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Namespace

All calls, types and enums are prefixed with the namespace prefix km_kbp_

Idioms

Error handling

Follows a COM HRESULT style model where functions that can fail will always return a status value and all other results are returned via outparams passed to the function. Only attribute accessor functions which cannot fail, may return their results via return results.

Passing variable length data out

Almost all calls marshalling variable length aggregate data in or out of an API object take the form:

km_kbp_status fn_name(object_ref, buffer_ptr, size_ptr)

where the buffer_ptr is nullable and all other arguments are required (will result in an KM_KBP_STATUS_INVALID_ARGUMENT status being returned if nulled). When buffer_ptr is nullptr or 0 the function will place the size of the required buffer in the variable pointed to by size_ptr.

Resource management

Calls which result in the allocation of resources, regardless of resulting ownership, are of the form:

km_kbp_status fn_name(object_ref, handle_out_ptr)

where handle_out_ptr is a valid pointer to a caller allocated variable to hold the resulting resource handle. This is often a reference to a created object. Unless stated all arguments are required (will result in an KM_KBP_STATUS_INVALID_ARGUMENT status being returned if nulled).

All dispose calls are designed to accept nullptr or 0 as a valid value and will do nothing in that event.

Fixed size attribute access

For accessors to fixed size attributes of an object these will take the form:

attr_value fn_name(object_ref)

object_ref is required to be valid and will result in a nonsense value being returned if nullptr or 0.

Versioning scheme

This follows the libtool interface versioning scheme of current.age.revision:

current

The most recent interface number that the engine implements.

age

How many interface numbers back from current the library implements. E.g. 5.2.0 would mean the library provides interface versions 3-5 and 5.0.0 would mean just interface version 5 and nothing older.

revision

The implementation version of the current interface. This represents improvements to the code that don't change the intended behaviour of the interface such as bug fixes and optimisations.

For Linux and other OS which support this scheme the dynamic linker will automatically choose the most updated version if more than one implementation is available. For Windows or dynamic loaded shared objects on Linux you can use the km_kbp_get_engine_attrs call and Library version macros to check the loaded DLL supplies the correct interface.

Common functions, types, and macros

Basic types

Fundamental types for representing data passed across the API.

Type	C/C++ type	Purpose
km_kbp_cp	uint16_t/char16_t	Represents a UTF16 codepoint, most strings are passed as UTF16.
km_kbp_usv	uint32_t/char32_t	An integral type capable of holding a single Unicode Scalar Value, a decoded UTF codepoint.
km_kbp_virtual_key	uint16_t	An integral type capable of holding a platform specific virtual key code.
km_kbp_status	uint32_t	An integral 32 bit wide type capable of holding any valid status code as defined by the enum km_kbp_status_codes.
km_kbp_modifier_state	uint16_t	An integral type bitmask representing the state of each modifier key.

Resource types

Opaque types for representing resources provided or created by the keyboard processor implementation.

Type	Purpose
km_kbp_keyboard	Represents a keyboard loaded from disk, that can be executed by the keyboard processor to consume events, update state associated with an insertion point and produce action items. A keyboard object may be referenced by any number of state objects but must be disposed of after all state objects referencing it have first been disposed of.
km_kbp_state	Represents all state associated with an insertion point using a keyboard. This tracks context, and current action items resulting from a processed keyboard event. There can be many state objects using the same keyboard. A state object may not live longer than the keyboard it manages state for.
km_kbp_context	Represents the pre-context of an insertion point and may be set, queried, append or shrunk by one or more context items. A context object is a sub-part of the state object, and a context handle may not be used after its state object has been disposed of.

Library version macros

Description

These macros evaluate to the version of the library your binary was compiled against, which may not be the same as the version returned by km_kbp_get_engine_attrs. See Versioning scheme.

Specification

    #define KM_KBP_LIB_CURRENT  @lib_curr@
    #define KM_KBP_LIB_AGE      @lib_age@
    #define KM_KBP_LIB_REVISION @lib_rev@

km_kbp_status_codes enum

Description

An error code mechanism similar to COM’s HRESULT scheme (unlike COM, any non-zero value is an error).

Specification

    enum km_kbp_status_codes {
      KM_KBP_STATUS_OK = 0,
      KM_KBP_STATUS_NO_MEM = 1,
      KM_KBP_STATUS_IO_ERROR = 2,
      KM_KBP_STATUS_INVALID_ARGUMENT = 3,
      KM_KBP_STATUS_KEY_ERROR = 4,
      KM_KBP_STATUS_INSUFFICENT_BUFFER = 5,
      KM_KBP_STATUS_INVALID_UTF = 6,
      KM_KBP_STATUS_INVALID_KEYBOARD = 7,
      KM_KBP_STATUS_OS_ERROR = 0x80000000
    };

Values

KM_KBP_STATUS_OK

Success code. Call completed as documented.

KM_KBP_STATUS_NO_MEM

The call failed to allocate memory during its execution, causing it to fail.

KM_KBP_STATUS_IO_ERROR

The call performed an I/O operation which failed, causing it to fail.

KM_KBP_STATUS_INVALID_ARGUMENT

The call detected one of its parameters was invalid or unsafe.

KM_KBP_STATUS_KEY_ERROR

The provided key or index into a collection object was not present.

KM_KBP_STATUS_INSUFFICENT_BUFFER

The provided buffer did not contain enough space to fully encode or copy the result of this call.

KM_KBP_STATUS_INVALID_UTF

A malformed or partial UTF sequence prevented complete decoding of a unicode string.

KM_KBP_STATUS_INVALID_KEYBOARD

An attempt to decode a keyboard file failed.

KM_KBP_STATUS_OS_ERROR

This allows encapsulating a platform error code: the remaining 31 low bits are the error code returned by the OS for cases where the failure mode is platform specific. For HRESULT codes this only permits failure codes to be passed and not success codes.

km_kbp_attr struct

Description

A structure describing information about the keyboard processor, implementing this API.

Specification

    typedef struct {
      size_t      max_context;
      uint16_t    current;
      uint16_t    revision;
      uint16_t    age;
      uint16_t    technology;
      char const *vendor;
    } km_kbp_attr;

Members

max_context

Maximum context size supported by processor.

current

Current API number supported.

revision

Implementation number of current API.

age

current - age == Oldest API number supported.

technology

A bit field of km_kbp_tech_value values, specifiying which Keyboard technologies the engine supports.

vendor

A UTF-8 encoded string identifying the implementer of the processor.

km_kbp_tech_value enum

Description

Values for a bit field indicating which keyboarding technologies a keyboard processor supports.

Specification

    enum km_kbp_tech_value {
      KM_KBP_TECH_UNSPECIFIED = 0,
      KM_KBP_TECH_MOCK        = 1 << 0,
      KM_KBP_TECH_KMX         = 1 << 1,
      KM_KBP_TECH_LDML        = 1 << 2
    };

Values

KM_KBP_TECH_UNSPECIFIED

The keyboard processor implementation does not disclose which technologies it implements.

KM_KBP_TECH_MOCK

The keyboard processor implements a simple en-US keyboard for the purposes of testing the API.

KM_KBP_TECH_UNSPECIFIED

The keyboard processor implements a Keyman KMX compatible engine.

KM_KBP_TECH_UNSPECIFIED

The keyboard processor implements a LDML capable processing engine.

km_kbp_get_engine_attrs()

Description

Get access processors attributes describing version and technology implemented.

Specification

    KMN_API
    km_kbp_attr const *
    km_kbp_get_engine_attrs(km_kbp_state const *state);

Parameters

state

An opaque pointer to an km_kbp_state.

Returns

A pointer to a km_kbp_attr structure. Do not modify the contents of this structure.