gdk-Keyboard-Handling: Key Values
Description
Functions for manipulating keyboard codesHierarchy
\link{GObject}
+----GdkKeymapDetailed Description
Key values are the codes which are sent whenever a key is pressed or released.
They appear in the keyval field of the
GdkEventKey structure, which is passed to signal handlers for the
"key-press-event" and "key-release-event" signals.
The complete list of key values can be found in the
header file. is not included in ,
it must be included independently, because the file is quite large.
Key values can be converted into a string representation using
gdkKeyvalName. The reverse function, converting a string to a key value,
is provided by gdkKeyvalFromName.
The case of key values can be determined using gdkKeyvalIsUpper and
gdkKeyvalIsLower. Key values can be converted to upper or lower case
using gdkKeyvalToUpper and gdkKeyvalToLower.
When it makes sense, key values can be converted to and from
Unicode characters with gdkKeyvalToUnicode and gdkUnicodeToKeyval.
One GdkKeymap object exists for each user display. gdkKeymapGetDefault
returns the GdkKeymap for the default display; to obtain keymaps for other
displays, use gdkKeymapGetForDisplay. A keymap
is a mapping from GdkKeymapKey to key values. You can think of a GdkKeymapKey
as a representation of a symbol printed on a physical keyboard key. That is, it
contains three pieces of information. First, it contains the hardware keycode;
this is an identifying number for a physical key. Second, it contains the
level of the key. The level indicates which symbol on the
key will be used, in a vertical direction. So on a standard US keyboard, the key
with the number "1" on it also has the exclamation point ("!") character on
it. The level indicates whether to use the "1" or the "!" symbol. The letter
keys are considered to have a lowercase letter at level 0, and an uppercase
letter at level 1, though only the uppercase letter is printed. Third, the
GdkKeymapKey contains a group; groups are not used on standard US keyboards,
but are used in many other countries. On a keyboard with groups, there can be 3
or 4 symbols printed on a single key. The group indicates movement in a
horizontal direction. Usually groups are used for two different languages. In
group 0, a key might have two English characters, and in group 1 it might have
two Hebrew characters. The Hebrew characters will be printed on the key next to
the English characters.
In order to use a keymap to interpret a key event, it's necessary to first
convert the keyboard state into an effective group and level. This is done via a
set of rules that varies widely according to type of keyboard and user
configuration. The function gdkKeymapTranslateKeyboardState accepts a
keyboard state -- consisting of hardware keycode pressed, active modifiers, and
active group -- applies the appropriate rules, and returns the group/level to be
used to index the keymap, along with the modifiers which did not affect the
group and level. i.e. it returns "unconsumed modifiers." The keyboard group may
differ from the effective group used for keymap lookups because some keys don't
have multiple groups - e.g. the Enter key is always in group 0 regardless of
keyboard state.
Note that gdkKeymapTranslateKeyboardState also returns the keyval, i.e. it
goes ahead and performs the keymap lookup in addition to telling you which
effective group/level values were used for the lookup. GdkEventKey already
contains this keyval, however, so you don't normally need to call
gdkKeymapTranslateKeyboardState just to get the keyval.References
http://developer.gnome.org/doc/API/2.0/gdk/gdk-Keyboard-Handling.html