sharkk/corvette public

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

package font

// ============================================================================
// KERNING
// ============================================================================

// Get the length of the kerning table (number of entries)
get_kerning_table_length :: proc(info: ^Font_Info) -> i32 {
	data := info.data[info.kern:]

	// we only look at the first table. it must be 'horizontal' and format 0.
	if info.kern == 0 {
		return 0
	}
	if ttUSHORT(data[2:]) < 1 { // number of tables, need at least 1
		return 0
	}
	if ttUSHORT(data[8:]) != 1 { // horizontal flag must be set in format
		return 0
	}

	return i32(ttUSHORT(data[10:]))
}

// Get the complete kerning table
// Returns how many entries were written (never more than table_length)
get_kerning_table :: proc(info: ^Font_Info, table: [^]Kerning_Entry, table_length: i32) -> i32 {
	data := info.data[info.kern:]

	// we only look at the first table. it must be 'horizontal' and format 0.
	if info.kern == 0 {
		return 0
	}
	if ttUSHORT(data[2:]) < 1 { // number of tables, need at least 1
		return 0
	}
	if ttUSHORT(data[8:]) != 1 { // horizontal flag must be set in format
		return 0
	}

	length := i32(ttUSHORT(data[10:]))
	if table_length < length {
		length = table_length
	}

	for k: i32 = 0; k < length; k += 1 {
		table[k].glyph1 = i32(ttUSHORT(data[18 + k*6:]))
		table[k].glyph2 = i32(ttUSHORT(data[20 + k*6:]))
		table[k].advance = i32(ttSHORT(data[22 + k*6:]))
	}

	return length
}

// Private: Get kerning advance from kern table using binary search
@(private)
get_glyph_kern_info_advance :: proc(info: ^Font_Info, glyph1: i32, glyph2: i32) -> i32 {
	data := info.data[info.kern:]

	// we only look at the first table. it must be 'horizontal' and format 0.
	if info.kern == 0 {
		return 0
	}
	if ttUSHORT(data[2:]) < 1 { // number of tables, need at least 1
		return 0
	}
	if ttUSHORT(data[8:]) != 1 { // horizontal flag must be set in format
		return 0
	}

	l: i32 = 0
	r: i32 = i32(ttUSHORT(data[10:])) - 1
	needle := u32(glyph1) << 16 | u32(glyph2)

	for l <= r {
		m := (l + r) >> 1
		straw := ttULONG(data[18 + m*6:]) // note: unaligned read
		if needle < straw {
			r = m - 1
		} else if needle > straw {
			l = m + 1
		} else {
			return i32(ttSHORT(data[22 + m*6:]))
		}
	}
	return 0
}

// Private: Get coverage index from a GPOS coverage table
@(private)
get_coverage_index :: proc(coverage_table: [^]u8, glyph: i32) -> i32 {
	coverage_format := ttUSHORT(coverage_table)

	switch coverage_format {
	case 1:
		glyph_count := i32(ttUSHORT(coverage_table[2:]))

		// Binary search
		l: i32 = 0
		r: i32 = glyph_count - 1
		needle := glyph
		for l <= r {
			glyph_array := coverage_table[4:]
			m := (l + r) >> 1
			glyph_id := i32(ttUSHORT(glyph_array[2 * m:]))
			straw := glyph_id
			if needle < straw {
				r = m - 1
			} else if needle > straw {
				l = m + 1
			} else {
				return m
			}
		}

	case 2:
		range_count := i32(ttUSHORT(coverage_table[2:]))
		range_array := coverage_table[4:]

		// Binary search
		l: i32 = 0
		r: i32 = range_count - 1
		needle := glyph
		for l <= r {
			m := (l + r) >> 1
			range_record := range_array[6 * m:]
			straw_start := i32(ttUSHORT(range_record))
			straw_end := i32(ttUSHORT(range_record[2:]))
			if needle < straw_start {
				r = m - 1
			} else if needle > straw_end {
				l = m + 1
			} else {
				start_coverage_index := i32(ttUSHORT(range_record[4:]))
				return start_coverage_index + glyph - straw_start
			}
		}

	case:
		return -1 // unsupported
	}

	return -1
}

// Private: Get glyph class from a GPOS class definition table
@(private)
get_glyph_class :: proc(class_def_table: [^]u8, glyph: i32) -> i32 {
	class_def_format := ttUSHORT(class_def_table)

	switch class_def_format {
	case 1:
		start_glyph_id := i32(ttUSHORT(class_def_table[2:]))
		glyph_count := i32(ttUSHORT(class_def_table[4:]))
		class_def1_value_array := class_def_table[6:]

		if glyph >= start_glyph_id && glyph < start_glyph_id + glyph_count {
			return i32(ttUSHORT(class_def1_value_array[2 * (glyph - start_glyph_id):]))
		}

	case 2:
		class_range_count := i32(ttUSHORT(class_def_table[2:]))
		class_range_records := class_def_table[4:]

		// Binary search
		l: i32 = 0
		r: i32 = class_range_count - 1
		needle := glyph
		for l <= r {
			m := (l + r) >> 1
			class_range_record := class_range_records[6 * m:]
			straw_start := i32(ttUSHORT(class_range_record))
			straw_end := i32(ttUSHORT(class_range_record[2:]))
			if needle < straw_start {
				r = m - 1
			} else if needle > straw_end {
				l = m + 1
			} else {
				return i32(ttUSHORT(class_range_record[4:]))
			}
		}

	case:
		return -1 // Unsupported definition type
	}

	// "All glyphs not assigned to a class fall into class 0". (OpenType spec)
	return 0
}

// Count bits set in a ValueFormat field to determine ValueRecord size
@(private)
value_record_size :: proc(format: u16) -> i32 {
	// Each bit in the format field indicates a 16-bit value is present
	count: i32 = 0
	f := format
	for f != 0 {
		count += i32(f & 1)
		f >>= 1
	}
	return count * 2 // each field is 2 bytes
}

// Extract XAdvance from a ValueRecord given its format
@(private)
value_record_x_advance :: proc(record: [^]u8, format: u16) -> i32 {
	if format & 4 == 0 do return 0 // XAdvance not present
	// XAdvance is the 3rd field (bit 2). Count preceding fields.
	offset: i32 = 0
	if format & 1 != 0 do offset += 2 // XPlacement
	if format & 2 != 0 do offset += 2 // YPlacement
	return i32(ttSHORT(record[offset:]))
}

// Private: Get kerning advance from GPOS table
@(private)
get_glyph_gpos_info_advance :: proc(info: ^Font_Info, glyph1: i32, glyph2: i32) -> i32 {
	if info.gpos == 0 {
		return 0
	}

	data := info.data[info.gpos:]

	if ttUSHORT(data) != 1 { // Major version 1
		return 0
	}
	minor_version := ttUSHORT(data[2:])
	if minor_version != 0 && minor_version != 1 {
		return 0
	}

	lookup_list_offset := ttUSHORT(data[8:])
	lookup_list := data[lookup_list_offset:]
	lookup_count := i32(ttUSHORT(lookup_list))

	for i: i32 = 0; i < lookup_count; i += 1 {
		lookup_offset := ttUSHORT(lookup_list[2 + 2*i:])
		lookup_table := lookup_list[lookup_offset:]

		lookup_type := i32(ttUSHORT(lookup_table))
		sub_table_count := i32(ttUSHORT(lookup_table[4:]))
		sub_table_offsets := lookup_table[6:]

		for sti: i32 = 0; sti < sub_table_count; sti += 1 {
			subtable_offset := ttUSHORT(sub_table_offsets[2*sti:])
			table := lookup_table[subtable_offset:]
			actual_type := lookup_type

			// Handle Extension Positioning (Type 9)
			if lookup_type == 9 {
				ext_format := ttUSHORT(table)
				if ext_format != 1 do continue
				actual_type = i32(ttUSHORT(table[2:]))
				table = table[ttULONG(table[4:]):]
			}

			if actual_type != 2 do continue // Only handle Pair Adjustment

			pos_format := ttUSHORT(table)
			coverage_offset := i32(ttUSHORT(table[2:]))
			coverage_index := get_coverage_index(table[coverage_offset:], glyph1)
			if coverage_index == -1 do continue

			value_format1 := ttUSHORT(table[4:])
			value_format2 := ttUSHORT(table[6:])
			vr1_size := value_record_size(value_format1)
			vr2_size := value_record_size(value_format2)

			switch pos_format {
			case 1: // Individual pair sets
				pair_set_count := i32(ttUSHORT(table[8:]))
				if coverage_index >= pair_set_count do continue
				pair_pos_offset := i32(ttUSHORT(table[10 + 2*coverage_index:]))
				pair_value_table := table[pair_pos_offset:]
				pair_value_count := i32(ttUSHORT(pair_value_table))
				pair_value_array := pair_value_table[2:]

				record_size := 2 + vr1_size + vr2_size // secondGlyph + vr1 + vr2
				needle := glyph2
				l: i32 = 0
				r := pair_value_count - 1
				for l <= r {
					m := (l + r) >> 1
					pair_value := pair_value_array[record_size * m:]
					second_glyph := i32(ttUSHORT(pair_value))
					if needle < second_glyph {
						r = m - 1
					} else if needle > second_glyph {
						l = m + 1
					} else {
						return value_record_x_advance(pair_value[2:], value_format1)
					}
				}

			case 2: // Class-based pairs
				class_def1_offset := i32(ttUSHORT(table[8:]))
				class_def2_offset := i32(ttUSHORT(table[10:]))
				glyph1class := get_glyph_class(table[class_def1_offset:], glyph1)
				glyph2class := get_glyph_class(table[class_def2_offset:], glyph2)

				class1_count := i32(ttUSHORT(table[12:]))
				class2_count := i32(ttUSHORT(table[14:]))

				if glyph1class < 0 || glyph1class >= class1_count do continue
				if glyph2class < 0 || glyph2class >= class2_count do continue

				record_pair_size := vr1_size + vr2_size
				class1_records := table[16:]
				offset := glyph1class * class2_count * record_pair_size + glyph2class * record_pair_size
				return value_record_x_advance(class1_records[offset:], value_format1)
			}
		}
	}

	return 0
}

// Get kerning advance for a glyph pair
// Uses cache for O(1) repeated lookups. GPOS takes priority over kern.
get_glyph_kern_advance :: proc(info: ^Font_Info, g1: i32, g2: i32) -> i32 {
	if info.gpos == 0 && info.kern == 0 do return 0

	key := (u64(u32(g1)) << 32) | u64(u32(g2))

	// Check cache
	if info.kern_cache_ready {
		if val, ok := info.kern_cache[key]; ok {
			return val
		}
	}

	// Compute
	x_advance: i32 = 0
	if info.gpos != 0 {
		x_advance = get_glyph_gpos_info_advance(info, g1, g2)
	} else if info.kern != 0 {
		x_advance = get_glyph_kern_info_advance(info, g1, g2)
	}

	// Store in cache
	if !info.kern_cache_ready {
		info.kern_cache = make(map[u64]i32)
		info.kern_cache_ready = true
	}
	info.kern_cache[key] = x_advance

	return x_advance
}

// Get kerning advance for a codepoint pair
get_codepoint_kern_advance :: proc(info: ^Font_Info, ch1: i32, ch2: i32) -> i32 {
	if info.kern == 0 && info.gpos == 0 { // if no kerning table, don't waste time looking up both codepoint->glyphs
		return 0
	}
	return get_glyph_kern_advance(info, find_glyph_index(info, ch1), find_glyph_index(info, ch2))
}