SVG paths in XSLT (was: Using W3C Regular Expressions)

[Robin Berjon <robin@knowscape.com>]

At 10:17 20/04/2001 +0100, Henry S. Thompson wrote:
>Robin Berjon <robin@knowscape.com> writes:
>> Size otoh is not really a good argument. Gz-compressed SVG is really small
>> (smaller than the other vector graphic formats that I've benchmarked it
>> against), and it wouldn't be much larger if paths used markup instead.
>> However, SVG paths wouldn't be much more humanly readable as markup than
>> they are as strings so that point is pretty moot in the context of SVG
>
>Disagree -- if they used markup I could use XSL(T) on them, which I
>would really like to do!

I was just addressing the points that had been listed, ie readability and
size. I wholeheartedly agree that being able to transform some path
vocabulary into SVG using XSLT is very interesting. As things stand now, I
don't think that it is impossible however.

Given the following vocabulary:

<path>
 <d>
   <moveto position='absolute' x='100' y='150' />
   <lineto position='relative' x='80' y='10' />
   <horizontal-lineto position='absolute' x='200' />
   <closepath />
 </d>
</path>

to be transformed into <path d='M 100 150 l 80 90 H 200 z' /> (if my SVG
isn't too rotten), the following XSLT seems to do the job (in Saxon):

<xsl:stylesheet xmlns:xsl='http://www.w3.org/1999/XSL/Transform' version='1.0'>

<xsl:output omit-xml-declaration='yes' />
<xsl:strip-space elements='*' />

<xsl:template match='path'>
 <xsl:element name='path'>
  <xsl:attribute name='d'>
   <xsl:apply-templates mode='in_path' />
  </xsl:attribute>
 </xsl:element>
</xsl:template>

<xsl:template match='moveto' mode='in_path'>
 <xsl:choose>
  <xsl:when test='@position="absolute"'><xsl:text>M </xsl:text></xsl:when>
  <xsl:otherwise><xsl:text>m </xsl:text></xsl:otherwise>
 </xsl:choose>

 <xsl:value-of select='@x' /><xsl:text> </xsl:text>
 <xsl:value-of select='@y' /><xsl:text> </xsl:text>
</xsl:template>

<xsl:template match='lineto' mode='in_path'>
 <xsl:choose>
  <xsl:when test='@position="absolute"'><xsl:text>L </xsl:text></xsl:when>
  <xsl:otherwise><xsl:text>l </xsl:text></xsl:otherwise>
 </xsl:choose>

 <xsl:value-of select='@x' /><xsl:text> </xsl:text>
 <xsl:value-of select='@y' /><xsl:text> </xsl:text>
</xsl:template>

<xsl:template match='horizontal-lineto' mode='in_path'>
 <xsl:choose>
  <xsl:when test='@position="absolute"'><xsl:text>H </xsl:text></xsl:when>
  <xsl:otherwise><xsl:text>h </xsl:text></xsl:otherwise>
 </xsl:choose>

 <xsl:value-of select='@x' /><xsl:text> </xsl:text>
</xsl:template>

<xsl:template match='closepath' mode='in_path'>
 <xsl:text>z</xsl:text>
</xsl:template>

</xsl:stylesheet>

So it is indeed possible. Another alternative would be to send the data
as-is within an SVG document and to put everything within the d element
(inclusive) inside a different namespace. You'd then simply
getElementsByTagNameNS your namespace and process their values using the
DOM to append to the path element's d attribute. I've used this technique
previously to extend SVG and it works marvels with Adobe's SVG viewer.

_______________________________________________________________________
Robin Berjon <robin@knowscape.com> -- CTO
k n o w s c a p e : // venture knowledge agency www.knowscape.com
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