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:
33 #include <xkbcommon/xkbcommon.h>
35 struct xkb_context ctx;
37 ctx = xkb_context_new(XKB_CONTEXT_NO_FLAGS);
41 The `xkb_context` contains the keymap include paths, the log level and
42 functions, and other general customizable administrativia.
44 Next we need to create a keymap, `xkb_keymap`. This is an immutable object
45 which contains all of the information about the keys, layouts, etc. There
46 are different ways to do this.
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 /* Example RMLVO for Icelandic Dvorak. */
58 struct xkb_rule_names names = {
63 .options = "terminate:ctrl_alt_bksp"
66 keymap = xkb_keymap_new_from_names(ctx, &names,
67 XKB_KEYMAP_COMPILE_NO_FLAGS);
71 If we are a Wayland client, the compositor gives us a string complete
72 with a keymap. In this case, we can create the keymap object like this:
75 /* From the wl_keyboard::keymap event. */
76 const char *keymap_string = <...>;
78 keymap = xkb_keymap_new_from_string(ctx, keymap_string,
79 XKB_KEYMAP_FORMAT_TEXT_V1,
80 XKB_KEYMAP_COMPILE_NO_FLAGS);
84 If we are an X11 client, we are better off getting the keymap from the
85 X server directly. For this we need to choose the XInput device; here
86 we will use the core keyboard device:
89 #include <xkbcommon/xkbcommon-x11.h>
91 xcb_connection_t *conn = <...>;
94 device_id = xkb_x11_get_core_keyboard_device_id(conn);
95 if (device_id == -1) <error>
97 keymap = xkb_x11_keymap_new_from_device(ctx, conn, device_id,
98 XKB_KEYMAP_COMPILE_NO_FLAGS);
102 Now that we have the keymap, we are ready to handle the keyboard devices.
103 For each device, we create an `xkb_state`, which remembers things like which
104 keyboard modifiers and LEDs are active:
107 struct xkb_state *state;
109 state = xkb_state_new(keymap);
113 For X11/XCB clients, this is better:
116 state = xkb_x11_state_new_from_device(keymap, conn, device_id);
120 When we have an `xkb_state` for a device, we can start handling key events
121 from it. Given a keycode for a key, we can get its keysym:
124 <key event structure> event;
125 xkb_keycode_t keycode;
128 keycode = event->keycode;
129 keysym = xkb_state_key_get_one_sym(state, keycode);
132 We can see which keysym we got, and get its name:
135 char keysym_name[64];
137 if (keysym == XKB_KEY_Space)
140 xkb_keysym_get_name(keysym, keysym_name, sizeof(keysym_name));
143 libxkbcommon also supports an extension to the classic XKB, whereby a
144 single event can result in multiple keysyms. Here's how to use it:
147 const xkb_keysym_t *keysyms;
150 num_keysyms = xkb_state_key_get_syms(state, keycode, &keysyms);
153 We can also get a UTF-8 string representation for this key:
159 // First find the needed size; return value is the same as snprintf(3).
160 size = xkb_state_key_get_utf8(state, keycode, NULL, 0) + 1;
161 if (size <= 1) <nothing to do>
162 buffer = <allocate size bytes>
164 xkb_state_key_get_utf8(state, keycode, buffer, size);
167 Of course, we also need to keep the `xkb_state` up-to-date with the
168 keyboard device, if we want to get the correct keysyms in the future.
170 If we are an evdev client, we must let the library know whether a key
171 is pressed or released at any given time:
174 enum xkb_state_component changed;
177 changed = xkb_state_update_key(state, keycode, XKB_KEY_DOWN);
178 else if (<key release>)
179 changed = xkb_state_update_key(state, keycode, XKB_KEY_UP);
182 The `changed` return value tells us exactly which parts of the state
185 If it is a key-repeat event, we can ask the keymap what to do with it:
188 if (<key repeat> && !xkb_keymap_key_repeats(keymap, keycode))
192 On the other hand, if we are an X or Wayland client, the server already
193 does the hard work for us. It notifies us when the device's state
194 changes, and we can simply use what it tells us (the necessary
195 information usually comes in a form of some "state changed" event):
198 changed = xkb_state_update_mask(state,
199 event->depressed_mods,
202 event->depressed_layout,
203 event->latched_layout,
204 event->locked_layout);
207 Now that we have an always-up-to-date `xkb_state`, we can examine it.
208 For example, we can check whether the Control modifier is active, or
209 whether the Num Lock LED is active:
212 if (xkb_state_mod_name_is_active(state, XKB_MOD_NAME_CTRL,
213 XKB_STATE_MODS_EFFECTIVE) > 0)
214 <The Control modifier is active>
216 if (xkb_state_led_name_is_active(state, XKB_LED_NAME_NUM) > 0)
217 <The Num Lock LED is active>
220 And that's it! Eventually, we should free the objects we've created:
223 xkb_state_unref(state);
224 xkb_keymap_unref(keymap);
225 xkb_context_unref(ctx);