5 This document contains a quick walk-through of the often-used parts of
6 the library. We will employ a few use-cases to lead the examples:
8 1. An evdev client. "evdev" is the Linux kernel's input subsystem; it
9 only reports to the client which keys are pressed and released.
11 2. An X11 client, using the XCB library to communicate with the X
12 server and the xcb-xkb library for using the XKB protocol.
14 3. A Wayland client, using the standard protocol.
16 The snippets are not complete, and some support code is omitted. You
17 can find complete and more complex examples in the source directory:
19 1. test/interactive-evdev.c contains an interactive evdev client.
21 2. test/interactive-x11.c contains an interactive X11 client.
23 Also, the library contains many more functions for examining and using
24 the library context, the keymap and the keyboard state. See the
25 hyper-linked reference documentation or go through the header files in
26 xkbcommon/ for more details.
30 Before we can do anything interesting, we need a library context. So
34 #include <xkbcommon/xkbcommon.h>
36 struct xkb_context ctx;
38 ctx = xkb_context_new(XKB_CONTEXT_NO_FLAGS);
42 The xkb_context contains the keymap include paths, the log level and
43 functions, and other general customizable administrativia.
45 Next we need to create a keymap, xkb_keymap. There are different ways to
48 If we are an evdev client, we have nothing to go by, so we need to ask
49 the user for his/her keymap preferences (for example, an Icelandic
50 keyboard with a Dvorak layout). The configuration format is commonly
51 called RMLVO (Rules+Model+Layout+Variant+Options), the same format used
52 by the X server. With it, we can fill a struct called xkb_rule_names;
53 passing NULL chooses the system's default.
56 struct xkb_keymap *keymap;
57 struct xkb_rule_names names = <...>;
59 keymap = xkb_keymap_new_from_names(ctx, &names,
60 XKB_KEYMAP_COMPILE_NO_FLAGS);
64 If we are a Wayland client, the compositor gives us a string complete
65 with a keymap. In this case, we can create the keymap object like this:
68 const char *keymap_string = <...>;
70 keymap = xkb_keymap_new_from_string(ctx, keymap_string,
71 XKB_KEYMAP_FORMAT_TEXT_V1,
72 XKB_KEYMAP_COMPILE_NO_FLAGS);
76 If we are an X11 client, we are better off getting the keymap from the
77 X server directly. For this we need to choose the XInput device; here
78 we will use the core keyboard device:
81 #include <xkbcommon/xkbcommon-x11.h>
83 xcb_connection_t *conn = <...>;
86 device_id = xkb_x11_get_core_keyboard_device_id(conn);
87 if (device_id == -1) <error>
89 keymap = xkb_x11_keymap_new_from_device(ctx, conn, device_id,
90 XKB_KEYMAP_COMPILE_NO_FLAGS);
94 Now that we have the keymap, we are ready to handle the keyboard devices.
95 For each device, we create an xkb_state:
98 struct xkb_state *state;
100 state = xkb_state_new(keymap);
104 For X11/XCB clients, this is better:
107 state = xkb_x11_state_new_from_device(keymap, conn, device_id);
111 When we have an xkb_state for a device, we can start handling key events
112 from it. Given a keycode for a key, we can get its keysym:
115 <key event structure> event;
116 xkb_keycode_t keycode;
119 keycode = event->keycode;
120 keysym = xkb_state_key_get_one_sym(state, keycode);
123 We can see which keysym we got, and get its name:
126 char[64] keysym_name;
128 if (keysym == XKB_KEY_Space)
131 xkb_keysym_get_name(keysym, keysym_name, sizeof(keysym_name));
134 libxkbcommon also supports an extension to the classic XKB, whereby a
135 single event can result in multiple keysyms. Here's how to use it:
138 const xkb_keysym_t *keysyms;
141 num_keysyms = xkb_state_key_get_syms(state, keycode);
144 We can also get a UTF-8 string representation for this key:
150 // First find the needed size; return value is the same as snprintf(3).
151 size = xkb_state_key_get_utf8(state, keycode, NULL, 0) + 1;
152 if (size <= 1) <nothing to do>
153 buffer = <allocate size bytes>
155 xkb_state_key_get_utf8(state, keycode, buffer, size);
158 Of course, we also need to keep the xkb_state up-to-date with the
159 keyboard device, if we want to get the correct keysyms in the future.
161 If we are an evdev client, we must let the library know whether a key
162 is pressed or released at any given time:
165 enum xkb_state_component changed;
168 changed = xkb_state_update_key(state, keycode, XKB_KEY_DOWN);
169 else if (<key release>)
170 changed = xkb_state_update_key(state, keycode, XKB_KEY_UP);
173 The `changed` return value tells us exactly which parts of the state
176 If is is a key-repeat event, we can ask the keymap what to do with it:
179 if (<key repeat> && !xkb_keymap_key_repeats(keymap, keycode))
183 On the other hand, if we are an X or Wayland client, the server already
184 does the hard work for us. It notifies us when the device's state
185 changes, and we can simply use what it tells us (the necessary
186 information usually comes in a form of some "state changed" event):
189 changed = xkb_state_update_mask(state,
190 event->depressed_mods,
193 event->depressed_layout,
194 event->latched_layout,
195 event->locked_layout);
198 Now that we have an always-up-to-date xkb_state, we can examine it.
199 For example, we can check whether the Control modifier is active, or
200 whether the Num Lock LED is active:
203 if (xkb_state_mod_name_is_active(state, XKB_MOD_NAME_CTRL,
204 XKB_STATE_MODS_EFFECTIVE) > 0)
205 <The Control modifier is active>
207 if (xkb_state_led_name_is_active(state, XKB_LED_NAME_NUM) > 0)
208 <The Num Lock LED is active>
211 And that's it! When we're finished, we should free the objects we've
215 xkb_state_unref(state);
216 xkb_keymap_unref(keymap);
217 xkb_context_unref(ctx);