
void (*writePage)(SkCanvas*, int page),
int numberOfPages,
SkSize pageSize) {
SkDocument::PDFMetadata metadata;
metadata.fTitle = documentTitle;
metadata.fCreator = "Example WritePDF() Function";
SkTime::DateTime now;
SkTime::GetDateTime(&now);
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);
for (int page = 0; page < numberOfPages; ++page) {
SkCanvas* pageCanvas =
pdfDocument->beginPage(pageSize.width(),
pageSize.height());
writePage(pageCanvas, page);
pdfDocument->endPage();
}
pdfDocument->close();
}
* * *
<span id="limits">SkPDF Limitations</span>
------------------------------------------
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.
<style scoped><!--
#pdftable {border-collapse:collapse;}
#pdftable tr th, #pdftable tr td {border:#888888 2px solid;padding: 5px;}
--></style>
<table id="pdftable">
<tr><th>Effect</th> <th>text</th> <th>images</th> <th>everything
else</th></tr>
<tr><th>SkMaskFilter</th> <td>drop</td> <td>ignore</td> <td>ignore</td></tr>
<tr><th>SkPathEffect</th> <td>ignore</td> <td>n/a</td> <td>expand</td></tr>
<tr><th>SkColorFilter</th> <td>ignore</td> <td>expand</td> <td>ignore</td></tr>
<tr><th>SkImageFilter</th> <td>expand</td> <td>expand</td> <td>expand</td></tr>
<tr><th>unsupported SkXferModes</th> <td>ignore</td> <td>ignore</td> <td>ignore</td></tr>
<tr><th>non-gradient SkShader</th> <td>expand</td> <td>n/a</td> <td>expand</td></tr>
</table>
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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