The Be Book - Special Topics - The Keyboard
Conceptually, there are eight modifier keys. The global
modifiers()
function returns a value that encodes the current status of all eight of
these keys. You can test for the state of a particular modifier key by
comparing
modifiers()
with the constants listed in the table below. For
example, here's how you can see if the user is holding down one of the
Shift keys:
if (modifiers()|B_SHIFT_KEY) { /* a shift key is down */ }
The modifier mask is also included in the "modifiers" field in
BMessages
that report keyboard and mouse events.
How your application uses modifier keys is up to you. The list below lists the eight keys and how they're typically used.
| Constant | Description |
|---|---|
| Maps character keys to their uppercase or alternative versions. |
| In combination with a character key, performs a keyboard shortcut. |
| Turns alphabetic keys into control characters. |
| Maps keys to alternative characters, typically characters in an extended set—multibyte UTF-8 characters. |
| Pops open a menu. |
| Reverses the effect of the Shift key on alphabetic characters. |
| Reverses the effect of the Shift key on numeric characters. |
| Stops the display from scrolling. |
If you're interested in whether the left or right modifer key of a given type was pressed, you can check against these additional values:
B_LEFT_SHIFT_KEYB_RIGHT_SHIFT_KEYB_LEFT_CONTROL_KEYB_RIGHT_CONTROL_KEYB_LEFT_OPTION_KEYB_RIGHT_OPTION_KEYB_LEFT_COMMAND_KEYB_RIGHT_COMMAND_KEY
Most of the modifiers map to single, specific keys:
Shift and Caps Lock
are examples. But others don't: the Menu key maps to
Shortcut+Escape
(where Shortcut is either Alt, Command,
or Control, depending on the
user's preferences and keyboard).
