diff options
Diffstat (limited to 'specs/ch05.xml')
| -rw-r--r-- | specs/ch05.xml | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/specs/ch05.xml b/specs/ch05.xml new file mode 100644 index 0000000..d00a26d --- /dev/null +++ b/specs/ch05.xml @@ -0,0 +1,88 @@ + +<chapter id='key_event_processing_overview'> +<title>Key Event Processing Overview</title> + +<para> +There are three steps to processing each key event in the X server, and at +least three in the client. This section describes each of these steps briefly; +the following sections describe each step in more detail. +</para> + +<orderedlist> +<listitem> + <para>First, the server applies global keyboard controls to determine whether +the key event should be processed immediately, deferred, or ignored. For +example, the <emphasis> +SlowKeys</emphasis> + control can cause a key event to be deferred until the slow keys delay has +elapsed while the <emphasis> +RepeatKeys</emphasis> + control can cause multiple X events from a single physical key press if the +key is held down for an extended period. The global keyboard controls affect +all of the keys on the keyboard and are described in <ulink +url="XKBproto.htm#50332257_28742">See Global Keyboard Controls</ulink>. + </para> +</listitem> +<listitem> + <para>Next, the server applies per-key behavior. Per key-behavior can be used +to simulate or indicate some special kinds of key behavior. For example, +keyboard overlays, in which a key generates an alternate keycode under certain +circumstances, can be implemented using per-key behavior. Every key has a +single behavior, so the effect of key behavior does not depend on keyboard +modifier or group state, though it might depend on global keyboard controls. +Per-key behaviors are described in detail in <ulink +url="XKBproto.htm#50332257_81140">See Key Behavior</ulink>. + </para> +</listitem> +<listitem> + <para>Finally, the server applies key actions. Logically, every keysym on the +keyboard has some action associated with it. The key action tells the server +what to do when an event which yields the corresponding keysym is generated. +Key actions might change or suppress the event, generate some other event, or +change some aspect of the server. Key actions are described in <ulink +url="XKBproto.htm#50332257_15763">See Key Actions</ulink>. + </para> +</listitem> +</orderedlist> + +<para> +If the global controls, per-key behavior and key action combine to cause a key +event, the client which receives the event processes it in several steps. +</para> + +<orderedlist> +<listitem> + <para>First the client extracts the effective keyboard group and a set of +modifiers from the state field of the event. See <ulink +url="XKBproto.htm#50332257_90933">See Computing A State Field from an XKB +State</ulink> for details. + </para> +</listitem> +<listitem> + <para>Using the modifiers and effective keyboard group, the client selects a +symbol from the list of keysyms bound to the key. <ulink +url="XKBproto.htm#50332257_24122">See Determining the KeySym Associated with a +Key Event</ulink> discusses symbol selection. + </para> +</listitem> +<listitem> + <para>If necessary, the client transforms the symbol and resulting string +using any modifiers that are "left over" from the process of looking up a +symbol. For example, if the <emphasis> +Lock</emphasis> + modifier is left over, the resulting keysym is capitalized according to the +capitalization rules specified by the system. See <ulink +url="XKBproto.htm#50332257_25094">See Transforming the KeySym Associated with a +Key Event</ulink> for a more detailed discussion of the transformations defined +by XKB. + </para> +</listitem> +<listitem> + <para>Finally, the client uses the keysym and remaining modifiers in an +application-specific way. For example, applications based on the X toolkit +might apply translations based on the symbol and modifiers reported by the +first three steps. + </para> +</listitem> +</orderedlist> +</chapter> |