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keyboard stuff
1# QMK Font Format {#qmk-font-format}
2
3QMK uses a font format _("Quantum Font Format" - QFF)_ specifically for resource-constrained systems.
4
5This format is capable of encoding 1-, 2-, 4-, and 8-bit-per-pixel greyscale- and palette-based images into a font. It also includes RLE for pixel data for some basic compression.
6
7All integer values are in little-endian format.
8
9The QFF is defined in terms of _blocks_ -- each _block_ contains a _header_ and an optional _blob_ of data. The _header_ contains the block's _typeid_, and the length of the _blob_ that follows. Each block type is denoted by a different _typeid_ has its own block definition below. All blocks are defined as packed structs, containing zero padding between fields.
10
11The general structure of the file is:
12
13* _Font descriptor block_
14* _ASCII glyph block_ (optional, only if ASCII glyphs are included)
15* _Unicode glyph block_ (optional, only if Unicode glyphs are included)
16* _Font palette block_ (optional, depending on frame format)
17* _Font data block_
18
19## Block Header {#qff-block-header}
20
21The block header is identical to [QGF's block header](quantum_painter_qgf#qgf-block-header), and is present for all blocks, including the font descriptor.
22
23## Font descriptor block {#qff-font-descriptor}
24
25* _typeid_ = 0x00
26* _length_ = 20
27
28This block must be located at the start of the file contents, and can exist a maximum of once in an entire QGF file. It is always followed by either the _ASCII glyph table_ or the _Unicode glyph table_, depending on which glyphs are included in the font.
29
30_Block_ format:
31
32```c
33typedef struct __attribute__((packed)) qff_font_descriptor_v1_t {
34 qgf_block_header_v1_t header; // = { .type_id = 0x00, .neg_type_id = (~0x00), .length = 20 }
35 uint24_t magic; // constant, equal to 0x464651 ("QFF")
36 uint8_t qff_version; // constant, equal to 0x01
37 uint32_t total_file_size; // total size of the entire file, starting at offset zero
38 uint32_t neg_total_file_size; // negated value of total_file_size, used for detecting parsing errors
39 uint8_t line_height; // glyph height in pixels
40 bool has_ascii_table; // whether the font has an ascii table of glyphs (0x20...0x7E)
41 uint16_t num_unicode_glyphs; // the number of glyphs in the unicode table -- no table specified if zero
42 uint8_t format; // frame format, see below.
43 uint8_t flags; // frame flags, see below.
44 uint8_t compression_scheme; // compression scheme, see below.
45 uint8_t transparency_index; // palette index used for transparent pixels (not yet implemented)
46} qff_font_descriptor_v1_t;
47// STATIC_ASSERT(sizeof(qff_font_descriptor_v1_t) == (sizeof(qgf_block_header_v1_t) + 20), "qff_font_descriptor_v1_t must be 25 bytes in v1 of QFF");
48```
49
50The values for `format`, `flags`, `compression_scheme`, and `transparency_index` match [QGF's frame descriptor block](quantum_painter_qgf#qgf-frame-descriptor), with the exception that the `delta` flag is ignored by QFF.
51
52## ASCII glyph table {#qff-ascii-table}
53
54* _typeid_ = 0x01
55* _length_ = 290
56
57If the font contains ascii characters, the _ASCII glyph block_ must be located directly after the _font descriptor block_.
58
59```c
60#define QFF_GLYPH_WIDTH_BITS 6
61#define QFF_GLYPH_WIDTH_MASK ((1<<QFF_GLYPH_WIDTH_BITS)-1)
62#define QFF_GLYPH_OFFSET_BITS 18
63#define QFF_GLYPH_OFFSET_MASK (((1<<QFF_GLYPH_OFFSET_BITS)-1) << QFF_GLYPH_WIDTH_BITS)
64
65typedef struct __attribute__((packed)) qff_ascii_glyph_table_v1_t {
66 qgf_block_header_v1_t header; // = { .type_id = 0x01, .neg_type_id = (~0x01), .length = 285 }
67 uint24_t glyph[95]; // 95 glyphs, 0x20..0x7E, see bits/masks above for values
68} qff_ascii_glyph_table_v1_t;
69// STATIC_ASSERT(sizeof(qff_ascii_glyph_table_v1_t) == (sizeof(qgf_block_header_v1_t) + 285), "qff_ascii_glyph_table_v1_t must be 290 bytes in v1 of QFF");
70```
71
72## Unicode glyph table {#qff-unicode-table}
73
74* _typeid_ = 0x02
75* _length_ = variable
76
77If this font contains unicode characters, the _unicode glyph block_ must be located directly after the _ASCII glyph table block_, or the _font descriptor block_ if the font does not contain ASCII characters.
78
79```c
80typedef struct __attribute__((packed)) qff_unicode_glyph_table_v1_t {
81 qgf_block_header_v1_t header; // = { .type_id = 0x02, .neg_type_id = (~0x02), .length = (N * 6) }
82 struct __attribute__((packed)) { // container for a single unicode glyph
83 uint24_t code_point; // the unicode code point
84 uint24_t glyph; // the glyph information, as per ASCII glyphs above
85 } glyph[N]; // N glyphs worth of data
86} qff_unicode_glyph_table_v1_t;
87```
88
89## Font palette block {#qff-palette-descriptor}
90
91* _typeid_ = 0x03
92* _length_ = variable
93
94The _font palette block_ is identical to [QGF's frame palette block](quantum_painter_qgf#qgf-frame-palette-descriptor), retaining the same _typeid_ of 0x03.
95
96It is only specified in the QFF if the font is palette-based, and follows the _unicode glyph block_ if the font contains any Unicode glyphs, or the _ASCII glyph block_ if the font contains only ASCII glyphs.
97
98## Font data block {#qff-data-descriptor}
99
100* _typeid_ = 0x04
101* _length_ = variable
102
103The _font data block_ is the last block in the file and is identical to [QGF's frame data block](quantum_painter_qgf#qgf-frame-data-descriptor), however has a different _typeid_ of 0x04 in QFF.