BInputServerMethod
is a base class for input methods; these are instances
of BInputServerMethod
that act as an interface between the user and
languages using character sets that can't be easily represented on
standard keyboards, such as the Japanese input method that comes with
BeOS.
Input methods generally handle B_KEY_DOWN
messages in their
Filter()
function (see
BInputServerFilter),
keeping some sort of state around to translate these standard
keyboard messages into new B_KEY_DOWN messages
representing another character set. An input method can handle any input
event, they're not limited to keyboard events.
Writing an input method is an involved process, even though the
BInputServerMethod
protocol is relatively simple. If you're working on an input
method, please feel free to contact Be Developer Technical Support
(devsupport@be.com) for additional information.
Input methods insert B_INPUT_METHOD_EVENT messages (using their
EnqueueMessage()
function) into the Input Server's event stream. These
messages let BView
subclasses work together with your input method to
create a seamless experience for the user.
Each B_INPUT_METHOD_EVENT message contains a
be:opcode field (an int32
value) indicating the kind of event:
| Constant | Description |
|---|---|
| Indicates that a new input transaction has begun.
Add a |
| Indicates that the transaction is over. |
In between the B_INPUT_METHOD_STARTED and B_INPUT_METHOD_STOPPED
messages, you'll send B_INPUT_METHOD_CHANGED and
B_INPUT_METHOD_LOCATION_REQUEST messages as the transaction proceeds.
B_INPUT_METHOD_CHANGED does most of the work in
an input transaction; add the following important fields:
| Entry | Type | Description |
|---|---|---|
be:string | B_STRING_TYPE | The text the user is currently entering; the
receiver will display it at the current insertion point.
BTextView
also highlights the text in blue to show that it's part of a transitory
transaction. |
be:selection | B_INT32_TYPE | A pair of B_INT32_TYPE offsets into the
be:string if part of be:string is
current selected. BTextView
highlights this selection in red instead of drawing it in blue. |
be:clause_start | B_INT32_TYPE | Zero or more offsets into the be:string for
handling languages (such as Japanese) that separate a sentence or phrase
into numerous clauses. An equal number of be:clause_start and
be:clause_end pairs delimit these clauses;
BTextView separates the
blue/red highlighting wherever there is a clause boundary. |
be:clause_end | B_INT32_TYPE | Zero or more offsets into be:string; there
must be as many be:clause_end entries
as there are be:clause_start. |
be:confirmed | B_BOOL_TYPE | True when the user has entered and "confirmed"
the current string and wishes to end the transaction.
BTextView
unhighlights the blue/red text and waits for a B_INPUT_METHOD_STOPPED (to
close the transaction) or another B_INPUT_METHOD_CHANGED (to start a new
transaction immediately). |
B_INPUT_METHOD_LOCATION_REQUEST is the input method's way of asking for
the on-screen location of each character in be:string. This information
can be used by the input method to pop up additional windows giving the
user an opportunity to select characters from a list or anything else
that makes sense. When you send a B_INPUT_METHOD_LOCATION_REQUEST, the
receiver will reply to the be:reply_to messenger (that you sent in your
B_INPUT_METHOD_STARTED message) with a B_INPUT_METHOD_EVENT message,
filling in the following fields:
| Entry | Type | Description |
|---|---|---|
be:opcode | B_INT32_TYPE | Set to B_INPUT_METHOD_LOCATION_REQUEST. |
be:location_reply | B_POINT_TYPE | The co-ordinates of each character (there
should be one be:location_reply for every
character in be:string)
relative to the display (not your view or your window). |
be:height_reply | B_FLOAT_TYPE | The height of each character in be:string. |
To create a new input method, you must:
Create a subclass of
BInputServerMethod
Implement the instantiate_input_method() C function to create an
instance of your
BInputServerMethod
subclass
Compile the class and function as an add-on
Install the add-on in one of the input method directories
At boot time (or whenever the Input Server is restarted; see "Dynamic
Loading"), the Input Server loads the add-ons it finds in the input
method directories. For each add-on it finds, the Server invokes
instantiate_input_method() to get a pointer to the add-on's
BInputServerMethod object. After constructing the object, the Server
calls InitCheck() to give the add-on a chance to bail out if the
constructor failed.
The input server looks for input methods in the "input_server/methods"
subdirectories of B_BEOS_ADDONS_DIRECTORY,
B_COMMON_ADDONS_DIRECTORY, and
B_USER_ADDONS_DIRECTORY.
You can install your input devices in the latter two
directories—i.e. those under B_COMMON_ADDONS_DIRECTORY, and
B_USER_ADDONS_DIRECTORY.
The B_BEOS_ADDONS_DIRECTORY is reserved for add-ons that are supplied
by the BeOS.
