87 lines
3.6 KiB
XML
87 lines
3.6 KiB
XML
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<chapter id='Key_Event_Processing_Overview'>
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<title>Key Event Processing Overview</title>
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<para>
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There are three steps to processing each key event in the X server, and at
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least three in the client. This section describes each of these steps briefly;
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the following sections describe each step in more detail.
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</para>
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<orderedlist>
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<listitem>
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<para>First, the server applies global keyboard controls to determine whether
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the key event should be processed immediately, deferred, or ignored. For
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example, the <emphasis>
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SlowKeys</emphasis>
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control can cause a key event to be deferred until the slow keys delay has
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elapsed while the <emphasis>
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RepeatKeys</emphasis>
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control can cause multiple X events from a single physical key press if the
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key is held down for an extended period. The global keyboard controls affect
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all of the keys on the keyboard and are described in
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<link linkend='Global_Keyboard_Controls'>Global Keyboard Controls</link>.
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</para>
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</listitem>
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<listitem>
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<para>Next, the server applies per-key behavior. Per key-behavior can be used
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to simulate or indicate some special kinds of key behavior. For example,
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keyboard overlays, in which a key generates an alternate keycode under certain
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circumstances, can be implemented using per-key behavior. Every key has a
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single behavior, so the effect of key behavior does not depend on keyboard
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modifier or group state, though it might depend on global keyboard controls.
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Per-key behaviors are described in detail in
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<link linkend='Key_Behavior'>Key Behavior</link>.
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</para>
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</listitem>
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<listitem>
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<para>Finally, the server applies key actions. Logically, every keysym on the
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keyboard has some action associated with it. The key action tells the server
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what to do when an event which yields the corresponding keysym is generated.
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Key actions might change or suppress the event, generate some other event, or
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change some aspect of the server. Key actions are described in <link linkend='Key_Actions'>Key Actions</link>.
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</para>
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</listitem>
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</orderedlist>
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<para>
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If the global controls, per-key behavior and key action combine to cause a key
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event, the client which receives the event processes it in several steps.
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</para>
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<orderedlist>
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<listitem>
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<para>First the client extracts the effective keyboard group and a set of
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modifiers from the state field of the event. See <link linkend='Computing_A_State_Field_from_an_XKB_State'>Computing A State Field from an XKB
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State</link> for details.
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</para>
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</listitem>
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<listitem>
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<para>Using the modifiers and effective keyboard group, the client selects a
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symbol from the list of keysyms bound to the key. <link linkend='Determining_the_KeySym_Associated_with_a_Key_Event'>Determining the KeySym Associated with a
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Key Event</link> discusses symbol selection.
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</para>
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</listitem>
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<listitem>
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<para>If necessary, the client transforms the symbol and resulting string
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using any modifiers that are "left over" from the process of looking up a
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symbol. For example, if the <emphasis>
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Lock</emphasis>
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modifier is left over, the resulting keysym is capitalized according to the
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capitalization rules specified by the system. See
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<link linkend='Transforming_the_KeySym_Associated_with_a_Key_Event'>
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Transforming the KeySym Associated with a
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Key Event</link> for a more detailed discussion of the transformations defined
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by XKB.
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</para>
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</listitem>
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<listitem>
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<para>Finally, the client uses the keysym and remaining modifiers in an
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application-specific way. For example, applications based on the X toolkit
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might apply translations based on the symbol and modifiers reported by the
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first three steps.
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</para>
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</listitem>
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</orderedlist>
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</chapter>
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