1 /****************************************************************************
2 *
3 * afhints.h
4 *
5 * Auto-fitter hinting routines (specification).
6 *
7 * Copyright (C) 2003-2020 by
8 * David Turner, Robert Wilhelm, and Werner Lemberg.
9 *
10 * This file is part of the FreeType project, and may only be used,
11 * modified, and distributed under the terms of the FreeType project
12 * license, LICENSE.TXT. By continuing to use, modify, or distribute
13 * this file you indicate that you have read the license and
14 * understand and accept it fully.
15 *
16 */
17
18
19 #ifndef AFHINTS_H_
20 #define AFHINTS_H_
21
22 #include "aftypes.h"
23
24 #define xxAF_SORT_SEGMENTS
25
26 FT_BEGIN_HEADER
27
28 /*
29 * The definition of outline glyph hints. These are shared by all
30 * writing system analysis routines (until now).
31 */
32
33 typedef enum AF_Dimension_
34 {
35 AF_DIMENSION_HORZ = 0, /* x coordinates, */
36 /* i.e., vertical segments & edges */
37 AF_DIMENSION_VERT = 1, /* y coordinates, */
38 /* i.e., horizontal segments & edges */
39
40 AF_DIMENSION_MAX /* do not remove */
41
42 } AF_Dimension;
43
44
45 /* hint directions -- the values are computed so that two vectors are */
46 /* in opposite directions iff `dir1 + dir2 == 0' */
47 typedef enum AF_Direction_
48 {
49 AF_DIR_NONE = 4,
50 AF_DIR_RIGHT = 1,
51 AF_DIR_LEFT = -1,
52 AF_DIR_UP = 2,
53 AF_DIR_DOWN = -2
54
55 } AF_Direction;
56
57
58 /*
59 * The following explanations are mostly taken from the article
60 *
61 * Real-Time Grid Fitting of Typographic Outlines
62 *
63 * by David Turner and Werner Lemberg
64 *
65 * https://www.tug.org/TUGboat/Articles/tb24-3/lemberg.pdf
66 *
67 * with appropriate updates.
68 *
69 *
70 * Segments
71 *
72 * `af_{cjk,latin,...}_hints_compute_segments' are the functions to
73 * find segments in an outline.
74 *
75 * A segment is a series of at least two consecutive points that are
76 * approximately aligned along a coordinate axis. The analysis to do
77 * so is specific to a writing system.
78 *
79 *
80 * Edges
81 *
82 * `af_{cjk,latin,...}_hints_compute_edges' are the functions to find
83 * edges.
84 *
85 * As soon as segments are defined, the auto-hinter groups them into
86 * edges. An edge corresponds to a single position on the main
87 * dimension that collects one or more segments (allowing for a small
88 * threshold).
89 *
90 * As an example, the `latin' writing system first tries to grid-fit
91 * edges, then to align segments on the edges unless it detects that
92 * they form a serif.
93 *
94 *
95 * A H
96 * | |
97 * | |
98 * | |
99 * | |
100 * C | | F
101 * +------<-----+ +-----<------+
102 * | B G |
103 * | |
104 * | |
105 * +--------------->------------------+
106 * D E
107 *
108 *
109 * Stems
110 *
111 * Stems are detected by `af_{cjk,latin,...}_hint_edges'.
112 *
113 * Segments need to be `linked' to other ones in order to detect stems.
114 * A stem is made of two segments that face each other in opposite
115 * directions and that are sufficiently close to each other. Using
116 * vocabulary from the TrueType specification, stem segments form a
117 * `black distance'.
118 *
119 * In the above ASCII drawing, the horizontal segments are BC, DE, and
120 * FG; the vertical segments are AB, CD, EF, and GH.
121 *
122 * Each segment has at most one `best' candidate to form a black
123 * distance, or no candidate at all. Notice that two distinct segments
124 * can have the same candidate, which frequently means a serif.
125 *
126 * A stem is recognized by the following condition:
127 *
128 * best segment_1 = segment_2 && best segment_2 = segment_1
129 *
130 * The best candidate is stored in field `link' in structure
131 * `AF_Segment'.
132 *
133 * In the above ASCII drawing, the best candidate for both AB and CD is
134 * GH, while the best candidate for GH is AB. Similarly, the best
135 * candidate for EF and GH is AB, while the best candidate for AB is
136 * GH.
137 *
138 * The detection and handling of stems is dependent on the writing
139 * system.
140 *
141 *
142 * Serifs
143 *
144 * Serifs are detected by `af_{cjk,latin,...}_hint_edges'.
145 *
146 * In comparison to a stem, a serif (as handled by the auto-hinter
147 * module that takes care of the `latin' writing system) has
148 *
149 * best segment_1 = segment_2 && best segment_2 != segment_1
150 *
151 * where segment_1 corresponds to the serif segment (CD and EF in the
152 * above ASCII drawing).
153 *
154 * The best candidate is stored in field `serif' in structure
155 * `AF_Segment' (and `link' is set to NULL).
156 *
157 *
158 * Touched points
159 *
160 * A point is called `touched' if it has been processed somehow by the
161 * auto-hinter. It basically means that it shouldn't be moved again
162 * (or moved only under certain constraints to preserve the already
163 * applied processing).
164 *
165 *
166 * Flat and round segments
167 *
168 * Segments are `round' or `flat', depending on the series of points
169 * that define them. A segment is round if the next and previous point
170 * of an extremum (which can be either a single point or sequence of
171 * points) are both conic or cubic control points. Otherwise, a
172 * segment with an extremum is flat.
173 *
174 *
175 * Strong Points
176 *
177 * Experience has shown that points not part of an edge need to be
178 * interpolated linearly between their two closest edges, even if these
179 * are not part of the contour of those particular points. Typical
180 * candidates for this are
181 *
182 * - angle points (i.e., points where the `in' and `out' direction
183 * differ greatly)
184 *
185 * - inflection points (i.e., where the `in' and `out' angles are the
186 * same, but the curvature changes sign) [currently, such points
187 * aren't handled specially in the auto-hinter]
188 *
189 * `af_glyph_hints_align_strong_points' is the function that takes
190 * care of such situations; it is equivalent to the TrueType `IP'
191 * hinting instruction.
192 *
193 *
194 * Weak Points
195 *
196 * Other points in the outline must be interpolated using the
197 * coordinates of their previous and next unfitted contour neighbours.
198 * These are called `weak points' and are touched by the function
199 * `af_glyph_hints_align_weak_points', equivalent to the TrueType `IUP'
200 * hinting instruction. Typical candidates are control points and
201 * points on the contour without a major direction.
202 *
203 * The major effect is to reduce possible distortion caused by
204 * alignment of edges and strong points, thus weak points are processed
205 * after strong points.
206 */
207
208
209 /* point hint flags */
210 #define AF_FLAG_NONE 0
211
212 /* point type flags */
213 #define AF_FLAG_CONIC ( 1U << 0 )
214 #define AF_FLAG_CUBIC ( 1U << 1 )
215 #define AF_FLAG_CONTROL ( AF_FLAG_CONIC | AF_FLAG_CUBIC )
216
217 /* point touch flags */
218 #define AF_FLAG_TOUCH_X ( 1U << 2 )
219 #define AF_FLAG_TOUCH_Y ( 1U << 3 )
220
221 /* candidates for weak interpolation have this flag set */
222 #define AF_FLAG_WEAK_INTERPOLATION ( 1U << 4 )
223
224 /* the distance to the next point is very small */
225 #define AF_FLAG_NEAR ( 1U << 5 )
226
227
228 /* edge hint flags */
229 #define AF_EDGE_NORMAL 0
230 #define AF_EDGE_ROUND ( 1U << 0 )
231 #define AF_EDGE_SERIF ( 1U << 1 )
232 #define AF_EDGE_DONE ( 1U << 2 )
233 #define AF_EDGE_NEUTRAL ( 1U << 3 ) /* edge aligns to a neutral blue zone */
234
235
236 typedef struct AF_PointRec_* AF_Point;
237 typedef struct AF_SegmentRec_* AF_Segment;
238 typedef struct AF_EdgeRec_* AF_Edge;
239
240
241 typedef struct AF_PointRec_
242 {
243 FT_UShort flags; /* point flags used by hinter */
244 FT_Char in_dir; /* direction of inwards vector */
245 FT_Char out_dir; /* direction of outwards vector */
246
247 FT_Pos ox, oy; /* original, scaled position */
248 FT_Short fx, fy; /* original, unscaled position (in font units) */
249 FT_Pos x, y; /* current position */
250 FT_Pos u, v; /* current (x,y) or (y,x) depending on context */
251
252 AF_Point next; /* next point in contour */
253 AF_Point prev; /* previous point in contour */
254
255 #ifdef FT_DEBUG_AUTOFIT
256 /* track `before' and `after' edges for strong points */
257 AF_Edge before[2];
258 AF_Edge after[2];
259 #endif
260
261 } AF_PointRec;
262
263
264 typedef struct AF_SegmentRec_
265 {
266 FT_Byte flags; /* edge/segment flags for this segment */
267 FT_Char dir; /* segment direction */
268 FT_Short pos; /* position of segment */
269 FT_Short delta; /* deviation from segment position */
270 FT_Short min_coord; /* minimum coordinate of segment */
271 FT_Short max_coord; /* maximum coordinate of segment */
272 FT_Short height; /* the hinted segment height */
273
274 AF_Edge edge; /* the segment's parent edge */
275 AF_Segment edge_next; /* link to next segment in parent edge */
276
277 AF_Segment link; /* (stem) link segment */
278 AF_Segment serif; /* primary segment for serifs */
279 FT_Pos score; /* used during stem matching */
280 FT_Pos len; /* used during stem matching */
281
282 AF_Point first; /* first point in edge segment */
283 AF_Point last; /* last point in edge segment */
284
285 } AF_SegmentRec;
286
287
288 typedef struct AF_EdgeRec_
289 {
290 FT_Short fpos; /* original, unscaled position (in font units) */
291 FT_Pos opos; /* original, scaled position */
292 FT_Pos pos; /* current position */
293
294 FT_Byte flags; /* edge flags */
295 FT_Char dir; /* edge direction */
296 FT_Fixed scale; /* used to speed up interpolation between edges */
297
298 AF_Width blue_edge; /* non-NULL if this is a blue edge */
299 AF_Edge link; /* link edge */
300 AF_Edge serif; /* primary edge for serifs */
301 FT_Int score; /* used during stem matching */
302
303 AF_Segment first; /* first segment in edge */
304 AF_Segment last; /* last segment in edge */
305
306 } AF_EdgeRec;
307
308 #define AF_SEGMENTS_EMBEDDED 18 /* number of embedded segments */
309 #define AF_EDGES_EMBEDDED 12 /* number of embedded edges */
310
311 typedef struct AF_AxisHintsRec_
312 {
313 FT_Int num_segments; /* number of used segments */
314 FT_Int max_segments; /* number of allocated segments */
315 AF_Segment segments; /* segments array */
316 #ifdef AF_SORT_SEGMENTS
317 FT_Int mid_segments;
318 #endif
319
320 FT_Int num_edges; /* number of used edges */
321 FT_Int max_edges; /* number of allocated edges */
322 AF_Edge edges; /* edges array */
323
324 AF_Direction major_dir; /* either vertical or horizontal */
325
326 /* two arrays to avoid allocation penalty */
327 struct
328 {
329 AF_SegmentRec segments[AF_SEGMENTS_EMBEDDED];
330 AF_EdgeRec edges[AF_EDGES_EMBEDDED];
331 } embedded;
332
333
334 } AF_AxisHintsRec, *AF_AxisHints;
335
336
337 #define AF_POINTS_EMBEDDED 96 /* number of embedded points */
338 #define AF_CONTOURS_EMBEDDED 8 /* number of embedded contours */
339
340 typedef struct AF_GlyphHintsRec_
341 {
342 FT_Memory memory;
343
344 FT_Fixed x_scale;
345 FT_Pos x_delta;
346
347 FT_Fixed y_scale;
348 FT_Pos y_delta;
349
350 FT_Int max_points; /* number of allocated points */
351 FT_Int num_points; /* number of used points */
352 AF_Point points; /* points array */
353
354 FT_Int max_contours; /* number of allocated contours */
355 FT_Int num_contours; /* number of used contours */
356 AF_Point* contours; /* contours array */
357
358 AF_AxisHintsRec axis[AF_DIMENSION_MAX];
359
360 FT_UInt32 scaler_flags; /* copy of scaler flags */
361 FT_UInt32 other_flags; /* free for style-specific */
362 /* implementations */
363 AF_StyleMetrics metrics;
364
365 FT_Pos xmin_delta; /* used for warping */
366 FT_Pos xmax_delta;
367
368 /* Two arrays to avoid allocation penalty. */
369 /* The `embedded' structure must be the last element! */
370 struct
371 {
372 AF_Point contours[AF_CONTOURS_EMBEDDED];
373 AF_PointRec points[AF_POINTS_EMBEDDED];
374 } embedded;
375
376 } AF_GlyphHintsRec;
377
378
379 #define AF_HINTS_TEST_SCALER( h, f ) ( (h)->scaler_flags & (f) )
380 #define AF_HINTS_TEST_OTHER( h, f ) ( (h)->other_flags & (f) )
381
382
383 #ifdef FT_DEBUG_AUTOFIT
384
385 #define AF_HINTS_DO_HORIZONTAL( h ) \
386 ( !_af_debug_disable_horz_hints && \
387 !AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_HORIZONTAL ) )
388
389 #define AF_HINTS_DO_VERTICAL( h ) \
390 ( !_af_debug_disable_vert_hints && \
391 !AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_VERTICAL ) )
392
393 #define AF_HINTS_DO_BLUES( h ) ( !_af_debug_disable_blue_hints )
394
395 #else /* !FT_DEBUG_AUTOFIT */
396
397 #define AF_HINTS_DO_HORIZONTAL( h ) \
398 !AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_HORIZONTAL )
399
400 #define AF_HINTS_DO_VERTICAL( h ) \
401 !AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_VERTICAL )
402
403 #define AF_HINTS_DO_BLUES( h ) 1
404
405 #endif /* !FT_DEBUG_AUTOFIT */
406
407
408 #define AF_HINTS_DO_ADVANCE( h ) \
409 !AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_ADVANCE )
410
411 #define AF_HINTS_DO_WARP( h ) \
412 !AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_WARPER )
413
414
415
416 FT_LOCAL( AF_Direction )
417 af_direction_compute( FT_Pos dx,
418 FT_Pos dy );
419
420
421 FT_LOCAL( FT_Error )
422 af_axis_hints_new_segment( AF_AxisHints axis,
423 FT_Memory memory,
424 AF_Segment *asegment );
425
426 FT_LOCAL( FT_Error)
427 af_axis_hints_new_edge( AF_AxisHints axis,
428 FT_Int fpos,
429 AF_Direction dir,
430 FT_Bool top_to_bottom_hinting,
431 FT_Memory memory,
432 AF_Edge *edge );
433
434 FT_LOCAL( void )
435 af_glyph_hints_init( AF_GlyphHints hints,
436 FT_Memory memory );
437
438 FT_LOCAL( void )
439 af_glyph_hints_rescale( AF_GlyphHints hints,
440 AF_StyleMetrics metrics );
441
442 FT_LOCAL( FT_Error )
443 af_glyph_hints_reload( AF_GlyphHints hints,
444 FT_Outline* outline );
445
446 FT_LOCAL( void )
447 af_glyph_hints_save( AF_GlyphHints hints,
448 FT_Outline* outline );
449
450 FT_LOCAL( void )
451 af_glyph_hints_align_edge_points( AF_GlyphHints hints,
452 AF_Dimension dim );
453
454 FT_LOCAL( void )
455 af_glyph_hints_align_strong_points( AF_GlyphHints hints,
456 AF_Dimension dim );
457
458 FT_LOCAL( void )
459 af_glyph_hints_align_weak_points( AF_GlyphHints hints,
460 AF_Dimension dim );
461
462 #ifdef AF_CONFIG_OPTION_USE_WARPER
463 FT_LOCAL( void )
464 af_glyph_hints_scale_dim( AF_GlyphHints hints,
465 AF_Dimension dim,
466 FT_Fixed scale,
467 FT_Pos delta );
468 #endif
469
470 FT_LOCAL( void )
471 af_glyph_hints_done( AF_GlyphHints hints );
472
473 /* */
474
475 #define AF_SEGMENT_LEN( seg ) ( (seg)->max_coord - (seg)->min_coord )
476
477 #define AF_SEGMENT_DIST( seg1, seg2 ) ( ( (seg1)->pos > (seg2)->pos ) \
478 ? (seg1)->pos - (seg2)->pos \
479 : (seg2)->pos - (seg1)->pos )
480
481
482 FT_END_HEADER
483
484 #endif /* AFHINTS_H_ */
485
486
487 /* END */