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<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle">Minimal Module</span></h2>
<p>Minimal Module —
Dissection of a minimal <span class="application">Gwyddion</span> data
processing module
</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="id-1.3.3.3"></a><h2>Module Overview</h2>
<p>
In this section we will describe a minimal
<span class="application">Gwyddion</span> data-processing module.
It provides a function to invert values in a channel about zero.
The complete module code is:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
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53</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="preproc">#include</span><span class="normal"> </span><span class="string"><libgwyddion/gwymacros.h></span>
<span class="preproc">#include</span><span class="normal"> </span><span class="string"><libprocess/datafield.h></span>
<span class="preproc">#include</span><span class="normal"> </span><span class="string"><libgwymodule/gwymodule-process.h></span>
<span class="preproc">#include</span><span class="normal"> </span><span class="string"><libgwydgets/gwystock.h></span>
<span class="preproc">#include</span><span class="normal"> </span><span class="string"><app/gwyapp.h></span>
<span class="preproc">#define</span><span class="normal"> </span><span class="usertype">INVERT_VALUE_RUN_MODES</span><span class="normal"> <a href="libgwymodule-gwymoduleenums.html#GWY-RUN-IMMEDIATE:CAPS">GWY_RUN_IMMEDIATE</a></span>
<span class="keyword">static</span><span class="normal"> </span><span class="usertype">gboolean</span><span class="normal"> </span><span class="function">module_register</span><span class="symbol">(</span><span class="type">void</span><span class="symbol">);</span>
<span class="keyword">static</span><span class="normal"> </span><span class="type">void</span><span class="normal"> </span><span class="function">my_invert_value</span><span class="symbol">(</span><span class="usertype">GwyContainer</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">data</span><span class="symbol">,</span>
<span class="normal"> </span><span class="usertype">GwyRunType</span><span class="normal"> run</span><span class="symbol">);</span>
<span class="keyword">static</span><span class="normal"> </span><span class="usertype">GwyModuleInfo</span><span class="normal"> module_info </span><span class="symbol">=</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal"> <a href="libgwymodule-gwymoduleloader.html#GWY-MODULE-ABI-VERSION:CAPS">GWY_MODULE_ABI_VERSION</a></span><span class="symbol">,</span>
<span class="normal"> </span><span class="symbol">&</span><span class="normal">module_register</span><span class="symbol">,</span>
<span class="normal"> </span><span class="function"><a href="../libgwyddion/libgwyddion-gwymacros.html#N-:CAPS">N_</a></span><span class="symbol">(</span><span class="string">"Inverts data value."</span><span class="symbol">),</span>
<span class="normal"> </span><span class="string">"J. Random Hacker <hacker.jr@example.org>"</span><span class="symbol">,</span>
<span class="normal"> </span><span class="string">"1.0"</span><span class="symbol">,</span>
<span class="normal"> </span><span class="string">"Bit Rot Inc."</span><span class="symbol">,</span>
<span class="normal"> </span><span class="string">"2006"</span><span class="symbol">,</span>
<span class="cbracket">}</span><span class="symbol">;</span>
<span class="function"><a href="libgwymodule-gwymoduleloader.html#GWY-MODULE-QUERY:CAPS">GWY_MODULE_QUERY</a></span><span class="symbol">(</span><span class="normal">module_info</span><span class="symbol">)</span>
<span class="keyword">static</span><span class="normal"> <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gboolean">gboolean</a></span>
<span class="function">module_register</span><span class="symbol">(</span><span class="type">void</span><span class="symbol">)</span>
<span class="cbracket">{</span>
<span class="normal"> </span><span class="function"><a href="libgwymodule-gwymodule-process.html#gwy-process-func-register">gwy_process_func_register</a></span><span class="symbol">(</span><span class="string">"my_invert_value"</span><span class="symbol">,</span>
<span class="normal"> </span><span class="symbol">(</span><span class="normal"><a href="libgwymodule-gwymodule-process.html#GwyProcessFunc">GwyProcessFunc</a></span><span class="symbol">)&</span><span class="normal">my_invert_value</span><span class="symbol">,</span>
<span class="normal"> </span><span class="function"><a href="../libgwyddion/libgwyddion-gwymacros.html#N-:CAPS">N_</a></span><span class="symbol">(</span><span class="string">"/_Test/_Invert Value"</span><span class="symbol">),</span>
<span class="normal"> <a href="../libgwydgets/libgwydgets-gwystock.html#GWY-STOCK-VALUE-INVERT:CAPS">GWY_STOCK_VALUE_INVERT</a></span><span class="symbol">,</span>
<span class="normal"> INVERT_VALUE_RUN_MODES</span><span class="symbol">,</span>
<span class="normal"> <a href="../libgwyapp/libgwyapp-menu.html#GWY-MENU-FLAG-DATA:CAPS">GWY_MENU_FLAG_DATA</a></span><span class="symbol">,</span>
<span class="normal"> </span><span class="function"><a href="../libgwyddion/libgwyddion-gwymacros.html#N-:CAPS">N_</a></span><span class="symbol">(</span><span class="string">"Invert data value about origin"</span><span class="symbol">));</span>
<span class="normal"> </span><span class="keyword">return</span><span class="normal"> <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Standard-Macros.html#TRUE:CAPS">TRUE</a></span><span class="symbol">;</span>
<span class="cbracket">}</span>
<span class="keyword">static</span><span class="normal"> </span><span class="type">void</span>
<span class="function">my_invert_value</span><span class="symbol">(</span><span class="usertype">GwyContainer</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">data</span><span class="symbol">,</span>
<span class="normal"> </span><span class="usertype">GwyRunType</span><span class="normal"> run</span><span class="symbol">)</span>
<span class="cbracket">{</span>
<span class="normal"> </span><span class="usertype">GwyDataField</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">dfield</span><span class="symbol">;</span>
<span class="normal"> </span><span class="usertype">GQuark</span><span class="normal"> quark</span><span class="symbol">;</span>
<span class="normal"> </span><span class="function"><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="symbol">(</span><span class="normal">run </span><span class="symbol">&</span><span class="normal"> INVERT_VALUE_RUN_MODES</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-data-browser-get-current">gwy_app_data_browser_get_current</a></span><span class="symbol">(</span><span class="normal"><a href="../libgwyapp/libgwyapp-data-browser.html#GWY-APP-DATA-FIELD:CAPS">GWY_APP_DATA_FIELD</a></span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">dfield</span><span class="symbol">,</span>
<span class="normal"> <a href="../libgwyapp/libgwyapp-data-browser.html#GWY-APP-DATA-FIELD-KEY:CAPS">GWY_APP_DATA_FIELD_KEY</a></span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">quark</span><span class="symbol">,</span>
<span class="normal"> </span><span class="number">0</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="../libgwyapp/libgwyapp-undo.html#gwy-app-undo-qcheckpointv">gwy_app_undo_qcheckpointv</a></span><span class="symbol">(</span><span class="normal">data</span><span class="symbol">,</span><span class="normal"> </span><span class="number">1</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">quark</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="../libgwyprocess/GwyDataField.html#gwy-data-field-multiply">gwy_data_field_multiply</a></span><span class="symbol">(</span><span class="normal">dfield</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">-</span><span class="number">1.0</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="../libgwyprocess/GwyDataField.html#gwy-data-field-data-changed">gwy_data_field_data_changed</a></span><span class="symbol">(</span><span class="normal">dfield</span><span class="symbol">);</span>
<span class="cbracket">}</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
Though the above example is minimal it still constis of quite a bit of
code. We will analyse it piece-by-piece in the following paragraphs.
</p>
</div>
<div class="refsect1">
<a name="id-1.3.3.4"></a><h2>Boilerplate</h2>
<p>
First of all, of course, some header files.
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="preproc">#include</span><span class="normal"> </span><span class="string"><libgwyddion/gwymacros.h></span>
<span class="preproc">#include</span><span class="normal"> </span><span class="string"><libprocess/datafield.h></span>
<span class="preproc">#include</span><span class="normal"> </span><span class="string"><libgwymodule/gwymodule-process.h></span>
<span class="preproc">#include</span><span class="normal"> </span><span class="string"><libgwydgets/gwystock.h></span>
<span class="preproc">#include</span><span class="normal"> </span><span class="string"><app/gwyapp.h></span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
These four are essential, for a complex modules you may need additional
headers.
<code class="filename"><a href="../libgwyddion/libgwyddion-gwymacros.html">gwymacros.h</a></code>
contains some basic macros,
<code class="filename"><a href="../libgwyprocess/GwyDataField.html">datafield.h</a></code>
declares basic <a href="../libgwyprocess/GwyDataField.html"><span class="type">GwyDataField</span></a> methods,
<code class="filename"><a href="../libgwydgets/libgwydgets-gwystock.html">gwystock.h</a></code>
contains stock icon definitions,
<code class="filename">gwymodule-process.h</code>
declares functions essential for registering the module and its data processing functions,
and <code class="filename">gwyapp.h</code>
includes everything necessary for interfacing with the application.
</p>
</div>
<div class="refsect1">
<a name="id-1.3.3.5"></a><h2>Function Prototypes</h2>
<p>
Function prototypes of our functions.
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="keyword">static</span><span class="normal"> </span><span class="usertype">gboolean</span><span class="normal"> </span><span class="function">module_register</span><span class="symbol">(</span><span class="type">void</span><span class="symbol">);</span>
<span class="keyword">static</span><span class="normal"> </span><span class="type">void</span><span class="normal"> </span><span class="function">my_invert_value</span><span class="symbol">(</span><span class="usertype">GwyContainer</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">data</span><span class="symbol">,</span>
<span class="normal"> </span><span class="usertype">GwyRunType</span><span class="normal"> run</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
Note <span class="emphasis"><em>all</em></span> functions and global variables should be
declared <code class="literal">static</code>, the module should export no symbol
except <a class="link" href="libgwymodule-gwymoduleloader.html#GWY-MODULE-QUERY:CAPS" title="GWY_MODULE_QUERY()"><code class="literal">GWY_MODULE_QUERY</code></a> described below.
</p>
<p>
An attentive reader has probably noticed we omitted the line
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="preproc">#define</span><span class="normal"> </span><span class="usertype">INVERT_VALUE_RUN_MODES</span><span class="normal"> <a href="libgwymodule-gwymoduleenums.html#GWY-RUN-IMMEDIATE:CAPS">GWY_RUN_IMMEDIATE</a></span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
where so-called run mode is defined. We will describe run modes in
detail in the <a class="link" href="gwymodule-tutorial-process.html" title="Data Processing Modules">section about
data processing modules</a>. At this point it suffices to say
<a class="link" href="libgwymodule-gwymoduleenums.html#GWY-RUN-IMMEDIATE:CAPS"><code class="literal">GWY_RUN_IMMEDIATE</code></a> means the function is non-interactive, executed
immediately.
</p>
</div>
<div class="refsect1">
<a name="id-1.3.3.6"></a><h2>The Module Info Structure</h2>
<p>
Here the interesting part starts. The <a class="link" href="libgwymodule-gwymoduleloader.html#GwyModuleInfo" title="struct GwyModuleInfo"><span class="type">GwyModuleInfo</span></a> structure contains
overall information about the module, most of it is presented in
a more-or-less human-readable form in <span class="application">Gwyddion</span>
in the module browser.
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
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5
6
7
8
9</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="keyword">static</span><span class="normal"> </span><span class="usertype">GwyModuleInfo</span><span class="normal"> module_info </span><span class="symbol">=</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal"> <a href="libgwymodule-gwymoduleloader.html#GWY-MODULE-ABI-VERSION:CAPS">GWY_MODULE_ABI_VERSION</a></span><span class="symbol">,</span>
<span class="normal"> </span><span class="symbol">&</span><span class="normal">module_register</span><span class="symbol">,</span>
<span class="normal"> </span><span class="function"><a href="../libgwyddion/libgwyddion-gwymacros.html#N-:CAPS">N_</a></span><span class="symbol">(</span><span class="string">"Inverts data value."</span><span class="symbol">),</span>
<span class="normal"> </span><span class="string">"J. Random Hacker <hacker.jr@example.org>"</span><span class="symbol">,</span>
<span class="normal"> </span><span class="string">"1.0"</span><span class="symbol">,</span>
<span class="normal"> </span><span class="string">"Bit Rot Inc."</span><span class="symbol">,</span>
<span class="normal"> </span><span class="string">"2006"</span><span class="symbol">,</span>
<span class="cbracket">}</span><span class="symbol">;</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
The first item is always <a class="link" href="libgwymodule-gwymoduleloader.html#GWY-MODULE-ABI-VERSION:CAPS" title="GWY_MODULE_ABI_VERSION"><code class="literal">GWY_MODULE_ABI_VERSION</code></a>. The ABI version
compiled to the module is checked by the loader on load-time and
modules with wrong ABI version are rejected.
</p>
<p>
The second item is a pointer to module registration function, by
convention called <code class="function">module_register</code>. It is described
in details below.
</p>
<p>
The fourth item is module description. It will appear as Description
in the module browser. This is a short text (up to a paragraph or two)
informing curious humans what the module contains and/or does.
</p>
<p>
The next item is the module author(s). Under normal circumstances this
should be a name of a person (or more people). Including a contact
e-mail address here it's a good idea because it will appear in the
browser as Authors, so people don't need to look to the module sources
to find out how to contact you.
</p>
<p>
The next item is the module version, a free-form string that will
appear as Version in the browser. Though it is free-form, using a
versioning scheme with alorithmically comparable versions is
preferable.
</p>
<p>
The last but one and last items are the module copyright and date.
The copyright field may be the same as authors field (except without
the e-mail address), it may be an organization, or whoever owns the
copyright.
</p>
</div>
<div class="refsect1">
<a name="id-1.3.3.7"></a><h2>The Module Query Function</h2>
<p>
A <span class="application">Gwyddion</span> module is loaded in two stages.
First, it is queried, the module responds with its module info,
<span class="application">Gwyddion</span> then performs some basic sanity
checks (e.g., whether module ABI version matches). If it looks all
right, <span class="application">Gwyddion</span> continues with the
registration of particular module features.
</p>
<p>
The query function should be always constructed using the
<a class="link" href="libgwymodule-gwymoduleloader.html#GWY-MODULE-QUERY:CAPS" title="GWY_MODULE_QUERY()"><code class="literal">GWY_MODULE_QUERY</code></a> macro as follows (note there is <span class="emphasis"><em>no</em></span>
semicolon after the right parenthesis):
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="function"><a href="libgwymodule-gwymoduleloader.html#GWY-MODULE-QUERY:CAPS">GWY_MODULE_QUERY</a></span><span class="symbol">(</span><span class="normal">module_info</span><span class="symbol">)</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
The <em class="parameter"><code>module_info</code></em> parameter is the module info
described above. If you change its name for any reason, change it here
too.
</p>
</div>
<div class="refsect1">
<a name="id-1.3.3.8"></a><h2>Module Feature Registration</h2>
<p>
The module registration function is called in the second registration
stage and is responsible for registering particular module functions,
each in one turn. Our sample module registeres only a one function,
<code class="function">my_invert_value</code>.
</p>
<p>
Each function type has its own registration function, our function
is a data processing one, so it's registered with
<a class="link" href="libgwymodule-gwymodule-process.html#gwy-process-func-register" title="gwy_process_func_register ()"><code class="function">gwy_process_func_register()</code></a>.
File loading and/or saving functions are registered with
<a class="link" href="libgwymodule-gwymodule-file.html#gwy-file-func-register" title="gwy_file_func_register ()"><code class="function">gwy_file_func_register()</code></a>, etc.
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5
6
7
8
9
10
11
12
13</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="keyword">static</span><span class="normal"> <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gboolean">gboolean</a></span>
<span class="function">module_register</span><span class="symbol">(</span><span class="type">void</span><span class="symbol">)</span>
<span class="cbracket">{</span>
<span class="normal"> </span><span class="function"><a href="libgwymodule-gwymodule-process.html#gwy-process-func-register">gwy_process_func_register</a></span><span class="symbol">(</span><span class="string">"my_invert_value"</span><span class="symbol">,</span>
<span class="normal"> </span><span class="symbol">(</span><span class="normal"><a href="libgwymodule-gwymodule-process.html#GwyProcessFunc">GwyProcessFunc</a></span><span class="symbol">)&</span><span class="normal">my_invert_value</span><span class="symbol">,</span>
<span class="normal"> </span><span class="function"><a href="../libgwyddion/libgwyddion-gwymacros.html#N-:CAPS">N_</a></span><span class="symbol">(</span><span class="string">"/_Test/_Invert Value"</span><span class="symbol">),</span>
<span class="normal"> <a href="../libgwydgets/libgwydgets-gwystock.html#GWY-STOCK-VALUE-INVERT:CAPS">GWY_STOCK_VALUE_INVERT</a></span><span class="symbol">,</span>
<span class="normal"> INVERT_VALUE_RUN_MODES</span><span class="symbol">,</span>
<span class="normal"> <a href="../libgwyapp/libgwyapp-menu.html#GWY-MENU-FLAG-DATA:CAPS">GWY_MENU_FLAG_DATA</a></span><span class="symbol">,</span>
<span class="normal"> </span><span class="function"><a href="../libgwyddion/libgwyddion-gwymacros.html#N-:CAPS">N_</a></span><span class="symbol">(</span><span class="string">"Invert data value about origin"</span><span class="symbol">));</span>
<span class="normal"> </span><span class="keyword">return</span><span class="normal"> <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Standard-Macros.html#TRUE:CAPS">TRUE</a></span><span class="symbol">;</span>
<span class="cbracket">}</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
The registration function normally returns <code class="literal">TRUE</code>.
Returning <code class="literal">FALSE</code> means the registration failed, and
<span class="application">Gwyddion</span> then attempts to unregister all its
already registered functions, unload the module and proceed as if it
didn't exist.
</p>
</div>
<div class="refsect1">
<a name="id-1.3.3.9"></a><h2>Executive</h2>
<p>
Now let's do some actuall data processing:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5
6
7
8
9
10
11
12
13
14
15</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="keyword">static</span><span class="normal"> </span><span class="type">void</span>
<span class="function">my_invert_value</span><span class="symbol">(</span><span class="usertype">GwyContainer</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">data</span><span class="symbol">,</span>
<span class="normal"> </span><span class="usertype">GwyRunType</span><span class="normal"> run</span><span class="symbol">)</span>
<span class="cbracket">{</span>
<span class="normal"> </span><span class="usertype">GwyDataField</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">dfield</span><span class="symbol">;</span>
<span class="normal"> </span><span class="usertype">GQuark</span><span class="normal"> quark</span><span class="symbol">;</span>
<span class="normal"> </span><span class="function"><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a></span><span class="symbol">(</span><span class="normal">run </span><span class="symbol">&</span><span class="normal"> INVERT_VALUE_RUN_MODES</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-data-browser-get-current">gwy_app_data_browser_get_current</a></span><span class="symbol">(</span><span class="normal"><a href="../libgwyapp/libgwyapp-data-browser.html#GWY-APP-DATA-FIELD:CAPS">GWY_APP_DATA_FIELD</a></span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">dfield</span><span class="symbol">,</span>
<span class="normal"> <a href="../libgwyapp/libgwyapp-data-browser.html#GWY-APP-DATA-FIELD-KEY:CAPS">GWY_APP_DATA_FIELD_KEY</a></span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">quark</span><span class="symbol">,</span>
<span class="normal"> </span><span class="number">0</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="../libgwyapp/libgwyapp-undo.html#gwy-app-undo-qcheckpointv">gwy_app_undo_qcheckpointv</a></span><span class="symbol">(</span><span class="normal">data</span><span class="symbol">,</span><span class="normal"> </span><span class="number">1</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">quark</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="../libgwyprocess/GwyDataField.html#gwy-data-field-multiply">gwy_data_field_multiply</a></span><span class="symbol">(</span><span class="normal">dfield</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">-</span><span class="number">1.0</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="../libgwyprocess/GwyDataField.html#gwy-data-field-data-changed">gwy_data_field_data_changed</a></span><span class="symbol">(</span><span class="normal">dfield</span><span class="symbol">);</span>
<span class="cbracket">}</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
A few things can be seen here. First, we check the run mode we were
executed in. More sofisticated modules can in principle do different
things based on the run mode, but we just check whether it looks sane.
</p>
<p>
Next, we get the data field to operate on. The notion of current object
is maintained by the application
<a href="../libgwyapp/libgwyapp-data-browser.html">data browser</a> therefore we us
a data browser method (beside the current data field, we also ask for its
key that will be useful for undo later).
</p>
<p>
<a href="../libgwyprocess/GwyDataField.html"><span class="type">GwyDataField</span></a> is the basic data object representing a two-dimensional
array of values (typically a height field). Quite a few datafield
manipulating functions already exist in libprocess, we will use one of them
to perform the value inversion.
</p>
<p>
Function <a href="../libgwyapp/libgwyapp-undo.html#gwy-app-undo-qcheckpointv"><code class="function">gwy_app_undo_qcheckpointv()</code></a> creates a point in the undo history
we can return to later. It is necessary to call it before we start
modifying the data. Its first argument is the
<a href="../libgwyddion/GwyContainer.html">data container</a> the objects we will
change reside in. Then we pass the number of changed items (1) and
an array of their indentifiers in the data container.
</p>
<p>
Then we finally invert the value with <a href="../libgwyprocess/GwyDataField.html#gwy-data-field-multiply"><code class="function">gwy_data_field_multiply()</code></a> and we are
done – almost. To notify views displaying our data field that its data
has changed we call <a href="../libgwyprocess/GwyDataField.html#gwy-data-field-data-changed"><code class="function">gwy_data_field_data_changed()</code></a>. This function should
be called once on each changed data field after all processing is done.
</p>
</div>
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