BrlAPI: Reading key presses

BrlAPI 0.8

Data Structures | Macros | Enumerations | Functions
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.