95 lines
3.1 KiB
XML
95 lines
3.1 KiB
XML
<chapter id='Replacing_the_Keyboard_On_the_Fly'>
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<title>Replacing the Keyboard "On-the-Fly"</title>
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<para>
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XKB supports the <emphasis>
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XkbNewKeyboardNotify</emphasis>
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event, which reports a change in keyboard geometry or the range of supported
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keycodes. The server can generate an <emphasis>
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XkbNewKeyboardNotify</emphasis>
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event when it detects a new keyboard, or in response to an <emphasis>
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XkbGetKeyboardByName</emphasis>
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request (see <link linkend='Using_the_Servers_Database_of_Keyboard_Components'>Using the Server’s
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Database of Keyboard Components</link>) which loads a new keyboard description.
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</para>
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<para>
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When a client opens a connection to the X server, the server reports the
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minimum and maximum keycodes. If the range of supported keycodes is changed,
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XKB keeps track of the minimum and maximum keycodes that were reported to each
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client and filters out any events that fall outside of that range. Note that
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these events are simply ignored; they are not delivered to some other client.
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</para>
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<para>
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When the server sends an <emphasis>
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XkbNewKeyboardNotify</emphasis>
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event to a client to inform it of the new keycode range, XKB resets the stored
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range of legal keycodes to the keycode range reported in the event. Non-XKB
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clients and XKB-aware clients that do not request <emphasis>
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XkbNewKeyboardNotify</emphasis>
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events never receive events from keys that fall outside of the legal range
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that XKB maintains for that client.
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</para>
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<para>
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When a client requests <emphasis>
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XkbNewKeyboardNotify</emphasis>
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events, the server compares the range of keycodes for the current keyboard to
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the range of keycodes that are valid for the client. If they are not the same,
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the server immediately sends that client an <emphasis>
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XkbNewKeyboardNotify</emphasis>
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event. Even if the "new" keyboard is not new to the server, it is new to this
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particular client.
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</para>
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<para>
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In addition to filtering out-of-range key events, XKB:
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</para>
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<itemizedlist>
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<listitem>
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<para>Adjusts core protocol <emphasis>
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MappingNotify</emphasis>
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events to refer only to keys that match the stored legal range.
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</para>
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</listitem>
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<listitem>
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<para>Reports keyboard mappings for keys that match the stored legal range to
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clients that issue a core protocol <emphasis>
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GetKeyboardMapping</emphasis>
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request.
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</para>
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</listitem>
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<listitem>
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<para>Reports modifier mappings only for keys that match the stored legal
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range to clients that issue a core protocol <emphasis>
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GetModifierMapping</emphasis>
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request.
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</para>
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</listitem>
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<listitem>
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<para>Restricts the core protocol <emphasis>
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ChangeKeyboardMapping</emphasis>
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and <emphasis>
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SetModifierMapping</emphasis>
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requests to keys that fall inside the stored legal range.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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In short, XKB does everything possible to hide the fact that the range of legal
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keycodes has changed from clients non-XKB clients, which cannot be expected to
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deal with it. The corresponding XKB events and requests do <emphasis>
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not</emphasis>
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pay attention to the legal keycode range in the same way because XKB makes it
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possible for clients to track changes to the keycode range for a device and
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respond to them.
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</para>
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</chapter>
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