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<title>Ipe Manual -- 9 Writing ipelets</title>
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<table width="100%" cellpadding=0 cellspacing=2><tr><td bgcolor="#99ccff"><a href="manual_31.html"><img border="0" alt="10 Troubleshooting the LaTeX-conversion" src="next.png"></a></td><td bgcolor="#99ccff"><a href="manual.html"><img border="0" alt="Top" src="up.png"></a></td><td bgcolor="#99ccff"><a href="manual_29.html"><img border="0" alt="8 Page views" src="previous.png"></a></td><td align="center" bgcolor="#99ccff" width="100%"><b>9 Writing ipelets</b></td></tr></table>
<h1>9 Writing ipelets</h1>
<p>An ipelet is a dynamically loaded library (DLL), that you place on
Ipe's ipelet search path. Ipe loads all DLLs it can find on that path
during start-up. The DLL has to be written in C++, and must export a
function <code>NewIpelet</code> that creates an object derived from the
class <code>Ipelet</code> (defined in <em>ipelet.h</em>). Here is minimal
ipelet implementation:
<pre>
#include "ipelet.h"
class MyIpelet : public Ipelet {
public:
virtual int IpelibVersion() const { return IPELIB_VERSION; }
virtual const char *Label() const { return "My label"; }
virtual void Run(IpePage *page, IpeletHelper *helper);
};
void MyIpelet::Run(int function, IpePage *page, IpeletHelper *helper)
{
// this is where you do all the work
}
IPELET_DECLARE Ipelet *NewIpelet()
{
return new MyIpelet;
}
</pre>
When the ipelet is executed, Ipe hands it a pointer to the current
page of the document. The ipelet can examine the selected objects,
and modify the page in any way it wishes. It can also request services
from the Ipe application through the <code>IpeHelper</code> object, for
instance to display a message in the status bar, to pop up message
boxes, to obtain input from the user, etc. Through the
<code>IpeHelper</code>, it is also possible to access the complete document
(for instance to write an ipelet that allows the user to reorganize
the pages of the document), or to access some Ipe settings.
<p>The Ipelib documentation in HTML-format is <a href="index.html">here</a>. You may want to have a look at
the standard ipelets. <em>Kgon</em>, for instance, is a minimal ipelet
that you can use as the basis for your own development.
<em>Goodies</em> is an example of an ipelet that contains more than one
function--it also needs to implement the member functions
<code>NumFunctions</code> and <code>SubLabel</code>. Note that it is possible for
ipelets to define keyboard shortcuts (the <em>Align</em> ipelet does
that, for instance), but in general it is not a good idea to do that
for ipelets you plan to make available for others.
<h4><a name="id1">Compiling ipelets on Windows</a></h4>
The ipelet must be compiled as a DLL and must be linked with the Ipe
library "libipe.lib". C++ mandates that it must be compiled with
the same compiler that was used to compile Ipe. If you use the binary
Ipe distribution for Windows, that means you have to use the free
Borland C++ compiler. (Its command-line version is available as a
download after registering on the <a href="http://www.borland.com">Borland
webpage</a>, the same compiler is also in Borland
C++ builder.) The Ipe Windows distribution contains the necessary
header files and the library to compile ipelets, as well as the source
of the "kgon" and "goodies" ipelets as examples. You can compile
the "kgon" example as follows:
<pre>
bcc32 -WD -tWR -DWIN32 -Iinclude kgon.cpp lib/libipe.lib
</pre>
Place the resulting <i>kgon.dll</i> in the <i>ipelets</i>
subdirectory, and restart Ipe.
<h4><a name="id2">Compiling ipelets on Unix</a></h4>
The ipelet must be compiled as a shared library and must be linked
with the Ipe library "libipe.so". C++ mandates that it must be
compiled with the same compiler that was used to compile Ipe. Have a
look at the ipelet sources in the Ipe source distribution, and their
project files for details on compiling them.
<hr />
<table width="100%" cellpadding=0 cellspacing=2><tr><td bgcolor="#99ccff"><a href="manual_31.html"><img border="0" alt="10 Troubleshooting the LaTeX-conversion" src="next.png"></a></td><td bgcolor="#99ccff"><a href="manual.html"><img border="0" alt="Top" src="up.png"></a></td><td bgcolor="#99ccff"><a href="manual_29.html"><img border="0" alt="8 Page views" src="previous.png"></a></td><td align="center" bgcolor="#99ccff" width="100%"><b>9 Writing ipelets</b></td></tr></table></body></html>
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