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<div class="refentry">
<a name="gwymodule-tutorial-process"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle">Data Processing Modules</span></h2>
<p>Data Processing Modules —
More about data processing modules
</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="id-1.3.5.3"></a><h2>Run Modes</h2>
<p>
<a class="link" href="libgwymodule-gwymoduleenums.html#GwyRunType" title="enum GwyRunType">Run modes</a> specify how a module function
can be run. Data processing functions have two possible run modes.
</p>
<p>
If the function presents a (modal) dialog in which the user can for
instance adjust parameter values or make selections, include
<a class="link" href="libgwymodule-gwymoduleenums.html#GWY-RUN-INTERACTIVE:CAPS"><code class="literal">GWY_RUN_INTERACTIVE</code></a> flag in its run modes.
If it makes sense to be run without asking, include <a class="link" href="libgwymodule-gwymoduleenums.html#GWY-RUN-IMMEDIATE:CAPS"><code class="literal">GWY_RUN_IMMEDIATE</code></a>
flag in its run modes. When a function is run in immediate mode, it
should fetch the last used parameter values from settings as if it is
run interactively.
</p>
<p>
Many functions allow both modes and behave according to the mode
they were called in. The logic typically looks as follows:
</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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30</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">function</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">FunctionArgs</span><span class="normal"> args</span><span class="symbol">;</span>
<span class="normal"> </span><span class="usertype">GwyDataField</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">data_field</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="usertype">gboolean</span><span class="normal"> ok</span><span class="symbol">;</span>
<span class="normal"> </span><span class="comment">/* Check run mode */</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"> FUNCTION_RUN_MODES</span><span class="symbol">);</span>
<span class="normal"> </span><span class="comment">/* Get data field to operate on */</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-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"> <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">data_field</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="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">data_field </span><span class="symbol">&&</span><span class="normal"> quark</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function">load_args</span><span class="symbol">(</span><span class="function"><a href="../libgwyapp/libgwyapp-settings.html#gwy-app-settings-get">gwy_app_settings_get</a></span><span class="symbol">(),</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">args</span><span class="symbol">);</span>
<span class="normal"> </span><span class="comment">/* Present a GUI in interactive mode, quit if cancelled */</span>
<span class="normal"> </span><span class="keyword">if</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">run </span><span class="symbol">==</span><span class="normal"> <a href="libgwymodule-gwymoduleenums.html#GWY-RUN-INTERACTIVE:CAPS">GWY_RUN_INTERACTIVE</a></span><span class="symbol">)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal"> ok </span><span class="symbol">=</span><span class="normal"> </span><span class="function">function_dialog</span><span class="symbol">(&</span><span class="normal">args</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function">save_args</span><span class="symbol">(</span><span class="function"><a href="../libgwyapp/libgwyapp-settings.html#gwy-app-settings-get">gwy_app_settings_get</a></span><span class="symbol">(),</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">args</span><span class="symbol">);</span>
<span class="normal"> </span><span class="keyword">if</span><span class="normal"> </span><span class="symbol">(!</span><span class="normal">ok</span><span class="symbol">)</span>
<span class="normal"> </span><span class="keyword">return</span><span class="symbol">;</span>
<span class="normal"> </span><span class="cbracket">}</span>
<span class="normal"> </span><span class="comment">/* Perform the processing in immediate mode, or after user confirmation */</span>
<span class="normal"> </span><span class="function">function_do</span><span class="symbol">(</span><span class="normal">data</span><span class="symbol">,</span><span class="normal"> data_field</span><span class="symbol">,</span><span class="normal"> quark</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">args</span><span class="symbol">);</span>
<span class="cbracket">}</span></pre></td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="refsect1">
<a name="id-1.3.5.4"></a><h2>Masks</h2>
<p>
To highlight some areas in the data (like the grain modules do) you may
want to use a mask. Masks are data fields too, differing only by a few
things from the ordinary ones. Standalone masks do not exist in the
container, they are always associated with some channel data. Mask data
field units are irrelevant – the value range is always from 0 to 1;
0 being fully transparent and 1 the mask color set by user (may not be
fully opaque). It should be noted that values different from 0 and 1 at
present do not have a well-defined meaning and current modules generally
produce and handle only values 0 and 1.
</p>
<p>
To attach a mask to a data field with id <span class="symbol">id</span>, just create
a new data field and put it to the container at the appropriate key which
can be obtained with <a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-get-mask-key-for-id"><code class="function">gwy_app_get_mask_key_for_id()</code></a>.
</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
10</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="usertype">GwyDataField</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">mask_field</span><span class="symbol">;</span>
<span class="usertype">GQuark</span><span class="normal"> quark</span><span class="symbol">;</span>
<span class="normal">mask_field </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="../libgwyprocess/GwyDataField.html#gwy-data-field-new-alike">gwy_data_field_new_alike</a></span><span class="symbol">(</span><span class="normal">data_field</span><span class="symbol">,</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="comment">/* Fill mask_field with the mask */</span>
<span class="symbol">...</span>
<span class="normal">quark </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-get-mask-key-for-id">gwy_app_get_mask_key_for_id</a></span><span class="symbol">(</span><span class="normal">id</span><span class="symbol">);</span>
<span class="function"><a href="../libgwyddion/GwyContainer.html#gwy-container-set-object">gwy_container_set_object</a></span><span class="symbol">(</span><span class="normal">container</span><span class="symbol">,</span><span class="normal"> quark</span><span class="symbol">,</span><span class="normal"> mask_field</span><span class="symbol">);</span>
<span class="function"><a href="http://developer.gnome.org/doc/API/2.0/gobject/gobject-The-Base-Object-Type.html#g-object-unref">g_object_unref</a></span><span class="symbol">(</span><span class="normal">mask_field</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
If you functions takes a mask as an input (e.g., as Grain Statistics
does), it should add <a href="../libgwyapp/libgwyapp-menu.html#GWY-MENU-FLAG-DATA-MASK:CAPS"><code class="literal">GWY_MENU_FLAG_DATA_MASK</code></a> to its sensitivity flags.
The application will then make its menu item and/or toolbox button
insensitive when no mask is available.
</p>
<p>
The mask of current channel and its key can be obtained with
<a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-data-browser-get-current"><code class="function">gwy_app_data_browser_get_current()</code></a> as usual.
</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="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-MASK-FIELD:CAPS">GWY_APP_MASK_FIELD</a></span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">mask_field</span><span class="symbol">,</span>
<span class="normal"> <a href="../libgwyapp/libgwyapp-data-browser.html#GWY-APP-MASK-FIELD-KEY:CAPS">GWY_APP_MASK_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></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
The function will set <span class="symbol">mask_field</span> to <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> and
<span class="symbol">quark</span> to 0 if the mask does not exist.
</p>
</div>
<div class="refsect1">
<a name="id-1.3.5.5"></a><h2>Presentations</h2>
<p>
Presentations are means to display some data derived from channel data
(or even completely unrelated data) to the user instead of the actual
data, while all other processing methods and tools still can see and work
on the real data. An example is Shader module.
</p>
<p>
Working with presentations is similar to masks. One only uses
<a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-get-show-key-for-id"><code class="function">gwy_app_get_show_key_for_id()</code></a> instead of <a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-get-mask-key-for-id"><code class="function">gwy_app_get_mask_key_for_id()</code></a>
(most functions working with presentations have <code class="literal">show</code>
in their name for <code class="literal">presentation</code> is just too long) to
obtain the presentation key, and uses <a href="../libgwyapp/libgwyapp-data-browser.html#GWY-APP-SHOW-FIELD:CAPS"><code class="literal">GWY_APP_SHOW_FIELD</code></a> and
<a href="../libgwyapp/libgwyapp-data-browser.html#GWY-APP-SHOW-FIELD-KEY:CAPS"><code class="literal">GWY_APP_SHOW_FIELD_KEY</code></a> when requesting the current presentation and its
key. Likewise one should add <a href="../libgwyapp/libgwyapp-menu.html#GWY-MENU-FLAG-DATA-SHOW:CAPS"><code class="literal">GWY_MENU_FLAG_DATA_SHOW</code></a> to menu
sensitivity flags of a function which processes presentations (this is
seldom needed as most functions only create presentations).
</p>
</div>
<div class="refsect1">
<a name="id-1.3.5.6"></a><h2>Data Previews</h2>
<p>
Data previews in module dialogs are best realized with <a href="../libgwydgets/GwyDataView.html"><span class="type">GwyDataView</span></a>
widget which is used for two-dimensional data displays everywhere else
in <span class="application">Gwyddion</span>. This widget is a bit complex,
but we can often simplify things a lot in a module dialog. The basic
scheme is following:
</p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
Create a local <a href="../libgwyddion/GwyContainer.html"><span class="type">GwyContainer</span></a> that will hold the objects to display.
On rare occasions we can directly display data from the application's
data container, but normally we are going to modify the data and
therefore a local object is needed.
</li>
<li class="listitem">
Fill it with objects. If our function does not change a data field
it is easier and more efficient to just put it to the private container
too, modifiable objects have to be duplicated. Since the container is
private, we are free to put anything anywhere, but to take advantage
of convenience data browser functions, we rather keep the application's
naming scheme and make the data field the 0th channel.
</li>
<li class="listitem">
Construct the <a href="../libgwydgets/GwyDataView.html"><span class="type">GwyDataView</span></a>. We have to put at least one layer there,
namely <a href="../libgwydgets/GwyLayerBasic.html"><span class="type">GwyLayerBasic</span></a> and set it up to display our data field.
To display mask we must add <a href="../libgwydgets/GwyLayerMask.html"><span class="type">GwyLayerMask</span></a> too, and for interactive
selections a <a href="../libgwydgets/standard-vector-layers.html">vector layer</a>
must be added.
</li>
<li class="listitem">
When the data of a displayed data field changes, we call
<a href="../libgwyprocess/GwyDataField.html#gwy-data-field-data-changed"><code class="function">gwy_data_field_data_changed()</code></a> to notify its users.
</li>
</ol></div>
<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
16
17
18
19
20
21
22
23
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25
26
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28
29
30</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="usertype">GtkWidget</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">data_view</span><span class="symbol">;</span>
<span class="usertype">GwyPixmapLayer</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">layer</span><span class="symbol">;</span>
<span class="usertype">GwyContainer</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">mydata</span><span class="symbol">;</span>
<span class="usertype">gdouble</span><span class="normal"> zoomval</span><span class="symbol">;</span>
<span class="comment">/* Create new container */</span>
<span class="normal">mydata </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="../libgwyddion/GwyContainer.html#gwy-container-new">gwy_container_new</a></span><span class="symbol">();</span>
<span class="comment">/* Fill it with objects and auxiliary data, dfield and id were obtained</span>
<span class="comment"> * before. */</span>
<span class="function"><a href="../libgwyddion/GwyContainer.html#gwy-container-set-object-by-name">gwy_container_set_object_by_name</a></span><span class="symbol">(</span><span class="normal">mydata</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"/0/data"</span><span class="symbol">,</span><span class="normal"> dfield</span><span class="symbol">);</span>
<span class="function"><a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-sync-data-items">gwy_app_sync_data_items</a></span><span class="symbol">(</span><span class="normal">data</span><span class="symbol">,</span><span class="normal"> mydata</span><span class="symbol">,</span><span class="normal"> id</span><span class="symbol">,</span><span class="normal"> </span><span class="number">0</span><span class="symbol">,</span><span class="normal"> <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Standard-Macros.html#FALSE:CAPS">FALSE</a></span><span class="symbol">,</span>
<span class="normal"> <a href="../libgwyapp/libgwyapp-data-browser.html#GWY-DATA-ITEM-PALETTE:CAPS">GWY_DATA_ITEM_PALETTE</a></span><span class="symbol">,</span>
<span class="normal"> <a href="../libgwyapp/libgwyapp-data-browser.html#GWY-DATA-ITEM-MASK-COLOR:CAPS">GWY_DATA_ITEM_MASK_COLOR</a></span><span class="symbol">,</span>
<span class="normal"> <a href="../libgwyapp/libgwyapp-data-browser.html#GWY-DATA-ITEM-RANGE:CAPS">GWY_DATA_ITEM_RANGE</a></span><span class="symbol">,</span>
<span class="normal"> </span><span class="number">0</span><span class="symbol">);</span>
<span class="comment">/* Create the data view and its layers */</span>
<span class="normal">data_view </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="../libgwydgets/GwyDataView.html#gwy-data-view-new">gwy_data_view_new</a></span><span class="symbol">(</span><span class="normal">mydata</span><span class="symbol">);</span>
<span class="normal">layer </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="../libgwydgets/GwyLayerBasic.html#gwy-layer-basic-new">gwy_layer_basic_new</a></span><span class="symbol">();</span>
<span class="function"><a href="../libgwydgets/GwyPixmapLayer.html#gwy-pixmap-layer-set-data-key">gwy_pixmap_layer_set_data_key</a></span><span class="symbol">(</span><span class="normal">layer</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"/0/data"</span><span class="symbol">);</span>
<span class="function"><a href="../libgwydgets/GwyLayerBasic.html#gwy-layer-basic-set-gradient-key">gwy_layer_basic_set_gradient_key</a></span><span class="symbol">(</span><span class="function">GWY_LAYER_BASIC</span><span class="symbol">(</span><span class="normal">layer</span><span class="symbol">),</span><span class="normal"> </span><span class="string">"/0/base/palette"</span><span class="symbol">);</span>
<span class="function"><a href="../libgwydgets/GwyDataView.html#gwy-data-view-set-base-layer">gwy_data_view_set_base_layer</a></span><span class="symbol">(</span><span class="function">GWY_DATA_VIEW</span><span class="symbol">(</span><span class="normal">data_view</span><span class="symbol">),</span><span class="normal"> layer</span><span class="symbol">);</span>
<span class="comment">/* Calculate preview size */</span>
<span class="normal">zoomval </span><span class="symbol">=</span><span class="normal"> PREVIEW_SIZE</span><span class="symbol">/(</span><span class="normal"><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble">gdouble</a></span><span class="symbol">)</span><span class="function"><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Standard-Macros.html#MAX:CAPS">MAX</a></span><span class="symbol">(</span><span class="function"><a href="../libgwyprocess/GwyDataField.html#gwy-data-field-get-xres">gwy_data_field_get_xres</a></span><span class="symbol">(</span><span class="normal">dfield</span><span class="symbol">),</span>
<span class="normal"> </span><span class="function"><a href="../libgwyprocess/GwyDataField.html#gwy-data-field-get-yres">gwy_data_field_get_yres</a></span><span class="symbol">(</span><span class="normal">dfield</span><span class="symbol">));</span>
<span class="function"><a href="../libgwydgets/GwyDataView.html#gwy-data-view-set-zoom">gwy_data_view_set_zoom</a></span><span class="symbol">(</span><span class="function">GWY_DATA_VIEW</span><span class="symbol">(</span><span class="normal">data_view</span><span class="symbol">),</span><span class="normal"> zoomval</span><span class="symbol">);</span>
<span class="comment">/* Pack data_view somewhere... */</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
The foregoing example uses raw data keys as <code class="literal">"/0/data"</code>.
Assuming we keep the standard naming scheme we can partially avoid this
with functions like <a href="../libgwyapp/libgwyapp-data-browser.html#gwy-app-get-data-key-for-id"><code class="function">gwy_app_get_data_key_for_id()</code></a> and
<a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Quarks.html#g-quark-to-string"><code class="function">g_quark_to_string()</code></a>. However, such helper functions do not exist for all
objects that can appear in a container therefore some knowledge of
the naming scheme is usually necessary.
</p>
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