This page details how Haiku reads keys from the keyboard including modifier key and special characters, and how you can read and process these encoded characters in your application.

Haiku and UTF-8

Haiku encodes all characters using UTF-8. UTF-8 allows Haiku to represent characters from all over the world while still maintaining backwards compatibility with 7-bit ASCII codes. This means that the most commonly used characters are encoded in just one byte while less common characters can be encoded by extending the character encoding to use two, three, or, rarely, four bytes.

Key Codes

Each key on the keyboard is assigned a numeric code to identify it to the operating system. Most of the time you should not have to access these codes directly, instead use one of the constants defined in InterfaceDefs.h such B_BACKSPACE or B_ENTER or read the character from the key_map struct.

The following diagram shows the key codes as they appear on a US 104-key keyboard.


International keyboards each differ a bit but generally share an extra key located in-between the left shift key and Z with the key code 0x69.

Mac keyboards have an equal sign in the keypad with key code 0x6a and some other differences. Often times the keys produce the same key code but appear in different locations.

Modifier Keys

Modifier keys are keys which have no effect on their own but when combined with another key modify the usual behavior of that key.

The following modifier keys are defined in InterfaceDefs.h

B_SHIFT_KEY Transforms lowercase case characters into uppercase characters or chooses alternative punctuation characters. The shift key is also used in combination with B_COMMAND_KEY to produce keyboard shortcuts.
B_COMMAND_KEY Produces keyboard shortcuts for common operations such as cut, copy, paste, print, and find.
B_CONTROL_KEY Outputs control characters in terminal. The control key is sometimes also used as an alternative to B_COMMAND_KEY to produce keyboard shortcuts in applications.
B_OPTION_KEY Used to in combination with other keys to output special characters such as accented letters and symbols. Because B_OPTION_KEY is not found on all keyboards it should not be used for essential functions.
B_MENU_KEY The Menu key is used to produce contextual menus. Like B_OPTION_KEY, the Menu key should not be used for essential functions since it is not available on all keyboards.

In addition you can access the left and right modifier keys individually with the following constants:


Scroll lock, num lock, and caps lock alter other keys pressed after they are released. They are defined by the following constants:

B_CAPS_LOCK Produces uppercase characters. Reverses the effect of B_SHIFT_KEY for letters.
B_SCROLL_LOCK Prevents the terminal from scrolling.
B_NUM_LOCK Informs the numeric keypad to output numbers when on. Reverses the function of B_SHIFT_KEY for keys on the numeric keypad.

To get the currently active modifiers use the modifiers() function defined in InterfaceDefs.h. This function returns a bitmap containing the currently active modifier keys. You can create a bit mask of the above constants to determine which modifiers are active.

Other Constants

The Interface Kit also defines constants for keys that are aren't represented by a symbol, these include:


The B_FUNCTION_KEY constant can further be broken down into the following constants:

B_F1_KEY B_F4_KEY B_F7_KEY B_F10_KEY B_PRINT_KEY (Print Screen)
B_F3_KEY B_F6_KEY B_F9_KEY B_F12_KEY B_PAUSE_KEY (Pause/Break)

For Japanese keyboard two more constants are defined:

The Keymap

The characters produced by each of the key codes is determined by the keymap. The usual way to for the user to choose and modify their keymap is the Keymap preference application. A number of alternative keymaps such as dvorak and keymaps for different locales are available.


A full description of the Keymap preflet can be found in the User Guide.

The keymap is a map of the characters produced by each key on the keyboard including the characters produced when combined with the modifier constants described above. The keymap also contains the codes of the modifier keys and tables for dead keys.

To get the current system keymap create a pointer to a key_map struct and char array and pass their addresses to the get_key_map() function. The key_map struct will be filled out with the current system keymap and the char array will be filled out with the UTF-8 character encodings.

The key_map struct contains a number of fields. Each field is described in several sections below.

The first section contains a version number and the code assigned to each of the modifier keys.

version The version number of the keymap
Lock key codes
Left and right shift key codes
Left and right command key codes
Left and right control key codes
Left and right option key codes
menu_key Menu key code
lock_settings A bitmap containing the default state of the lock keys

To programmatically set a modifier key in the system keymap use the set_modifier_key() function. You can also programmatically set the state of the num lock, caps lock, and scroll lock keys by calling the set_keyboard_locks() function.

Character Maps

The next section of the key_map struct contains maps of offsets into the array of UTF-8 character encodings filled out in the second parameter of get_key_map(). Since the character maps are filled with UTF-8 characters they may be 1, 2, 3, or rarely 4 bytes long. The characters are contained in non-NUL terminated Pascal strings. The first byte of the string indicates how many bytes the character is made up of. For example the string for a horizontal ellipses (...) character looks like this:


The first byte is 03 meaning that the character is 3 bytes long. The remaining bytes E2 80 A6 are the UTF-8 byte representation of the horizontal ellipses character. Recall that there is no terminating NUL character for these strings.

Not every key is mapped to a character. If a key is unmapped the character array contains a 0-byte string. Unmapped keys do not produce B_KEY_DOWN messages.

Modifier keys should not be mapped into the character array.

The following character maps are defined:

control_map Map of characters when the control key is pressed
option_caps_shift_map Map of characters when caps lock is turned on and both the option key and shift keys are pressed.
option_caps_map Map of characters when caps lock is turned on and the option key is pressed
option_shift_map Map of characters when both shift and option keys are pressed
option_map Map of characters when the option key is pressed
caps_shift_map Map of characters when caps lock is on and the shift key is pressed
caps_map Map of characters when caps lock is turned on
shift_map Map of characters when shift is pressed
normal_map Map of characters when no modifiers keys are pressed

Dead Keys

Dead keys are keys that do not produce a character until they are combined with another key. Because these keys do not produce a character on their own they are considered "dead" until they are "brought to life" by being combined with another key. Dead keys are generally used to produce accented characters.

Each of the fields below is a 32-byte array of dead key characters. The dead keys are organized into pairs in the array. Each dead key array can contain up to 16 pairs of dead key characters. The first pair in the array should contain B_SPACE followed by and the accent character in the second offset. This serves to identify which accent character is contained in the array and serves to define a space followed by accent pair to represent the unadorned accent character.

The rest of the array is filled with pairs containing an unaccented character followed by the accent character.

acute_dead_key Acute dead keys array
grave_dead_key Grave dead keys array
circumflex_dead_key Circumflex dead keys array
dieresis_dead_key Dieresis dead keys array
tilde_dead_key Tilde dead keys array

The final section contains bitmaps that indicate which character table is used for each of the above dead keys. The bitmap can contain any of the following constants:

The bitmaps often contain B_OPTION_TABLE because accent characters are generally produced by combining a letter with B_OPTION_KEY.

acute_tables Acute dead keys table bitmap
grave_tables Grave dead keys table bitmap
circumflex_tables Circumflex dead keys table bitmap
dieresis_tables Dieresis dead keys table bitmap
tilde_tables Tilde dead keys table bitmap