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<H2><A NAME="6_3">6.3 Using the cache with Client Side Image Maps</A></H2>
<P> You can also use the cache system for CSIM as well. The cache system
 interface is slightly different in this case since the cache needs to
 store<STRONG> both</STRONG> the cached image and the cached image-map.
 It also needs to change due to the way CSIM HTML paradigm work. The two
 major differences from the &quot;standard&quot; cache is</P>
<OL>
<LI> The cached version will<STRONG> not</STRONG> be stored in the
 previous defined cache directory. See more below.</LI>
<LI> You must call an extra method, CheckCSIMCache(), to check the
 cache, see more below.</LI>
</OL>
<P></P>
<P> The performance benefits even for simple CSIM images is around 50%
 if the cache can be used and can of course be several 1000% if
 construction of the image requires DB calls and other complex
 operations which can be avoided.</P>
<P> Before reading further you should have an understanding on how the
 CSIM works by reading the section &quot;sing Client side image maps&quot;.</P>
<P> Please remember that when using CSIM you must end your script with a
 call to <A href="">Graph::StrokeCSIM()</A> method instead of the <A href="">
Graph::Stroke()</A> used for non-csim.</P>
<P> To use the cache with CSIM you have to call the <A href="">
Graph::CheckCSIMCache()</A>. As with the caching for non-CSIM you have
 to supply a name to be used for the cached version as well as an
 optional timeout value. The default timeout value if nothing else is
 specified is 60 minutes.</P>
<P> The name argument requires some more explanations. You must specify
 a relative name here. For example &quot;myimage&quot; or perhaps
 &quot;firstpage/image3&quot;. Depending on your installation of JpGraph this will
 now end up in the directory specified in the CSIMCACHE_DIR define. This
 must also be a directory accessible by the normal web server. By
 default a directory called &quot;csimcache&quot; will be created in the same
 directory as the image script itself.</P>
<P> This has the drawback that the directory from where the script is
 executed must be writable by the process running PHP. Best practice for
 this is to keep the number of writable directory for PHP down to a
 minimum and re-use the same directory as is used for the standard
 cache. This however, require that your system administrator setup that
 cache directory so that it also accessible by the HTTP server from the
 htdocs root.</P>
<P> The CheckCSIMCache() method checks the cache for an existing cached
 version and if found it returns it and halts execution of the script.
 So, this call should be the first call after the creation of the
 Graph() and before any heavy work is done to create the image so that
 you can minimize the execution of the script in the case a match is
 found.</P>
<P> So, the general structure of a script that uses CSIM and the cache
 is<DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
&nbsp;$graph&nbsp;</FONT><FONT color="#007700">=&nbsp;new&nbsp;</FONT><FONT color="#0000BB">
Graph</FONT><FONT color="#007700">(</FONT><FONT color="#0000BB">400</FONT><FONT
color="#007700">,</FONT><FONT color="#0000BB">300</FONT><FONT color="#007700">
);
<BR>
<BR></FONT><FONT color="#FF8000">//&nbsp;Check&nbsp;cache,&nbsp;10&nbsp;min&nbsp;timeout
<BR></FONT><FONT color="#0000BB">$graph</FONT><FONT color="#007700">-&gt;</FONT><FONT
color="#0000BB">CheckCSIMCache</FONT><FONT color="#007700">(</FONT><FONT color="#DD0000">
&quot;image1&quot;</FONT><FONT color="#007700">,</FONT><FONT color="#0000BB">10</FONT><FONT
color="#007700">);
<BR>
<BR></FONT><FONT color="#FF8000">
//&nbsp;!!&nbsp;If&nbsp;cached&nbsp;version&nbsp;exists,&nbsp;execution&nbsp;halts&nbsp;here&nbsp;!!
<BR>
<BR>//
<BR>//&nbsp;...&nbsp;Construct&nbsp;the&nbsp;image&nbsp;with&nbsp;heavy&nbsp;DB&nbsp;calls&nbsp;etc,&nbsp;etc
<BR>//
<BR>
<BR></FONT><FONT color="#0000BB">$graph</FONT><FONT color="#007700">-&gt;</FONT><FONT
color="#0000BB">StrokeCSIM</FONT><FONT color="#007700">();</FONT><FONT color="#0000BB">
</FONT></FONT></CODE></DIV></P>
<P> Please note that you<STRONG> do not</STRONG> need to pass any
 argument to the final call to StrokeCSIM() as you do when not using the
 cache.<DIV class="note"><B>Note:</B> The CSIM caching works by storing
 two files in the cache directory. One file being the image and the
 other file being the corresponding image map as a pure HTML file.</DIV></P>
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