Reading key presses

How to read key presses from the braille terminal. More...

Data Structures
struct	brlapi_expandedKeyCode_t
struct	brlapi_describedKeyCode_t
struct	brlapi_range_t

Macros
#define	brlapi_ignoreAllKeys()   brlapi_ignoreKeys(brlapi_rangeType_all, NULL, 0)
#define	brlapi_acceptAllKeys()   brlapi_acceptKeys(brlapi_rangeType_all, NULL, 0)
#define	BRLAPI_UC_ROW   0x2800UL
#define	brlapi__ignoreAllKeys(handle)   brlapi__ignoreKeys(handle, brlapi_rangeType_all, NULL, 0)
#define	brlapi__acceptAllKeys(handle)   brlapi__acceptKeys(handle, brlapi_rangeType_all, NULL, 0)

Enumerations
enum	brlapi_rangeType_t {   brlapi_rangeType_all , brlapi_rangeType_type , brlapi_rangeType_command , brlapi_rangeType_key ,   brlapi_rangeType_code }

Functions
int BRLAPI_STDCALL	brlapi_expandKeyCode (brlapi_keyCode_t code, brlapi_expandedKeyCode_t *expansion)
int BRLAPI_STDCALL	brlapi_describeKeyCode (brlapi_keyCode_t code, brlapi_describedKeyCode_t *description)
int BRLAPI_STDCALL	brlapi_readKey (int wait, brlapi_keyCode_t *code)
int BRLAPI_STDCALL	brlapi__readKey (brlapi_handle_t *handle, int wait, brlapi_keyCode_t *code)
int BRLAPI_STDCALL	brlapi_readKeyWithTimeout (int timeout_ms, brlapi_keyCode_t *code)
int BRLAPI_STDCALL	brlapi__readKeyWithTimeout (brlapi_handle_t *handle, int timeout_ms, brlapi_keyCode_t *code)
int BRLAPI_STDCALL	brlapi_ignoreKeys (brlapi_rangeType_t type, const brlapi_keyCode_t keys[], unsigned int count)
int BRLAPI_STDCALL	brlapi__ignoreKeys (brlapi_handle_t *handle, brlapi_rangeType_t type, const brlapi_keyCode_t keys[], unsigned int count)
int BRLAPI_STDCALL	brlapi_acceptKeys (brlapi_rangeType_t type, const brlapi_keyCode_t keys[], unsigned int count)
int BRLAPI_STDCALL	brlapi__acceptKeys (brlapi_handle_t *handle, brlapi_rangeType_t type, const brlapi_keyCode_t keys[], unsigned int count)
int BRLAPI_STDCALL	brlapi__ignoreAllKeys (brlapi_handle_t *handle)
int BRLAPI_STDCALL	brlapi__acceptAllKeys (brlapi_handle_t *handle)
int BRLAPI_STDCALL	brlapi_ignoreKeyRanges (const brlapi_range_t ranges[], unsigned int count)
int BRLAPI_STDCALL	brlapi__ignoreKeyRanges (brlapi_handle_t *handle, const brlapi_range_t ranges[], unsigned int count)
int BRLAPI_STDCALL	brlapi_acceptKeyRanges (const brlapi_range_t ranges[], unsigned int count)
int BRLAPI_STDCALL	brlapi__acceptKeyRanges (brlapi_handle_t *handle, const brlapi_range_t ranges[], unsigned int count)

Detailed Description

Once brlapi_enterTtyMode() has been called, the application can call brlapi_readKey() to read key presses. Either key codes (see Types and Defines forBrlAPI Key Codes) or commands will be returned, depending on parameters given to brlapi_enterTtyMode().

Key presses are buffered, so that calling brlapi_readKey() in non-blocking mode from time to time should suffice.

Macro Definition Documentation

brlapi__acceptAllKeys

#define brlapi__acceptAllKeys

(

handle

)

brlapi__acceptKeys(handle, brlapi_rangeType_all, NULL, 0)

brlapi__ignoreAllKeys

#define brlapi__ignoreAllKeys

(

handle

)

brlapi__ignoreKeys(handle, brlapi_rangeType_all, NULL, 0)

brlapi_acceptAllKeys

int BRLAPI_STDCALL brlapi_acceptAllKeys

(

void

)

brlapi_acceptKeys(brlapi_rangeType_all, NULL, 0)

Accept all key presses from the braille keyboard

This function asks the server to give all keys to the application, and not give them to brltty.

Warning: after calling this function, make sure to call brlapi_ignoreKeys() for ignoring important keys like BRL_CMD_SWITCHVT_PREV/NEXT and such.

The sets of such keys are reset on brlapi_enterTtyMode call.

brlapi_ignoreAllKeys

int BRLAPI_STDCALL brlapi_ignoreAllKeys

(

void

)

brlapi_ignoreKeys(brlapi_rangeType_all, NULL, 0)

Ignore all key presses from the braille keyboard

This function asks the server to give all keys to brltty, rather than returning them to the application via brlapi_readKey().

The sets of such keys are reset on brlapi_enterTtyMode call.

BRLAPI_UC_ROW

#define BRLAPI_UC_ROW   0x2800UL

Unicode braille row

Enumeration Type Documentation

brlapi_rangeType_t

enum brlapi_rangeType_t

types of key ranges

Enumerator
brlapi_rangeType_all	all keys, code must be 0
brlapi_rangeType_type	all keys of a given type
brlapi_rangeType_command	all keys of a given command block, i.e. matching the key type and command parts
brlapi_rangeType_key	a given key with any flags
brlapi_rangeType_code	a given key code

Function Documentation

brlapi__acceptAllKeys()

int BRLAPI_STDCALL brlapi__acceptAllKeys

(

brlapi_handle_t *

handle

)

brlapi__acceptKeyRanges()

int BRLAPI_STDCALL brlapi__acceptKeyRanges	(	brlapi_handle_t *	handle,
		const brlapi_range_t	ranges[],
		unsigned int	count
	)

brlapi__acceptKeys()

int BRLAPI_STDCALL brlapi__acceptKeys	(	brlapi_handle_t *	handle,
		brlapi_rangeType_t	type,
		const brlapi_keyCode_t	keys[],
		unsigned int	count
	)

brlapi__ignoreAllKeys()

int BRLAPI_STDCALL brlapi__ignoreAllKeys

(

brlapi_handle_t *

handle

)

brlapi__ignoreKeyRanges()

int BRLAPI_STDCALL brlapi__ignoreKeyRanges	(	brlapi_handle_t *	handle,
		const brlapi_range_t	ranges[],
		unsigned int	count
	)

brlapi__ignoreKeys()

int BRLAPI_STDCALL brlapi__ignoreKeys	(	brlapi_handle_t *	handle,
		brlapi_rangeType_t	type,
		const brlapi_keyCode_t	keys[],
		unsigned int	count
	)

brlapi__readKey()

int BRLAPI_STDCALL brlapi__readKey	(	brlapi_handle_t *	handle,
		int	wait,
		brlapi_keyCode_t *	code
	)

brlapi__readKeyWithTimeout()

int BRLAPI_STDCALL brlapi__readKeyWithTimeout	(	brlapi_handle_t *	handle,
		int	timeout_ms,
		brlapi_keyCode_t *	code
	)

brlapi_acceptKeyRanges()

int BRLAPI_STDCALL brlapi_acceptKeyRanges	(	const brlapi_range_t	ranges[],
		unsigned int	count
	)

Accept some key presses from the braille keyboard

This function asks the server to return the provided key ranges (inclusive) to the application, and not give them to brltty.

The sets of such keys are reset on brlapi_enterTtyMode call.

Parameters

ranges	key ranges, which are inclusive, see Types and Defines forBrlAPI Key Codes about key ranges
count	number of ranges

brlapi_acceptKeys()

int BRLAPI_STDCALL brlapi_acceptKeys	(	brlapi_rangeType_t	type,
		const brlapi_keyCode_t	keys[],
		unsigned int	count
	)

Accept some key presses from the braille keyboard

This function asks the server to give the provided keys to the application, and not give them to brltty.

The sets of such keys are reset on brlapi_enterTtyMode call.

Parameters

type	type of keys to be ignored
keys	array of keys to be ignored
count	number of keys

brlapi_describeKeyCode()

int BRLAPI_STDCALL brlapi_describeKeyCode	(	brlapi_keyCode_t	code,
		brlapi_describedKeyCode_t *	description
	)

Describe the components of a key code.

Parameters

code	the keycode to be described
description	pointer to the structure that receives the description

Returns

0 on success, -1 on error

brlapi_expandKeyCode()

int BRLAPI_STDCALL brlapi_expandKeyCode	(	brlapi_keyCode_t	code,
		brlapi_expandedKeyCode_t *	expansion
	)

Expand the components of a key code

Parameters

code	the key code to be expanded
expansion	pointer to the structure that receives the components

Returns

0 on success, -1 on error

brlapi_ignoreKeyRanges()

int BRLAPI_STDCALL brlapi_ignoreKeyRanges	(	const brlapi_range_t	ranges[],
		unsigned int	count
	)

Ignore some key presses from the braille keyboard

This function asks the server to give the provided key ranges to brltty, rather than returning them to the application via brlapi_readKey().

The sets of such keys are reset on brlapi_enterTtyMode call.

Parameters

ranges	key ranges, which are inclusive, see Types and Defines forBrlAPI Key Codes about key ranges
count	number of ranges

brlapi_ignoreKeys()

int BRLAPI_STDCALL brlapi_ignoreKeys	(	brlapi_rangeType_t	type,
		const brlapi_keyCode_t	keys[],
		unsigned int	count
	)

Ignore some key presses from the braille keyboard

This function asks the server to give the provided keys to brltty, rather than returning them to the application via brlapi_readKey().

The sets of such keys are reset on brlapi_enterTtyMode call.

Parameters

type	type of keys to be ignored
keys	array of keys to be ignored
count	number of keys

brlapi_readKey()

int BRLAPI_STDCALL brlapi_readKey	(	int	wait,
		brlapi_keyCode_t *	code
	)

Read a key from the braille keyboard

This function returns one key press's code.

If NULL or "" was given to brlapi_enterTtyMode(), a brltty command is returned, as described in the documentation for brlapi_keyCode_t . It is hence pretty driver-independent, and should be used by default when no other option is possible.

By default, all commands but those which restart drivers and switch virtual terminals are returned to the application and not to brltty. If the application doesn't want to see some command events, it should call brlapi_ignoreKeys()

If a driver name was given to brlapi_enterTtyMode(), a driver-specific keycode is returned, as specified by the braille driver, usually in <brltty/brldefs-xy> where xy is the driver's code. It generally corresponds to the very code that the terminal tells to the driver. This should only be used by applications which are dedicated to a particular braille terminal. Hence, checking the terminal type thanks to a call to brlapi_getDriverName() before getting tty control is a pretty good idea.

By default, all the keypresses will be passed to the client, none will go through brltty, so the application will have to handle console switching itself for instance.

Parameters

wait	tells whether the call should block until a key is pressed (1) or should only probe key presses (0);
code	holds the key code if a key press is indeed read.

Returns

-1 on error or signal interrupt and *code is then undefined, 0 if block was 0 and no key was pressed so far, or 1 and *code holds the key code.

Programming hints:

If your application is only driven by braille command keypresses, you can just call brlapi_readKey(1, &code) so that it keeps blocking, waiting for keypresses.

Else, you'll probably want to use the file descriptor returned by brlapi_openConnection() or brlapi_getFileDescriptor() in your "big polling loop". For instance:

• in a select() loop, just add it to the readfds and exceptfds file descriptor sets;
• in a gtk or atspi application, use g_io_add_watch(fileDescriptor, G_IO_IN|G_IO_ERR|G_IO_HUP, f, data) for adding a callback called f;
• in an Xt/Xaw/motif-based application, use XtAppAddInput(app_context, fileDescriptor, XtInputReadMask|XtInputExceptMask, f, data)
• etc.

and then, when you detect inbound trafic on the file descriptor, do something like this:

while (brlapi_readKey(0, &code) { // process keycode code // ... }

The while loop is needed for processing all pending key presses, else some of them may be left in libbrlapi's internal key buffer and you wouldn't get them immediately.

Note

If the read is interrupted by a signal or by a parameter change notification, brlapi_readKey() will return -1, brlapi_errno will be BRLAPI_ERROR_LIBCERR and errno will be EINTR.

brlapi_readKeyWithTimeout()

int BRLAPI_STDCALL brlapi_readKeyWithTimeout	(	int	timeout_ms,
		brlapi_keyCode_t *	code
	)

Read a key from the braille keyboard, unless a timeout expires

This function works like brlapi_readKey, except that parameter wait is replaced by a timeout_ms parameter

Parameters

timeout_ms	specifies how long the function should wait for a keypress.
code	holds the key code if a key press is indeed read.

Returns

-1 on error, signal interrupt or parameter change notification and *code is then undefined, 0 if the timeout expired and no key was pressed, or 1 and *code holds the key code.

If the timeout expires without any key being pressed, 0 is returned.

If timeout_ms is set to 0, this function looks for key events that have been already received, but does not wait at all if no event was received.

If timeout_ms is set to a negative value, this function behaves like brlapi_readKey, i.e. it uses an infinite timeout.