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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.1//EN" "document-v11.dtd">
<document>
<header>
<title>SVG in FOP</title>
</header>
<body>
<section>
<title>Introduction</title>
<p>
FOP uses the SVG library from
<link href="http://xml.apache.org/batik/">Batik</link> to handle SVG.
This format can be handled as an <code>fo:instream-foreign-object</code>
or in a separate file referenced with <code>fo:external-graphic</code>.
Either way the SVG document will be read in and converted into a
DOM in Batik. This DOM will then be used by the renderer to
create the graphical image.
</p>
<p>
The AWT and Print renderers simply use batik to draw the SVG into a graphic.
</p>
<p>
In the case of the PDF renderer there is a PDFGraphics2D class that Batik uses
to render the image into. This class converts the drawing instructions into
PDF markup which is placed into the current PDF document.
</p>
</section>
<section>
<title>Converting SVG to a PDF Document</title>
<p>
It is possible to convert a standalone SVG document directly
into a simple page PDF document.
This is possible through the use of Batik's transcoder mechanism.<br/>
<code>java org.apache.batik.apps.rasterizer.Main -m application/pdf document.svg</code>
<br/>
This will output the svg document as "document.pdf" containing
a PDF rendering of the SVG file.
</p>
<p>
It is also possible to specify the width and/or height
of the PDF document on the command line with -w and -h or if
you are using the transcoder api you can use the transcoding hints.
</p>
<p>
Currently the SVG image is drawn at the SVG document size and
simply scaled in PDF to the new size. So the result may not be
the best possible. For example if you have any images or effects
it will draw them at the original resolution of the svg document.
When this is viewed in the pdf it will have an incorrect resolution
for the size of the pdf.
</p>
<p>
The size of the pdf file will also remain the same regardless of
what size the page is.
</p>
<p>
For more information see <link href="http://xml.apache.org/batik/">Batik</link>
for how transcoders work.
</p>
</section>
<!--
<section>
<title>Examples</title>
<p>
These examples illustrate a number of issues relating to conversion
to PDF:
<table>
<caption>SVG to PDF examples</caption>
<tr>
<th></th>
<th>svg file</th>
<th>png file</th>
<th>pdf result</th>
</tr>
<tr>
<td>images</td>
<td><link href="svg/images.svg">images.svg</link></td>
<td><link href="svg/images.png">images.png</link></td>
<td><link href="svg/images.pdf">images.pdf</link></td>
</tr>
<tr>
<td>svg linking</td>
<td><link href="svg/link.svg">link.svg</link></td>
<td><link href="svg/link.png">link.png</link></td>
<td><link href="svg/link.pdf">link.pdf</link></td>
</tr>
<tr>
<td>gradients and patterns</td>
<td><link href="svg/paints.svg">paints.svg</link></td>
<td><link href="svg/paints.png">paints.png</link></td>
<td><link href="svg/paints.pdf">paints.pdf</link></td>
</tr>
<tr>
<td>various text and effects on text</td>
<td><link href="svg/text.svg">text.svg</link></td>
<td><link href="svg/text.png">text.png</link></td>
<td><link href="svg/text.pdf">text.pdf</link></td>
</tr>
<tr>
<td>transparent objects</td>
<td><link href="svg/transparency.svg">transparency.svg</link></td>
<td><link href="svg/transparency.png">transparency.png</link></td>
<td><link href="svg/transparency.pdf">transparency.pdf</link></td>
</tr>
</table>
<p>
As can be seen most of the specific issues are handled.
</p>
<p>
<note>
You will need Acrobat 5.0 to see transparency.
</note>
</p>
<table>
<caption>XSL:FO to PDF examples</caption>
<tr>
<th></th>
<th>fo file</th>
<th>pdf result</th>
</tr>
<tr>
<td>embedding svg</td>
<td><link href="fo/embedding.fo">embedding.fo</link></td>
<td><link href="fo/embedding.fo.pdf">embedding.fo.pdf</link></td>
</tr>
</table>
</p>
</section>
-->
<section>
<title>Important Notes</title>
<p>
The svg is inserted into PDF by using PDF commands to draw and fill
lines and curves. This means that the graphical objects created with
this remain as vector graphics.
</p>
<p>
There are a number of SVG things that cannot be converted directly into
PDF. Parts of the graphic such as effects and images are inserted
into the PDF as a raster graphic. The resolution of this graphic may not
be ideal depending on the FOP dpi (72dpi) and the scaling for that graphic.
</p>
<p>
Another important note is that text may be converted and drawn as a
set of shapes by batik.
If possible it will use normal PDF text when inserting text. It does
this by checking if the text can be drawn normally and the font is
supported. This example svg <link href="svg/text.svg">text.svg</link> /
<link href="svg/text.pdf">text.pdf</link>
shows how various types and effects with text are handled.
</p>
<p>
If the text cannot be drawn normally then it uses shapes.
This means that a typical character will have about 10 curves
(each curve consists of at least 20 characters).
This can make the pdf files large and when the pdf is viewed the
viewer does not normally draw those fine curves very well (turning on
Smooth Line Art in the Acrobat preferences will fix this).
If the text is inserted into the PDF using the inbuilt text commands
for PDF it will use a single character.
</p>
</section>
<section>
<title>Known Problems</title>
<p>
<ul>
<li>
soft mask transparency is combined with white so that it looks better
on pdf 1.3 viewers but this causes the soft mask to be slightly lighter
or darker on pdf 1.4 viewers
</li>
<li>
there is some problem with a gradient inside a pattern causing a pdf
error when viewed in acrobat 5
</li>
<li>
text is not always handled correctly, it may select the wrong font
especially if characters have multiple fonts in the font list
</li>
<li>
more pdf text handling could be implemented
It could draw the string using the attributed character iterator
to handle tspans and other simple changes of text.
</li>
<li>
JPEG images are not inserted directly into the pdf document
This area has not been implemented yet since the appropriate
method in batik is static
</li>
<li>
Uniform transparency for images and other svg elements that are converted
into a raster graphic are not drawn properly in PDF. The image is opaque.
</li>
</ul>
</p>
</section>
<section>
<title>Developer Notes</title>
<p>
For most output formats in FOP the SVG is simply drawn into
an image with Batik.
For PDF there are a set of classes to handle drawing the
<link href="http://xml.apache.org/batik/architecture.html">GVT (Graphic Vector Toolkit)</link>
into PDF markup.
</p>
<section>
<title>Classes</title>
<p>
These are the relevant classes, found in the package org.apache.fop.svg :
</p>
<p>
<ul>
<li><em>PDFGraphics2D</em>
<br/>
used for drawing onto a Graphics2D into an existing pdf document, used
internally to draw the svg.
</li>
<li><em>PDFDocumentGraphics2D</em>
<br/>
used to create a pdf document and inherits from PDFGraphics2D to do the
rest of the drawing. Used by the transcoder to create a standalone pdf
document from an svg. Can be used independantly the same as any Graphics2D.
</li>
<li><em>PDFTranscoder</em>
<br/>
used by Batik to transcode an svg document into a standalone pdf, via
PDFDocumentGraphics2D.
</li>
</ul>
</p>
</section>
<section>
<title>Ideas</title>
<p>
Batik can convert ttf to svg font.
This svg font could be converted into a pdf stroked font
(type 3 font).
</p>
</section>
</section>
</body>
</document>
|
