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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
	  "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">
<chapter id='Debugging_Aids'>
<title>Debugging Aids</title>

<para>
The debugging aids are intended for use primarily by Xkb implementors and are
optional in any implementation.
</para>


<para>
There are two bitmasks that may be used to control debugging. One bitmask
controls the output of debugging information, and the other controls behavior.
Both bitmasks are initially all zeros.
</para>


<para>
To change the values of any of the debug controls, use
<function>XkbSetDebuggingFlags</function>.
</para>

<indexterm significance="preferred" zone="XkbSetDebuggingFlags"><primary><function>XkbSetDebuggingFlags</function></primary></indexterm>
<funcsynopsis id="XkbSetDebuggingFlags">
  <funcprototype>
    <funcdef>Bool <function>XkbSetDebuggingFlags</function></funcdef>
<!-- (
<parameter>display, mask, flags, msg, ctrls_mask, ctrls, ret_flags, ret_ctrls</parameter>
) -->

    <paramdef>Display *<parameter>display</parameter></paramdef>
    <paramdef>unsigned int <parameter>mask</parameter></paramdef>
    <paramdef>unsigned int <parameter>flags</parameter></paramdef>
    <paramdef>char *<parameter>msg</parameter></paramdef>
    <paramdef>unsigned int <parameter>ctrls_mask</parameter></paramdef>
    <paramdef>unsigned int <parameter>ctrls</parameter></paramdef>
    <paramdef>unsigned int *<parameter>ret_flags</parameter></paramdef>
    <paramdef>unsigned int *<parameter>ret_ctrls</parameter></paramdef>
  </funcprototype>
</funcsynopsis>
<variablelist>
  <varlistentry>
    <term>
      <parameter>display</parameter>
    </term>
    <listitem>
      <para>
        connection to X server
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <parameter>mask</parameter>
    </term>
    <listitem>
      <para>
        mask selecting debug output flags to change
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <parameter>flags</parameter>
    </term>
    <listitem>
      <para>
        values for debug output flags selected by <parameter>mask</parameter>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <parameter>msg</parameter>
    </term>
    <listitem>
      <para>
        message to print right now
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <parameter>ctrls_mask</parameter>
    </term>
    <listitem>
      <para>
        mask selecting debug controls to change
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <parameter>ctrls</parameter>
    </term>
    <listitem>
      <para>
        values for debug controls selected by <parameter>ctrls_mask</parameter>
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <parameter>ret_flags</parameter>
    </term>
    <listitem>
      <para>
        resulting state of all debug output flags
      </para>
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <parameter>ret_ctrls</parameter>
    </term>
    <listitem>
      <para>
        resulting state of all debug controls
      </para>
    </listitem>
  </varlistentry>
</variablelist>

<para>
<function>XkbSetDebuggingFlags</function>
modifies the debug output flags as specified by
<parameter>mask</parameter>
and
<parameter>flags</parameter>,
modifies the debug controls flags as specified by
<parameter>ctrls_mask</parameter>
and
<parameter>ctrls</parameter>,
prints the message
<parameter>msg</parameter>,
and backfills
<parameter>ret_flags</parameter>
and
<parameter>ret_ctrls</parameter>
with the resulting debug output and debug controls flags.
</para>


<para>
When bits are set in the debug output masks,
<parameter>mask</parameter>
and
<parameter>flags</parameter>,
Xkb prints debug information corresponding to each bit at appropriate points
during its processing. The device to which the output is written is
implementation-dependent, but is normally the same device to which X server
error messages are directed; thus the bits that can be set in
<parameter>mask</parameter>
and
<parameter>flags</parameter>
is implementation-specific. To turn on a debug output selection, set the bit
for the output in the
<parameter>mask</parameter>
parameter and set the corresponding bit in the
<parameter>flags</parameter>
parameter. To turn off event selection for an event, set the bit for the
output in the
<parameter>mask</parameter>
parameter and do not set the corresponding bit in the
<parameter>flags</parameter>
parameter.
</para>


<para>
When bits are set in the debug controls masks,
<parameter>ctrls_mask</parameter>
and
<parameter>ctrls</parameter>,
Xkb modifies its behavior according to each controls bit.
<parameter>ctrls_mask</parameter>
and
<parameter>ctrls</parameter>
are related in the same way that
<parameter>mask</parameter>
and
<parameter>flags</parameter>
are. The valid controls bits are defined in
<link linkend="table22.1">Table 22.1</link>.
</para>

<table id='table22.1' frame='topbot'>
<title>Debug Control Masks</title>
<?dbfo keep-together="always" ?>
<tgroup cols='3' align='left' colsep='0' rowsep='0'>
<colspec colname='c1' colwidth='1.5*'/>
<colspec colname='c2' colwidth='1.0*'/>
<colspec colname='c3' colwidth='2.0*'/>
<thead>
<row rowsep='1'>
  <entry>Debug Control Mask</entry>
  <entry>Value</entry>
  <entry>Meaning</entry>
</row>
</thead>
<tbody>
<row>
    <entry><symbol>XkbDF_DisableLocks</symbol></entry>
    <entry>(1 &lt;&lt; 0)</entry>
    <entry>Disable actions that lock modifiers</entry>
  </row>
</tbody>
</tgroup>
</table>

<para>
<function>XkbSetDebuggingFlags</function>
returns
<symbol>True</symbol>
if successful and
<symbol>False</symbol>
otherwise. The only protocol error it may generate is
<errorname>BadAlloc</errorname>,
if for some reason it is unable to allocate storage.
</para>


<para>
<function>XkbSetDebuggingFlags</function>
is intended for developer use and may be disabled in production X servers. If
it is disabled,
<function>XkbSetDebuggingFlags</function>
has no effect and does not generate any protocol errors.
</para>


<para>
The message in
<parameter>msg</parameter>
is written immediately. The device to which it is written is implementation
dependent but is normally the same device where X server error messages are
directed.
</para>
</chapter>
