1 # Quick Guide 2 3 ## Introduction 4 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: 7 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. 10 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. 13 14 3. A Wayland client, using the standard protocol. 15 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: 18 19 1. test/interactive-evdev.c contains an interactive evdev client. 20 21 2. test/interactive-x11.c contains an interactive X11 client. 22 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. 27 28 ## Code 29 30 Before we can do anything interesting, we need a library context. So 31 let's create one: 32 33 ~~~{.c} 34 #include <xkbcommon/xkbcommon.h> 35 36 struct xkb_context ctx; 37 38 ctx = xkb_context_new(XKB_CONTEXT_NO_FLAGS); 39 if (!ctx) <error> 40 ~~~ 41 42 The xkb_context contains the keymap include paths, the log level and 43 functions, and other general customizable administrativia. 44 45 Next we need to create a keymap, xkb_keymap. This is an immutable object 46 which contains all of the information about the keys, layouts, etc. There 47 are different ways to do this. 48 49 If we are an evdev client, we have nothing to go by, so we need to ask 50 the user for his/her keymap preferences (for example, an Icelandic 51 keyboard with a Dvorak layout). The configuration format is commonly 52 called RMLVO (Rules+Model+Layout+Variant+Options), the same format used 53 by the X server. With it, we can fill a struct called xkb_rule_names; 54 passing NULL chooses the system's default. 55 56 ~~~{.c} 57 struct xkb_keymap *keymap; 58 /* Example RMLVO for Icelandic Dvorak. */ 59 struct xkb_rule_names names = { 60 .rules = NULL, 61 .model = "pc105", 62 .layout = "is", 63 .variant = "dvorak", 64 .options = "terminate:ctrl_alt_bksp" 65 }; 66 67 keymap = xkb_keymap_new_from_names(ctx, &names, 68 XKB_KEYMAP_COMPILE_NO_FLAGS); 69 if (!keymap) <error> 70 ~~~ 71 72 If we are a Wayland client, the compositor gives us a string complete 73 with a keymap. In this case, we can create the keymap object like this: 74 75 ~~~{.c} 76 /* From the wl_keyboard::keymap event. */ 77 const char *keymap_string = <...>; 78 79 keymap = xkb_keymap_new_from_string(ctx, keymap_string, 80 XKB_KEYMAP_FORMAT_TEXT_V1, 81 XKB_KEYMAP_COMPILE_NO_FLAGS); 82 if (!keymap) <error> 83 ~~~ 84 85 If we are an X11 client, we are better off getting the keymap from the 86 X server directly. For this we need to choose the XInput device; here 87 we will use the core keyboard device: 88 89 ~~~{.c} 90 #include <xkbcommon/xkbcommon-x11.h> 91 92 xcb_connection_t *conn = <...>; 93 int32_t device_id; 94 95 device_id = xkb_x11_get_core_keyboard_device_id(conn); 96 if (device_id == -1) <error> 97 98 keymap = xkb_x11_keymap_new_from_device(ctx, conn, device_id, 99 XKB_KEYMAP_COMPILE_NO_FLAGS); 100 if (!keymap) <error> 101 ~~~ 102 103 Now that we have the keymap, we are ready to handle the keyboard devices. 104 For each device, we create an xkb_state, which remembers things like which 105 keyboard modifiers and LEDs are active: 106 107 ~~~{.c} 108 struct xkb_state *state; 109 110 state = xkb_state_new(keymap); 111 if (!state) <error> 112 ~~~ 113 114 For X11/XCB clients, this is better: 115 116 ~~~{.c} 117 state = xkb_x11_state_new_from_device(keymap, conn, device_id); 118 if (!state) <error> 119 ~~~ 120 121 When we have an xkb_state for a device, we can start handling key events 122 from it. Given a keycode for a key, we can get its keysym: 123 124 ~~~{.c} 125 <key event structure> event; 126 xkb_keycode_t keycode; 127 xkb_keysym_t keysym; 128 129 keycode = event->keycode; 130 keysym = xkb_state_key_get_one_sym(state, keycode); 131 ~~~ 132 133 We can see which keysym we got, and get its name: 134 135 ~~~{.c} 136 char keysym_name[64]; 137 138 if (keysym == XKB_KEY_Space) 139 <got a space> 140 141 xkb_keysym_get_name(keysym, keysym_name, sizeof(keysym_name)); 142 ~~~ 143 144 libxkbcommon also supports an extension to the classic XKB, whereby a 145 single event can result in multiple keysyms. Here's how to use it: 146 147 ~~~{.c} 148 const xkb_keysym_t *keysyms; 149 int num_keysyms; 150 151 num_keysyms = xkb_state_key_get_syms(state, keycode, &keysyms); 152 ~~~ 153 154 We can also get a UTF-8 string representation for this key: 155 156 ~~~{.c} 157 char *buffer; 158 int size; 159 160 // First find the needed size; return value is the same as snprintf(3). 161 size = xkb_state_key_get_utf8(state, keycode, NULL, 0) + 1; 162 if (size <= 1) <nothing to do> 163 buffer = <allocate size bytes> 164 165 xkb_state_key_get_utf8(state, keycode, buffer, size); 166 ~~~ 167 168 Of course, we also need to keep the xkb_state up-to-date with the 169 keyboard device, if we want to get the correct keysyms in the future. 170 171 If we are an evdev client, we must let the library know whether a key 172 is pressed or released at any given time: 173 174 ~~~{.c} 175 enum xkb_state_component changed; 176 177 if (<key press>) 178 changed = xkb_state_update_key(state, keycode, XKB_KEY_DOWN); 179 else if (<key release>) 180 changed = xkb_state_update_key(state, keycode, XKB_KEY_UP); 181 ~~~ 182 183 The `changed` return value tells us exactly which parts of the state 184 have changed. 185 186 If is is a key-repeat event, we can ask the keymap what to do with it: 187 188 ~~~{.c} 189 if (<key repeat> && !xkb_keymap_key_repeats(keymap, keycode)) 190 <discard event> 191 ~~~ 192 193 On the other hand, if we are an X or Wayland client, the server already 194 does the hard work for us. It notifies us when the device's state 195 changes, and we can simply use what it tells us (the necessary 196 information usually comes in a form of some "state changed" event): 197 198 ~~~{.c} 199 changed = xkb_state_update_mask(state, 200 event->depressed_mods, 201 event->latched_mods, 202 event->locked_mods, 203 event->depressed_layout, 204 event->latched_layout, 205 event->locked_layout); 206 ~~~ 207 208 Now that we have an always-up-to-date xkb_state, we can examine it. 209 For example, we can check whether the Control modifier is active, or 210 whether the Num Lock LED is active: 211 212 ~~~{.c} 213 if (xkb_state_mod_name_is_active(state, XKB_MOD_NAME_CTRL, 214 XKB_STATE_MODS_EFFECTIVE) > 0) 215 <The Control modifier is active> 216 217 if (xkb_state_led_name_is_active(state, XKB_LED_NAME_NUM) > 0) 218 <The Num Lock LED is active> 219 ~~~ 220 221 And that's it! When we're finished, we should free the objects we've 222 created: 223 224 ~~~{.c} 225 xkb_state_unref(state); 226 xkb_keymap_unref(keymap); 227 xkb_context_unref(ctx); 228 ~~~ 229
