path: root/xorg-server/xkb/XKM_file_format.txt

                        XKM File Format Description
                                Version 15

1. Introduction

The XKM file format is the exchange format for XKB keyboard descriptions
between the server and xkbcomp. Usually, the server forks off xkbcomp,
xkbcomp compiles the XKM format from the given parameters.
The resulting XKM file is put into a directory readable by the server and
then parsed.

The XKM format is little more than a binary dump of various XKB-specific
structures and hence tied to the ABI of the server.

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1.1 About this file format description

This description was produced by analyzing the XKM parsing code. Parts of
the file description present in the original format specification may be
missing. This description thus cannot be a reference document for XKM
implementations.

No description of the meaning of the various fields is given here. Refer to
the XKB protocol specification for more details.
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2. Notations used in this document

Notation for structures:

┌───
  Name of struct
	name of field:		type or fixed value of field
	name of field:		type or fixed value of field
└───

Data types are identical to those used in the X Protocol specification
except where noted otherwise. Structs specific to XKM are prefixed with XKM,
defines specific to the XKB protocol specification are prefixed with Xkb and
their value is equivalent to that in the protocol specification.

Multiple instances of a given type are denoted in the following form:
	name of field:		LISTofFIELDTYPE

Length specifiers for such fields are usually prefixed with num_. For
example, a struct containing a num_foo of 8 and a 'foo' field contains 8
structures of type 'foo'.

Variable length padding is specified as pad(x), where x is the length of the
data to be padded out to a multiple of 4 bytes. For example, given an x of
10, pad(x) would be the remaining 2 bytes to pad the whole struct to 12
bytes.

A special notation is a variable content struct. In this case, the contents
of the struct depend on the value of one or more specific fields.
┌───
  Name of struct
	field:			type or fixed value of field
	field:			type or fixed value of field
	───
	field ⇒ value 1
	⇒
		specific field:		type
		specific field:		type
	───
        field ⇒ value 2
	⇒
		specific field:		type
		specific field:		type
└───
This notation denotes that if field is of value 1, this struct contains the
specific fields listed underneath value 1.

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3. XKM Format

The XKM format is a binary format with structs usually being padded to a
multiple of 4 bytes. No provisions for endianess are provided, the parser is
left to guess the endianess of the XKM file.

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3.1 Common data types

┌───
  XKMCountedString
	count:			CARD16
	string:			count * CHAR
	pad:			pad(count + 2)
└───

XKMCountedString is used for user-readable identifiers. Prime example are
the level names and the section names ("complete", "evdev(inet)", etc.)

┌───
  XKMGroupBits:		CARD8
	group1			0x1
	group2			0x2
	group3			0x4
	group4			0x8
└───

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3.2 Header and Table of Contents

┌───
  XKMHeader
	version:		CARD8
	identifier1:		'm'
	identifier2:		'k'
	idenfifier3:		'x'
└───

The XKM file format has a 4 byte header identifying the file and the XKM
version. The header is followed by the table of contents indicating the
sections present in this file.

┌───
  XKMFileInfo
	type:			CARD8
	min_keycode:		CARD8
	max_keycode:		CARD8
	num_sectioninfo:	CARD8
	present:		CARD16
	pad:			CARD16
	sectioninfo:		LISTofXKMSectionInfo
└───

min_keycode and max_keycode specify the keycode range for this keyboard
descriptions. The core protocol requires min_keycode always be equal to or
greater than 8.

┌───
  XKMSectionInfo
	type:			CARD16
		XkmTypesIndex		0
		XkmCompatMapIndex	1
		XkmSymbolsIndex		2
		XkmIndicatorsIndex	3
		XkmKeyNamesIndex	4
		XkmGeometryIndex	5
		XkmVirtualModsIndex	6
	format:			CARD16
	size:			CARD16
	offset:			CARD16
└───

Describes the section found in a chunk of a file. This struct is found
_twice_ in the file per section, once as part of the XKMFileInfo, once at
the beginning of the actual section (see offset).
The type specifies the type of the section, the section is to be parsed
according to this type.
Size and offset specify the size in bytes and the offset into the file in
bytes, respectively.

3.3 Sections

Each section resides at the offset specified in the XKMFileInfo sectioninfo.

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3.3.1 XKMTypes

An XKMTypes section describes the key types defined in a layout. Roughly
speaking, a key type defines how many levels a given key has and which
modifiers change to a particular level.

┌───
  XKMTypesSection
	section_info:		XKMSectionInfo
	name:			XKMCountedString
	num_types:		CARD16
	pad:			CARD16
	types:			LISTofXKMKeyType
└───

┌───
  XKMKeyType
	real_mods:		CARD8
	num_levels:		CARD8
	virt_mods:		CARD16
	num_map_entries: 	CARD8
	num_level_names: 	CARD8
	perserve:	 	CARD8
	pad:			CARD8
	map_entries:		LISTofXKMKTMapEntry
	name:			XKMCountedString
	mods:			LISTofXKMModsDesc
	level_names:		LISXTofXKMCountedString
└───

The num_map_entries specifies the number of structs in both map_entries and mods. mods is only present if preserve is TRUE.

┌───
  XKMKTMapEntry
	level:			CARD8
	real_mods:		CARD8
	virt_mods:		CARD16
└───

┌───
  XKMModsDesc
	real_mods:		CARD8
	pad:			CARD8
	virt_mods:		CARD16
└───

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3.3.2 XKMCompatMap

An XKMCompatMap section describes the actions a keyboard may trigger. This
ranges from the TerminateServer action to simple modifier bits.

┌───
  XKMCompatMap
	section_info:		XKMSectionInfo
	name:			XKMCountedString
	num_si:			CARD16
	group_mask:		XKMGroupBits
	pad:			CARD8
	si:			LISTofXKMSymInterpreterDesc
	groups:			LISTofXKMModsDesc
└───

One XKMModsDesc is present for each bit set in group_mask.

┌───
  XKMSymInterpretDesc
	sym:			CARD32
	mods:			CARD8
	match:			CARD8
	virtual_mod:		CARD8
	flags:			CARD8
	action_type:		CARD8
	action_data:		XKMActionData
└───

Where the action is 7 bytes of CARD8 whose content is determined by
action_type.

┌───
  XKMActionData:
	pad0:			CARD8
	pad1:			CARD16
	pad2:			CARD32
	───
        action_type ⇒ XkbSA_SetMods ||
        action_type ⇒ XkbSA_LatchMods ||
        action_type ⇒ XkbSA_LockMods
	⇒
		flags:			CARD8
		mask:			CARD8
		real_mods:		CARD8
		vmods1:			CARD8
		vmods2:			CARD8
		pad:			CARD16
	───
        action_type ⇒ XkbSA_SetGroup ||
        action_type ⇒ XkbSA_LatchGroup ||
        action_type ⇒ XkbSA_LockGroup
	⇒
		flags:			CARD8
		group_XXX:		CARD8
		pad0:			CARD8
		pad1:			CARD32
	───
        action_type ⇒ XkbSA_MovePtr
	⇒
		flags:			CARD8
		high_XXX:		CARD8
		low_XXX:		CARD8
		high_YYY:		CARD8
		low_YYY:		CARD8
		pad:			CARD16
	───
        action_type ⇒ XkbSA_PtrBtn ||
        action_type ⇒ XkbSA_LockPtrBtn
	⇒
		flags:			CARD8
		count:			CARD8
		button:			CARD8
		pad:			CARD32
	───
        action_type ⇒ XkbSA_DeviceBtn ||
        action_type ⇒ XkbSA_LockLockPtrBtn
	⇒
		flags:			CARD8
		count:			CARD8
		button:			CARD8
		device:			CARD8
		pad0:			CARD8
		pad1:			CARD16
	───
        action_type ⇒ XkbSA_SetPtrDflt
	⇒
		flags:			CARD8
		affect:			CARD8
		valueXXX:		CARD8
		pad0:			CARD32
	───
        action_type ⇒ XkbSA_ISOLock
	⇒
		flags:			CARD8
		mask:			CARD8
		real_mods:		CARD8
		group_XXX:		CARD8
		affect:			CARD8
		vmods1:			CARD8
		vmods1:			CARD8
	───
        action_type ⇒ XkbSA_SwitchScreen
	⇒
		flags:			CARD8
		screenXXX:		CARD8
		pad0:			CARD8
		pad1:			CARD32
	───
        action_type ⇒ XkbSA_SetControls ||
        action_type ⇒ XkbSA_LockControls
	⇒
		flags:			CARD8
		ctrls3:			CARD8
		ctrls2:			CARD8
		ctrls1:			CARD8
		ctrls0:			CARD8
		pad:			CARD16
	───
        action_type ⇒ XkbSA_RedirectKey
	⇒
		new_key:		CARD8
		mods_mask:		CARD8
		mods:			CARD8
		vmods_mask0:		CARD8
		vmods_mask1:		CARD8
		vmods0:			CARD8
		vmods1:			CARD8
	───
        action_type ⇒ XkbSA_DeviceValuator
	⇒
		device:		CARD8
		v1_what:		CARD8
		v1_idx:			CARD8
		v1_value:		CARD8
		v2_what:		CARD8
		v2_idx:			CARD8
		v2_value:		CARD8
		pad:			CARD8
	───
        action_type ⇒ XkbSA_XFree86Private ||
        action_type ⇒ XkbSA_Terminate
	⇒
		pad0:			CARD8
		pad1:			CARD16
		pad2:			CARD32
	───
        action_type ⇒ XkbSA_ActionMessage
	⇒
		press_msg:		BOOL
		release_msg:		BOOL
		gen_event:		BOOL
		message:		4 * CHAR
└───

Note: XkbSA_ActionMessage is currently unsupported and the contents are
ignored.

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3.3.3 XkmSymbols

The symbols in a keymap define the actual keysyms each key may produce.

┌───
  XKMSymbols
	section_info:		XKMSectionInfo
	name:			XKMCountedString
	min_keycode:		CARD8
	max_keycode:		CARD8
	group_names_mask:	XKMGroupBits
	num_vmod_maps:		CARD8
	group_names:		LISTofXKMCountedString
	keysyms:		XKMKeysymMapDesc
	vmod_maps:		XKMVModMapDesc
└───
One group_name is present for each bit set in group_names_mask.
The number of keysyms present is max_keycode - min_keycode + 1.

┌───
  XKMKeysymMapDesc
	width:			CARD8
	num_groups:		CARD8
	modifier_map:		CARD8
	flags:			CARD8
	names:			LISTofXKMCountedString
	syms:			LISTofCARD32
	behavior:		XKMBehaviorDesc
└───

Presence of names is conditional on the XkmKeyHasTypes flag. The number of
strings is equal to the number of group bits in group_names_mask in the
preceeding XKMSymbols section.
The number of elements in syms is equal to width * num_groups.
Presence of behavior is conditional on the XkmKeyHasBehavior flag.

┌───
  XKMKeyBehaviorDesc
	type:			CARD8
	data:			CARD8
	pad:			CARD16
└───

┌───
  XKMVModMapDesc
	key:			CARD8
	pad:			CARD8
	vmods:			CARD16
└───

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3.3.4 XKMIndicators

┌───
  XKMIndicators
	section_info:		XKMSectionInfo
	name:			XKMCountedString
	num_indicators:		CARD8
	pad0:			CARD8
	pad1:			CARD16
	indicators:		LISTofXKMIndicatorMapDesc
└───

┌───
  XKMIndicatorMapDesc
	name:			XKMCountedString
	indicator:		CARD8
	flags:			CARD8
	which_mods:		CARD8
	real_mods:		CARD8
	vmods:			CARD16
	which_groups:		CARD8
	groups:			CARD8
	ctrls:			CARD32
└───
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3.3.5 XKMKeyNames

┌───
  XKMKeyNames
	section_info:		XKMSectionInfo
	name:			XKMCountedString
	min_keycode:		CARD8
	max_keycode:		CARD8
	num_aliases:		CARD8
	pad:			CARD8
	keynames:		LISTofXKMKeyname
	aliases:		LISTofXKMKeyAlias
└───

keynames contains max_keycode - min_keycode + 1 entries.

┌───
  XkmKeyname
	name:			4 * CHAR8
└───

┌───
  XkmKeyAlias
	real:			XkmKeyname
	alias:			XkmKeyname
└───

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3.3.5 XKMGeometry

┌───
  XKMGeometry
	section_info:		XKMSectionInfo
	name:			XKMCountedString
	width_mm:		CARD16
	height_mm:		CARD16
	base_color_ndx:		CARD8
	label_color_ndx:	CARD8
	num_properties:		CARD16
	num_colors:		CARD16
	num_shapes:		CARD16
	num_sections:		CARD16
	num_doodads:		CARD16
	num_key_aliases:	CARD16
	pad:			CARD16
	label_font:		XKMCountedString
	properties:		LISTofXKMGeomProperty
	colors:			LISTofXKMCountedString
	shapes:			LISTofXKMGeomShape
	sections:		LISTofXKMGeomSection
	doodads:		LISTofXKMGeomDoodad
	key_aliases:		LISTofXKMKeyAlias
└───

┌───
  XKMGeomProperty
	name:			XKMCountedString
	value:			XKMCountedString

└───

┌───
  XKMGeomShape
	name:			XKMCountedString
	num_outlines:		CARD8
	primary_idx:		CARD8
	approx_idx:		CARD8
	pad:			CARD8
	outlines:		LISTofXKMOutlineDesc
└───

┌───
  XKMOutlineDesc
	num_points:		CARD8
	corner_radius:		CARD8
	pad:			CARD16
	points:			LISTofXKMPointDesc
└───

┌───
  XKMPointDesc
	x:			INT16
	y:			INT16
└───

┌───
  XKMGeomSection
	name:			XKMCountedString
	top:			INT16
	left:			INT16
	width:			CARD16
	height:			CARD16
	angle:			INT16
	priority:		CARD8
	num_rows:		CARD8
	num_doodads:		CARD8
	num_overlays:		CARD8
	pad:			CARD16
	rows:			LISTofXKMRowDesc
	doodads:		LISTofXKMGeomDoodad
	overlays:		LISTofXKMGeomOverlay
└───

┌───
  XKMRowDesc
	top:			INT16
	left:			INT16
	num_keys:		CARD8
	vertical:		BOOL
	pad:			CARD16
	keys:			XKMKeyDesc
└───

┌───
  XKMKeyDesc
	name:			XKMKeyname
	gap:			INT16
	shape_idx:		CARD8
	color_idx:		CARD8
└───

┌───
  XKMGeomDoodad
	name:			XKMCountedString
	type:			CARD8
	priority:		CARD8
	top:			INT16
	left:			INT16
	pad1:			CARD16
	pad2:			CARD32
	pad3:			CARD32
	───
        type ⇒ XkbOutlineDoodad ||
        type ⇒ XkbSolideDoodad
	⇒
		type:			CARD8
		priority:		CARD8
		top:			INT16
		left:			INT16
		angle:			INT16
		color_idx:		CARD8
		shape_idx:		CARD8
		pad0:			CARD16
		pad1:			CARD32
	───
        type ⇒ XkbTextDoodad
	⇒
		type:			CARD8
		priority:		CARD8
		top:			INT16
		left:			INT16
		angle:			INT16
		width:			CARD16
		height:			CARD16
		color_idx:		CARD8
		pad0:			CARD8
		pad1:			CARD16
		text:			XKMCountedString
		font:			XKMCountedString
	───
        type ⇒ XkbIndicatorDoodad
	⇒
		type:			CARD8
		priority:		CARD8
		top:			INT16
		left:			INT16
		shape_idx:		CARD8
		on_color_idx:		CARD8
		off_color_idx:		CARD8
		pad0:			CARD8
		pad1:			CARD16
		pad2:			CARD32
	───
        type ⇒ XkbLogoDoodad
	⇒
		type:			CARD8
		priority:		CARD8
		top:			INT16
		left:			INT16
		angle:			INT16
		color_idx:		CARD8
		shape_idx:		CARD8
		pad0:			CARD16
		pad1:			CARD32
		logo_name:		XKMCountedString
└───

WARNING: XKMGeomDoodad has variable length depending on the type.
NOTE: The current server implementation does not use all fields of all
structures.

┌───
  XKMOverlayDesc
	name:			XKMCountedString
	num_rows:		CARD8
	pad0:			CARD8
	pad1:			CARD16
	rows:			LISTofXKMOverlayRowDesc
└───

┌───
  XKMOverlayRowDesc
	name:			XKMCountedString
	row_under:		CARD8
	num_keys:		CARD8
	pad:			CARD16
	keys:			LISTofXKMOverlayKeyDesc
└───

┌───
  XKMOverlayKeyDesc
	over:			XKMKeyname
	under:			XKMKeyname
└───

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3.3.6 XKMVirtualMods

┌───
  XKMOverlayRowDesc
	section_info:		XKMSectionInfo
	name:			XKMCountedString
	bound_mask:		SETofVMODBITS
	named_mask:		SETofVMODBITS
	vmods:			LISTofCARD8
	pad:			pad(vmods)
	names:			LISTofXKMCountedString
└───

	VMODBITS:		CARD16

Number of elements in vmods is equal to the number of bits set in
bound_mask. The padding completes vmods to a multiple of 4 byte units.
Number of elements in names is equal to the number of bits set in
named_mask.