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2.4.15 Braille Display Keys

When using Braille display output, speechd-el can bind actions to the Braille display keys. The Braille key bindings are defined in the following variables:

speechd-braille-key-functions

Alist of Braille display key codes and corresponding Emacs functions. If the given key is pressed, the corresponding function is called with a speechd-brltty-driver instance as its single argument (read the source code for information about speechd-el output drivers).

The key codes are either integers (for BRLTTY 3.7 and older) or lists containing three integers (for BRLTTY 3.8 and newer). See the default variable value for examples of possible key codes.

The assigned functions needn’t be interactive. Actually as the functions may be invoked by asynchronous events any time at any place, they shouldn’t modify current environment in any inappropriate way. For this reason it is recommended not to assign user commands to the keys here.

speechd-brltty.el contains some predefined functions that can be assigned to the Braille display keys here:

speechd-brltty-scroll-left

Scroll towards the beginning of the currently displayed message.

speechd-brltty-scroll-right

Scroll towards the end of the currently displayed message.

speechd-brltty-scroll-to-bol

Scroll to the beginning of the currently displayed message.

speechd-brltty-scroll-to-eol

Scroll to the end of the currently displayed message.

speechd-brltty-scroll-to-cursor

Scroll to the cursor position (if any) in the displayed message.

speechd-brltty-finish-message

Stop displaying the current message and display the next one.

speechd-brltty-cancel

Stop displaying the current message and discard all messages waiting in the queue.

speechd-brltty-previous-message

Display the previous message from the history.

speechd-brltty-next-message

Display the next message from the history.

speechd-brltty-first-message

Display the first message in the history.

speechd-brltty-last-message

Display the last message in the history.

Additionally, the following macro is provided:

speechd-brltty-command-key-function key

Insert function for handling key as a general input key. This is useful for handling Braille keys acting as general character input keys.

The speechd-braille-key-functions variable contains some default bindings initially, but as the keys and their codes differ a lot for various Braille displays, you probably need to adjust it for your particular device. You can figure out the display key codes by setting the speechd-braille-show-unknown-keys variable to t and pressing the display keys.

speechd-braille-show-unknown-keys

If non-nil, show codes of the pressed Braille keys that have no function assigned in speechd-braille-key-functions. This is useful to figure out the Braille key codes.

With BrlTTY 3.8 and higher BrlTTY can handle many braille keys itself in X environment. So speechd-el doesn’t try to handle most keys itself by default. Instead it handles only keys assigned in speechd-braille-key-functions. If this is a problem, typically when looking for braille key codes, the following command can be useful:

C-e C-b k

Toggle handling braille keys by speechd-el. If BrlTTY handles the keys (this is the default behavior), speechd-el receives only keys which are assigned to commands in speechd-braille-key-functions. If speechd-el handles the keys, then BrlTTY sends all the pressed keys to speechd-el without processing them itself.


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