Block diagram
Portable Compiled Format (PCF) font is a bitmap font format originating from X11 Window System. It matches BDF format (which is text-based) closely, but instead being binary and platform-independent (as opposed to previously used SNF binary format) due to introduced features to handle different endianness and bit order.
The overall composition of the format is straightforward: it's more or less classic directory of type-offset-size pointers, pointing to what PCF format calls "tables". Each table carries a certain piece of information related to the font (metadata properties, metrics, bitmaps, mapping of glyphs to characters, etc).
This page hosts a formal specification of Portable Compiled Format (PCF) font using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
meta:
id: pcf_font
title: Portable Compiled Format (PCF) font
file-extension: pcf
xref:
justsolve: PCF
wikidata: Q3398726
license: CC0-1.0
ks-version: 0.9
imports:
- /common/bytes_with_io
encoding: UTF-8
endian: le
doc: |
Portable Compiled Format (PCF) font is a bitmap font format
originating from X11 Window System. It matches BDF format (which is
text-based) closely, but instead being binary and
platform-independent (as opposed to previously used SNF binary
format) due to introduced features to handle different endianness
and bit order.
The overall composition of the format is straightforward: it's more
or less classic directory of type-offset-size pointers, pointing to
what PCF format calls "tables". Each table carries a certain
piece of information related to the font (metadata properties,
metrics, bitmaps, mapping of glyphs to characters, etc).
doc-ref: https://fontforge.org/docs/techref/pcf-format.html
seq:
- id: magic
-orig-id: header
contents: [0x1, "fcp"]
- id: num_tables
-orig-id: table_count
type: u4
- id: tables
type: table
repeat: expr
repeat-expr: num_tables
types:
table:
doc: |
Table offers a offset + length pointer to a particular
table. "Type" of table references certain enum. Applications can
ignore enum values which they don't support.
-webide-representation: "{type}"
seq:
- id: type
type: u4
enum: types
- id: format
type: format
- id: len_body
-orig-id: size
type: u4
- id: ofs_body
-orig-id: offset
type: u4
instances:
body:
pos: ofs_body
size: len_body
type:
switch-on: type
cases:
'types::properties': properties
# TODO: accelerators
# TODO: metrics
# TODO: ink_metrics
'types::bitmaps': bitmaps
'types::bdf_encodings': bdf_encodings
'types::swidths': swidths
'types::glyph_names': glyph_names
# TODO: bdf_accelerators
types:
properties:
doc: |
Array of properties (key-value pairs), used to convey different X11
settings of a font. Key is always an X font atom.
doc-ref: 'https://fontforge.org/docs/techref/pcf-format.html#properties-table'
-webide-representation: "{num_props:dec} properties"
seq:
- id: format
type: format
- id: num_props
type: u4
- id: props
type: prop
repeat: expr
repeat-expr: num_props
- id: padding
size: '(num_props & 3) == 0 ? 0 : (4 - (num_props & 3))'
# In reality: align to next 4-byte boundary
- id: len_strings
type: u4
- id: strings
size: len_strings
type: bytes_with_io
doc: |
Strings buffer. Never used directly, but instead is
addressed by offsets from the properties.
types:
prop:
doc: |
Property is a key-value pair, "key" being always a
string and "value" being either a string or a 32-bit
integer based on an additinal flag (`is_string`).
Simple offset-based mechanism is employed to keep this
type's sequence fixed-sized and thus have simple access
to property key/value by index.
-webide-representation: "{name} => {str_value}/{int_value}"
seq:
- id: ofs_name
type: u4
doc: Offset to name in the strings buffer.
- id: is_string
-orig-id: isStringProp
type: u1
doc: |
Designates if value is an integer (zero) or a string (non-zero).
- id: value_or_ofs_value
type: u4
doc: |
If the value is an integer (`is_string` is false),
then it's stored here. If the value is a string
(`is_string` is true), then it stores offset to the
value in the strings buffer.
instances:
name:
io: _parent.strings._io
pos: ofs_name
type: strz
doc: |
Name of the property addressed in the strings buffer.
-webide-parse-mode: eager
str_value:
io: _parent.strings._io
pos: value_or_ofs_value
type: strz
if: is_string != 0
doc: |
Value of the property addressed in the strings
buffer, if this is a string value.
-webide-parse-mode: eager
int_value:
value: value_or_ofs_value
if: is_string == 0
doc: |
Value of the property, if this is an integer value.
-webide-parse-mode: eager
# As of Kaitai Struct 0.9, `value` fails with:
#
# "can't combine output types: StrFromBytesType(BytesTerminatedType(0,false,true,true,None),UTF-8) vs IntMultiType(false,Width4,Some(LittleEndian))"
#
# ... so currently it's commented out.
#value:
# value: '(is_string != 0) ? str_value : int_value'
bitmaps:
doc: |
Table containing uncompressed glyph bitmaps.
doc-ref: 'https://fontforge.org/docs/techref/pcf-format.html#the-bitmap-table'
seq:
- id: format
type: format
- id: num_glyphs
-orig-id: glyph_count
type: u4
- id: offsets
type: u4
repeat: expr
repeat-expr: num_glyphs
- id: bitmap_sizes
type: u4
repeat: expr
repeat-expr: 4
bdf_encodings:
doc: |
Table that allows mapping of character codes to glyphs present in the
font. Supports 1-byte and 2-byte character codes.
Note that this mapping is agnostic to character encoding itself - it
can represent ASCII, Unicode (ISO/IEC 10646), various single-byte
national encodings, etc. If application cares about it, normally
encoding will be specified in `properties` table, in the properties named
`CHARSET_REGISTRY` / `CHARSET_ENCODING`.
doc-ref: 'https://fontforge.org/docs/techref/pcf-format.html#the-encoding-table'
seq:
- id: format
type: format
- id: min_char_or_byte2
type: u2
- id: max_char_or_byte2
type: u2
- id: min_byte1
type: u2
- id: max_byte1
type: u2
- id: default_char
type: u2
- id: glyph_indexes
-orig-id: glyphindeces
type: u2
repeat: expr
repeat-expr: (max_char_or_byte2 - min_char_or_byte2 + 1) * (max_byte1 - min_byte1 + 1)
swidths:
doc: |
Table containing scalable widths of characters.
doc-ref: 'https://fontforge.org/docs/techref/pcf-format.html#the-scalable-widths-table'
-webide-representation: '{num_glyphs:dec} glyphs'
seq:
- id: format
type: format
- id: num_glyphs
type: u4
- id: swidths
type: u4
repeat: expr
repeat-expr: num_glyphs
doc: |
The scalable width of a character is the width of the corresponding
PostScript character in em-units (1/1000ths of an em).
glyph_names:
doc: |
Table containing character names for every glyph.
doc-ref: 'https://fontforge.org/docs/techref/pcf-format.html#the-glyph-names-table'
-webide-representation: '{num_glyphs:dec} glyphs'
seq:
- id: format
type: format
- id: num_glyphs
type: u4
- id: names
type: string_ref
repeat: expr
repeat-expr: num_glyphs
doc: |
Glyph names are represented as string references in strings buffer.
- id: len_strings
-orig-id: string_size
type: u4
- id: strings
size: len_strings
type: bytes_with_io
doc: |
Strings buffer which contains all glyph names.
types:
string_ref:
-webide-representation: '{value}'
seq:
- id: ofs_string
type: u4
instances:
value:
io: _parent.strings._io
pos: ofs_string
type: strz
-webide-parse-mode: eager
format:
doc: |
Table format specifier, always 4 bytes. Original implementation treats
it as always little-endian and makes liberal use of bitmasking to parse
various parts of it.
TODO: this format specification recognizes endianness and bit
order format bits, but it does not really takes any parsing
decisions based on them.
doc-ref: 'https://fontforge.org/docs/techref/pcf-format.html#file-header'
seq:
- id: padding1
type: b2
- id: scan_unit_mask
type: b2
- id: is_most_significant_bit_first
-orig-id: PCF_BYTE_MASK
type: b1
- id: is_big_endian
-orig-id: PCF_BYTE_MASK
type: b1
doc: If set, then all integers in the table are treated as big-endian
- id: glyph_pad_mask
type: b2
-orig-id: PCF_GLYPH_PAD_MASK
- id: format
type: u1
- id: padding
type: u2
enums:
types:
1:
id: properties
-orig-id: PCF_PROPERTIES
2:
id: accelerators
-orig-id: PCF_ACCELERATORS
4:
id: metrics
-orig-id: PCF_METRICS
8:
id: bitmaps
-orig-id: PCF_BITMAPS
0x10:
id: ink_metrics
-orig-id: PCF_INK_METRICS
0x20:
id: bdf_encodings
-orig-id: PCF_BDF_ENCODINGS
0x40:
id: swidths
-orig-id: PCF_SWIDTHS
0x80:
id: glyph_names
-orig-id: PCF_GLYPH_NAMES
0x100:
id: bdf_accelerators
-orig-id: PCF_BDF_ACCELERATORS