ttf_parser/tables/
kerx.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
//! An [Extended Kerning Table](
//! https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6kerx.html) implementation.

// TODO: find a way to test this table
// This table is basically untested because it uses Apple's State Tables
// and I have no idea how to generate them.

use core::num::NonZeroU16;

use crate::kern::KerningPair;
use crate::parser::{FromData, LazyArray32, NumFrom, Offset, Offset32, Stream};
use crate::{aat, GlyphId};

const HEADER_SIZE: usize = 12;

/// A format 0 subtable.
///
/// Ordered List of Kerning Pairs.
///
/// The same as in `kern`, but uses `LazyArray32` instead of `LazyArray16`.
#[derive(Clone, Copy, Debug)]
pub struct Subtable0<'a> {
    /// A list of kerning pairs.
    pub pairs: LazyArray32<'a, KerningPair>,
}

impl<'a> Subtable0<'a> {
    /// Parses a subtable from raw data.
    fn parse(data: &'a [u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        let number_of_pairs = s.read::<u32>()?;
        s.advance(12); // search_range (u32) + entry_selector (u32) + range_shift (u32)
        let pairs = s.read_array32::<KerningPair>(number_of_pairs)?;
        Some(Self { pairs })
    }

    /// Returns kerning for a pair of glyphs.
    #[inline]
    pub fn glyphs_kerning(&self, left: GlyphId, right: GlyphId) -> Option<i16> {
        let needle = u32::from(left.0) << 16 | u32::from(right.0);
        self.pairs
            .binary_search_by(|v| v.pair.cmp(&needle))
            .map(|(_, v)| v.value)
    }
}

/// A state machine entry.
#[derive(Clone, Copy, Debug)]
pub struct EntryData {
    /// An action index.
    pub action_index: u16,
}

impl FromData for EntryData {
    const SIZE: usize = 2;

    #[inline]
    fn parse(data: &[u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        Some(EntryData {
            action_index: s.read::<u16>()?,
        })
    }
}

/// A format 1 subtable.
///
/// State Table for Contextual Kerning.
#[derive(Clone)]
pub struct Subtable1<'a> {
    /// A state table.
    pub state_table: aat::ExtendedStateTable<'a, EntryData>,
    actions_data: &'a [u8],
}

impl<'a> Subtable1<'a> {
    fn parse(number_of_glyphs: NonZeroU16, data: &'a [u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        let state_table = aat::ExtendedStateTable::parse(number_of_glyphs, &mut s)?;

        // Actions offset is right after the state table.
        let actions_offset = s.read::<Offset32>()?;
        // Actions offset is from the start of the state table and not from the start of subtable.
        // And since we don't know the length of the actions data,
        // simply store all the data after the offset.
        let actions_data = data.get(actions_offset.to_usize()..)?;

        Some(Subtable1 {
            state_table,
            actions_data,
        })
    }

    /// Returns kerning at action index.
    #[inline]
    pub fn glyphs_kerning(&self, action_index: u16) -> Option<i16> {
        Stream::read_at(self.actions_data, usize::from(action_index) * i16::SIZE)
    }
}

impl<'a> core::ops::Deref for Subtable1<'a> {
    type Target = aat::ExtendedStateTable<'a, EntryData>;

    fn deref(&self) -> &Self::Target {
        &self.state_table
    }
}

impl core::fmt::Debug for Subtable1<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        write!(f, "Subtable1 {{ ... }}")
    }
}

/// A format 2 subtable.
///
/// Simple n x m Array of Kerning Values.
///
/// The same as in `kern`, but uses 32bit offsets instead of 16bit one.
#[derive(Clone, Copy)]
pub struct Subtable2<'a>(&'a [u8]); // TODO: parse actual structure

impl<'a> Subtable2<'a> {
    /// Returns kerning for a pair of glyphs.
    pub fn glyphs_kerning(&self, left: GlyphId, right: GlyphId) -> Option<i16> {
        let mut s = Stream::new(self.0);
        s.skip::<u32>(); // row_width

        // Offsets are from beginning of the subtable and not from the `data` start,
        // so we have to subtract the header.
        let left_hand_table_offset = s.read::<Offset32>()?.to_usize().checked_sub(HEADER_SIZE)?;
        let right_hand_table_offset = s.read::<Offset32>()?.to_usize().checked_sub(HEADER_SIZE)?;
        let array_offset = s.read::<Offset32>()?.to_usize().checked_sub(HEADER_SIZE)?;

        // 'The array can be indexed by completing the left-hand and right-hand class mappings,
        // adding the class values to the address of the subtable,
        // and fetching the kerning value to which the new address points.'

        let left_class =
            crate::kern::get_format2_class(left.0, left_hand_table_offset, self.0).unwrap_or(0);
        let right_class =
            crate::kern::get_format2_class(right.0, right_hand_table_offset, self.0).unwrap_or(0);

        // 'Values within the left-hand offset table should not be less than the kerning array offset.'
        if usize::from(left_class) < array_offset {
            return None;
        }

        // Classes are already premultiplied, so we only need to sum them.
        let index = usize::from(left_class) + usize::from(right_class);
        let value_offset = index.checked_sub(HEADER_SIZE)?;
        Stream::read_at::<i16>(self.0, value_offset)
    }
}

impl core::fmt::Debug for Subtable2<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        write!(f, "Subtable2 {{ ... }}")
    }
}

/// A container of Anchor Points used by [`Subtable4`].
#[derive(Clone, Copy)]
pub struct AnchorPoints<'a>(&'a [u8]);

impl AnchorPoints<'_> {
    /// Returns a mark and current anchor points at action index.
    pub fn get(&self, action_index: u16) -> Option<(u16, u16)> {
        // Each action contains two 16-bit fields, so we must
        // double the action_index to get the correct offset here.
        let offset = usize::from(action_index) * u16::SIZE * 2;
        let mut s = Stream::new_at(self.0, offset)?;
        Some((s.read::<u16>()?, s.read::<u16>()?))
    }
}

impl core::fmt::Debug for AnchorPoints<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        write!(f, "AnchorPoints {{ ... }}")
    }
}

/// A format 4 subtable.
///
/// State Table for Control Point/Anchor Point Positioning.
///
/// Note: I wasn't able to find any fonts that actually use
/// `ControlPointActions` and/or `ControlPointCoordinateActions`,
/// therefore only `AnchorPointActions` is supported.
#[derive(Clone)]
pub struct Subtable4<'a> {
    /// A state table.
    pub state_table: aat::ExtendedStateTable<'a, EntryData>,
    /// Anchor points.
    pub anchor_points: AnchorPoints<'a>,
}

impl<'a> Subtable4<'a> {
    fn parse(number_of_glyphs: NonZeroU16, data: &'a [u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        let state_table = aat::ExtendedStateTable::parse(number_of_glyphs, &mut s)?;
        let flags = s.read::<u32>()?;
        let action_type = ((flags & 0xC0000000) >> 30) as u8;
        let points_offset = usize::num_from(flags & 0x00FFFFFF);

        // We support only Anchor Point Actions.
        if action_type != 1 {
            return None;
        }

        Some(Self {
            state_table,
            anchor_points: AnchorPoints(data.get(points_offset..)?),
        })
    }
}

impl<'a> core::ops::Deref for Subtable4<'a> {
    type Target = aat::ExtendedStateTable<'a, EntryData>;

    fn deref(&self) -> &Self::Target {
        &self.state_table
    }
}

impl core::fmt::Debug for Subtable4<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        write!(f, "Subtable4 {{ ... }}")
    }
}

/// A format 6 subtable.
///
/// Simple Index-based n x m Array of Kerning Values.
#[derive(Clone, Copy)]
pub struct Subtable6<'a> {
    data: &'a [u8],
    number_of_glyphs: NonZeroU16,
}

impl<'a> Subtable6<'a> {
    // TODO: parse actual structure
    fn parse(number_of_glyphs: NonZeroU16, data: &'a [u8]) -> Self {
        Subtable6 {
            number_of_glyphs,
            data,
        }
    }

    /// Returns kerning for a pair of glyphs.
    pub fn glyphs_kerning(&self, left: GlyphId, right: GlyphId) -> Option<i16> {
        use core::convert::TryFrom;

        let mut s = Stream::new(self.data);
        let flags = s.read::<u32>()?;
        s.skip::<u16>(); // row_count
        s.skip::<u16>(); // col_count
                         // All offsets are from the start of the subtable.
        let row_index_table_offset = s.read::<Offset32>()?.to_usize().checked_sub(HEADER_SIZE)?;
        let column_index_table_offset =
            s.read::<Offset32>()?.to_usize().checked_sub(HEADER_SIZE)?;
        let kerning_array_offset = s.read::<Offset32>()?.to_usize().checked_sub(HEADER_SIZE)?;
        let kerning_vector_offset = s.read::<Offset32>()?.to_usize().checked_sub(HEADER_SIZE)?;

        let row_index_table_data = self.data.get(row_index_table_offset..)?;
        let column_index_table_data = self.data.get(column_index_table_offset..)?;
        let kerning_array_data = self.data.get(kerning_array_offset..)?;
        let kerning_vector_data = self.data.get(kerning_vector_offset..)?;

        let has_long_values = flags & 0x00000001 != 0;
        if has_long_values {
            let l: u32 = aat::Lookup::parse(self.number_of_glyphs, row_index_table_data)?
                .value(left)
                .unwrap_or(0) as u32;

            let r: u32 = aat::Lookup::parse(self.number_of_glyphs, column_index_table_data)?
                .value(right)
                .unwrap_or(0) as u32;

            let array_offset = usize::try_from(l + r).ok()?.checked_mul(i32::SIZE)?;
            let vector_offset: u32 = Stream::read_at(kerning_array_data, array_offset)?;

            Stream::read_at(kerning_vector_data, usize::num_from(vector_offset))
        } else {
            let l: u16 = aat::Lookup::parse(self.number_of_glyphs, row_index_table_data)?
                .value(left)
                .unwrap_or(0);

            let r: u16 = aat::Lookup::parse(self.number_of_glyphs, column_index_table_data)?
                .value(right)
                .unwrap_or(0);

            let array_offset = usize::from(l + r).checked_mul(i16::SIZE)?;
            let vector_offset: u16 = Stream::read_at(kerning_array_data, array_offset)?;

            Stream::read_at(kerning_vector_data, usize::from(vector_offset))
        }
    }
}

impl core::fmt::Debug for Subtable6<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        write!(f, "Subtable6 {{ ... }}")
    }
}

/// An extended kerning subtable format.
#[allow(missing_docs)]
#[derive(Clone, Debug)]
pub enum Format<'a> {
    Format0(Subtable0<'a>),
    Format1(Subtable1<'a>),
    Format2(Subtable2<'a>),
    Format4(Subtable4<'a>),
    Format6(Subtable6<'a>),
}

/// A kerning subtable.
#[derive(Clone, Debug)]
pub struct Subtable<'a> {
    /// Indicates that subtable is for horizontal text.
    pub horizontal: bool,
    /// Indicates that subtable is variable.
    pub variable: bool,
    /// Indicates that subtable has a cross-stream values.
    pub has_cross_stream: bool,
    /// Indicates that subtable uses a state machine.
    ///
    /// In this case `glyphs_kerning()` will return `None`.
    pub has_state_machine: bool,
    /// The tuple count.
    ///
    /// This value is only used with variation fonts and should be 0 for all other fonts.
    pub tuple_count: u32,
    /// Subtable format.
    pub format: Format<'a>,
}

impl<'a> Subtable<'a> {
    /// Returns kerning for a pair of glyphs.
    ///
    /// Returns `None` in case of state machine based subtable.
    #[inline]
    pub fn glyphs_kerning(&self, left: GlyphId, right: GlyphId) -> Option<i16> {
        match self.format {
            Format::Format0(ref subtable) => subtable.glyphs_kerning(left, right),
            Format::Format1(_) => None,
            Format::Format2(ref subtable) => subtable.glyphs_kerning(left, right),
            Format::Format4(_) => None,
            Format::Format6(ref subtable) => subtable.glyphs_kerning(left, right),
        }
    }
}

#[derive(Clone, Copy, Debug)]
struct Coverage(u8);

#[rustfmt::skip]
impl Coverage {
    // TODO: use hex
    #[inline] pub fn is_horizontal(self) -> bool { self.0 & (1 << 7) == 0 }
    #[inline] pub fn has_cross_stream(self) -> bool { self.0 & (1 << 6) != 0 }
    #[inline] pub fn is_variable(self) -> bool { self.0 & (1 << 5) != 0 }
}

/// A list of extended kerning subtables.
///
/// The internal data layout is not designed for random access,
/// therefore we're not providing the `get()` method and only an iterator.
#[derive(Clone, Copy)]
pub struct Subtables<'a> {
    /// The number of glyphs from the `maxp` table.
    number_of_glyphs: NonZeroU16,
    /// The total number of tables.
    number_of_tables: u32,
    /// Actual data. Starts right after the `kerx` header.
    data: &'a [u8],
}

impl core::fmt::Debug for Subtables<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        write!(f, "Subtables {{ ... }}")
    }
}

impl<'a> IntoIterator for Subtables<'a> {
    type Item = Subtable<'a>;
    type IntoIter = SubtablesIter<'a>;

    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        SubtablesIter {
            number_of_glyphs: self.number_of_glyphs,
            table_index: 0,
            number_of_tables: self.number_of_tables,
            stream: Stream::new(self.data),
        }
    }
}

/// An iterator over extended kerning subtables.
#[allow(missing_debug_implementations)]
#[derive(Clone)]
pub struct SubtablesIter<'a> {
    /// The number of glyphs from the `maxp` table.
    number_of_glyphs: NonZeroU16,
    /// The current table index.
    table_index: u32,
    /// The total number of tables.
    number_of_tables: u32,
    /// Actual data. Starts right after the `kerx` header.
    stream: Stream<'a>,
}

impl<'a> Iterator for SubtablesIter<'a> {
    type Item = Subtable<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.table_index == self.number_of_tables {
            return None;
        }

        if self.stream.at_end() {
            return None;
        }

        let s = &mut self.stream;

        let table_len = s.read::<u32>()?;
        let coverage = Coverage(s.read::<u8>()?);
        s.skip::<u16>(); // unused
        let raw_format = s.read::<u8>()?;
        let tuple_count = s.read::<u32>()?;

        // Subtract the header size.
        let data_len = usize::num_from(table_len).checked_sub(HEADER_SIZE)?;
        let data = s.read_bytes(data_len)?;

        let format = match raw_format {
            0 => Subtable0::parse(data).map(Format::Format0)?,
            1 => Subtable1::parse(self.number_of_glyphs, data).map(Format::Format1)?,
            2 => Format::Format2(Subtable2(data)),
            4 => Subtable4::parse(self.number_of_glyphs, data).map(Format::Format4)?,
            6 => Format::Format6(Subtable6::parse(self.number_of_glyphs, data)),
            _ => {
                // Unknown format.
                return None;
            }
        };

        self.table_index += 1;

        Some(Subtable {
            horizontal: coverage.is_horizontal(),
            variable: coverage.is_variable(),
            has_cross_stream: coverage.has_cross_stream(),
            has_state_machine: raw_format == 1 || raw_format == 4,
            tuple_count,
            format,
        })
    }
}

/// An [Extended Kerning Table](
/// https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6kerx.html).
#[derive(Clone, Copy, Debug)]
pub struct Table<'a> {
    /// A list of subtables.
    pub subtables: Subtables<'a>,
}

impl<'a> Table<'a> {
    /// Parses a table from raw data.
    ///
    /// `number_of_glyphs` is from the `maxp` table.
    pub fn parse(number_of_glyphs: NonZeroU16, data: &'a [u8]) -> Option<Self> {
        let mut s = Stream::new(data);
        s.skip::<u16>(); // version
        s.skip::<u16>(); // padding
        let number_of_tables = s.read::<u32>()?;
        let subtables = Subtables {
            number_of_glyphs,
            number_of_tables,
            data: s.tail()?,
        };

        Some(Table { subtables })
    }
}