lib/tahints.h

   1 /* tahints.h */
   2
   3 /*
   4  * Copyright (C) 2011-2014 by Werner Lemberg.
   5  *
   6  * This file is part of the ttfautohint library, and may only be used,
   7  * modified, and distributed under the terms given in `COPYING'.  By
   8  * continuing to use, modify, or distribute this file you indicate that you
   9  * have read `COPYING' and understand and accept it fully.
  10  *
  11  * The file `COPYING' mentioned in the previous paragraph is distributed
  12  * with the ttfautohint library.
  13  */
  14
  15
  16 /* originally file `afhints.h' (2011-Mar-28) from FreeType */
  17
  18 /* heavily modified 2011 by Werner Lemberg <wl@gnu.org> */
  19
  20 #ifndef __TAHINTS_H__
  21 #define __TAHINTS_H__
  22
  23 #include "tatypes.h"
  24
  25 #ifdef __cplusplus
  26 extern "C" {
  27 #endif
  28
  29 #define xxTA_SORT_SEGMENTS
  30
  31
  32 /* the definition of outline glyph hints; these are shared */
  33 /* by all writing system analysis routines (until now) */
  34
  35 typedef enum TA_Dimension_
  36 {
  37   TA_DIMENSION_HORZ = 0, /* x coordinates, i.e. vert. segments & edges */
  38   TA_DIMENSION_VERT = 1, /* y coordinates, i.e. horz. segments & edges */
  39   TA_DIMENSION_MAX /* do not remove */
  40 } TA_Dimension;
  41
  42
  43 /* hint directions -- the values are computed so that two vectors */
  44 /* are in opposite directions iff `dir1 + dir2 == 0' */
  45
  46 typedef enum TA_Direction_
  47 {
  48   TA_DIR_NONE = 4,
  49   TA_DIR_RIGHT = 1,
  50   TA_DIR_LEFT= -1,
  51   TA_DIR_UP = 2,
  52   TA_DIR_DOWN = -2
  53 } TA_Direction;
  54
  55
  56 /*
  57  *  The following explanations are mostly taken from the article
  58  *
  59  *    Real-Time Grid Fitting of Typographic Outlines
  60  *
  61  *  by David Turner and Werner Lemberg
  62  *
  63  *    http://www.tug.org/TUGboat/Articles/tb24-3/lemberg.pdf
  64  *
  65  *  with appropriate updates.
  66  *
  67  *
  68  *  Segments
  69  *
  70  *    `ta_{cjk,latin,...}_hints_compute_segments' are the functions to
  71  *    find segments in an outline.
  72  *
  73  *    A segment is a series of consecutive points that are approximately
  74  *    aligned along a coordinate axis.  The analysis to do so is specific
  75  *    to a writing system.
  76  *
  77  *    A segment must have at least two points, except in the case of
  78  *    `fake' segments that are generated to hint metrics appropriately,
  79  *    and which consist of a single point.
  80  *
  81  *
  82  *  Edges
  83  *
  84  *    `ta_{cjk,latin,...}_hints_compute_edges' are the functions to find
  85  *    edges.
  86  *
  87  *    As soon as segments are defined, the auto-hinter groups them into
  88  *    edges.  An edge corresponds to a single position on the main
  89  *    dimension that collects one or more segments (allowing for a small
  90  *    threshold).
  91  *
  92  *    As an example, the `latin' writing system first tries to grid-fit
  93  *    edges, then to align segments on the edges unless it detects that
  94  *    they form a serif.
  95  *
  96  *
  97  *                      A          H
  98  *                       |        |
  99  *                       |        |
 100  *                       |        |
 101  *                       |        |
 102  *         C             |        |             F
 103  *          +------<-----+        +-----<------+
 104  *          |             B      G             |
 105  *          |                                  |
 106  *          |                                  |
 107  *          +--------------->------------------+
 108  *         D                                    E
 109  *
 110  *
 111  *  Stems
 112  *
 113  *    Stems are detected by `ta_{cjk,latin,...}_hint_edges'.
 114  *
 115  *    Segments need to be `linked' to other ones in order to detect stems.
 116  *    A stem is made of two segments that face each other in opposite
 117  *    directions and that are sufficiently close to each other.  Using
 118  *    vocabulary from the TrueType specification, stem segments form a
 119  *    `black distance'.
 120  *
 121  *    In the above ASCII drawing, the horizontal segments are BC, DE, and
 122  *    FG; the vertical segments are AB, CD, EF, and GH.
 123  *
 124  *    Each segment has at most one `best' candidate to form a black
 125  *    distance, or no candidate at all.  Notice that two distinct segments
 126  *    can have the same candidate, which frequently means a serif.
 127  *
 128  *    A stem is recognized by the following condition:
 129  *
 130  *      best segment_1 = segment_2 && best segment_2 = segment_1
 131  *
 132  *    The best candidate is stored in field `link' in structure
 133  *    `TA_Segment'.
 134  *
 135  *    In the above ASCII drawing, the best candidate for both AB and CD is
 136  *    GH, while the best candidate for GH is AB.  Similarly, the best
 137  *    candidate for EF and GH is AB, while the best candidate for AB is
 138  *    GH.
 139  *
 140  *    The detection and handling of stems is dependent on the writing
 141  *    system.
 142  *
 143  *
 144  *  Serifs
 145  *
 146  *    Serifs are detected by `ta_{cjk,latin,...}_hint_edges'.
 147  *
 148  *    In comparison to a stem, a serif (as handled by the auto-hinter
 149  *    module which takes care of the `latin' writing system) has
 150  *
 151  *      best segment_1 = segment_2 && best segment_2 != segment_1
 152  *
 153  *    where segment_1 corresponds to the serif segment (CD and EF in the
 154  *    above ASCII drawing).
 155  *
 156  *    The best candidate is stored in field `serif' in structure
 157  *    `TA_Segment' (and `link' is set to NULL).
 158  *
 159  *
 160  *  Touched points
 161  *
 162  *    A point is called `touched' if it has been processed somehow by the
 163  *    auto-hinter.  It basically means that it shouldn't be moved again
 164  *    (or moved only under certain constraints to preserve the already
 165  *    applied processing).
 166  *
 167  *
 168  *  Flat and round segments
 169  *
 170  *    Segments are `round' or `flat', depending on the series of points
 171  *    that define them.  A segment is round if the next and previous point
 172  *    of an extremum (which can be either a single point or sequence of
 173  *    points) are both conic or cubic control points.  Otherwise, a
 174  *    segment with an extremum is flat.
 175  *
 176  *
 177  *  Strong Points
 178  *
 179  *    Experience has shown that points which are not part of an edge need
 180  *    to be interpolated linearly between their two closest edges, even if
 181  *    these are not part of the contour of those particular points.
 182  *    Typical candidates for this are
 183  *
 184  *    - angle points (i.e., points where the `in' and `out' direction
 185  *      differ greatly)
 186  *
 187  *    - inflection points (i.e., where the `in' and `out' angles are the
 188  *      same, but the curvature changes sign) [currently, such points
 189  *      aren't handled in the auto-hinter]
 190  *
 191  *    `ta_glyph_hints_align_strong_points' is the function which takes
 192  *    care of such situations; it is equivalent to the TrueType `IP'
 193  *    hinting instruction.
 194  *
 195  *
 196  *  Weak Points
 197  *
 198  *    Other points in the outline must be interpolated using the
 199  *    coordinates of their previous and next unfitted contour neighbours.
 200  *    These are called `weak points' and are touched by the function
 201  *    `ta_glyph_hints_align_weak_points', equivalent to the TrueType `IUP'
 202  *    hinting instruction.  Typical candidates are control points and
 203  *    points on the contour without a major direction.
 204  *
 205  *    The major effect is to reduce possible distortion caused by
 206  *    alignment of edges and strong points, thus weak points are processed
 207  *    after strong points.
 208  */
 209
 210
 211 /* point hint flags */
 212 #define TA_FLAG_NONE 0
 213
 214 /* point type flags */
 215 #define TA_FLAG_CONIC (1 << 0)
 216 #define TA_FLAG_CUBIC (1 << 1)
 217 #define TA_FLAG_CONTROL (TA_FLAG_CONIC | TA_FLAG_CUBIC)
 218
 219 /* point extremum flags */
 220 #define TA_FLAG_EXTREMA_X (1 << 2)
 221 #define TA_FLAG_EXTREMA_Y (1 << 3)
 222
 223 /* point roundness flags */
 224 #define TA_FLAG_ROUND_X (1 << 4)
 225 #define TA_FLAG_ROUND_Y (1 << 5)
 226
 227 /* point touch flags */
 228 #define TA_FLAG_TOUCH_X (1 << 6)
 229 #define TA_FLAG_TOUCH_Y (1 << 7)
 230
 231 /* candidates for weak interpolation have this flag set */
 232 #define TA_FLAG_WEAK_INTERPOLATION (1 << 8)
 233
 234 /* all inflection points in the outline have this flag set */
 235 #define TA_FLAG_INFLECTION (1 << 9)
 236
 237
 238 /* edge hint flags */
 239 #define TA_EDGE_NORMAL 0
 240 #define TA_EDGE_ROUND (1 << 0)
 241 #define TA_EDGE_SERIF (1 << 1)
 242 #define TA_EDGE_DONE (1 << 2)
 243 #define TA_EDGE_NEUTRAL (1 << 3)
 244
 245
 246 typedef struct TA_PointRec_* TA_Point;
 247 typedef struct TA_SegmentRec_* TA_Segment;
 248 typedef struct TA_EdgeRec_* TA_Edge;
 249
 250
 251 typedef struct TA_PointRec_
 252 {
 253   FT_UShort flags; /* point flags used by hinter */
 254   FT_Char in_dir; /* direction of inwards vector */
 255   FT_Char out_dir; /* direction of outwards vector */
 256
 257   FT_Pos ox, oy; /* original, scaled position */
 258   FT_Short fx, fy; /* original, unscaled position (in font units) */
 259   FT_Pos x, y; /* current position */
 260   FT_Pos u, v; /* current (x,y) or (y,x) depending on context */
 261
 262   TA_Point next; /* next point in contour */
 263   TA_Point prev; /* previous point in contour */
 264 } TA_PointRec;
 265
 266
 267 typedef struct TA_SegmentRec_
 268 {
 269   FT_Byte flags; /* edge/segment flags for this segment */
 270   FT_Char dir; /* segment direction */
 271   FT_Short pos; /* position of segment */
 272   FT_Short min_coord; /* minimum coordinate of segment */
 273   FT_Short max_coord; /* maximum coordinate of segment */
 274   FT_Short height; /* the hinted segment height */
 275
 276   TA_Edge edge; /* the segment's parent edge */
 277   TA_Segment edge_next; /* link to next segment in parent edge */
 278
 279   TA_Segment link; /* (stem) link segment */
 280   TA_Segment serif; /* primary segment for serifs */
 281   FT_Pos num_linked; /* number of linked segments */
 282   FT_Pos score; /* used during stem matching */
 283   FT_Pos len; /* used during stem matching */
 284
 285   TA_Point first; /* first point in edge segment */
 286   TA_Point last; /* last point in edge segment */
 287 } TA_SegmentRec;
 288
 289
 290 typedef struct TA_EdgeRec_
 291 {
 292   FT_Short fpos; /* original, unscaled position (in font units) */
 293   FT_Pos opos; /* original, scaled position */
 294   FT_Pos pos; /* current position */
 295
 296   FT_Byte flags; /* edge flags */
 297   FT_Char dir; /* edge direction */
 298   FT_Fixed scale; /* used to speed up interpolation between edges */
 299
 300   TA_Width blue_edge; /* non-NULL if this is a blue edge */
 301   FT_UInt best_blue_idx; /* for the hinting recorder callback */
 302   FT_Bool best_blue_is_shoot; /* for the hinting recorder callback */
 303
 304   TA_Edge link; /* link edge */
 305   TA_Edge serif; /* primary edge for serifs */
 306   FT_Short num_linked; /* number of linked edges */
 307   FT_Int score; /* used during stem matching */
 308
 309   TA_Segment first; /* first segment in edge */
 310   TA_Segment last; /* last segment in edge */
 311 } TA_EdgeRec;
 312
 313
 314 typedef struct TA_AxisHintsRec_
 315 {
 316   FT_Int num_segments; /* number of used segments */
 317   FT_Int max_segments; /* number of allocated segments */
 318   TA_Segment segments; /* segments array */
 319 #ifdef TA_SORT_SEGMENTS
 320   FT_Int mid_segments;
 321 #endif
 322
 323   FT_Int num_edges; /* number of used edges */
 324   FT_Int max_edges; /* number of allocated edges */
 325   TA_Edge edges; /* edges array */
 326
 327   TA_Direction major_dir; /* either vertical or horizontal */
 328 } TA_AxisHintsRec, *TA_AxisHints;
 329
 330
 331 typedef enum TA_Action_
 332 {
 333   /* point actions */
 334
 335   ta_ip_before,
 336   ta_ip_after,
 337   ta_ip_on,
 338   ta_ip_between,
 339
 340   /* edge actions */
 341
 342   ta_blue,
 343   ta_blue_anchor,
 344
 345   ta_anchor,
 346   ta_anchor_serif,
 347   ta_anchor_round,
 348   ta_anchor_round_serif,
 349
 350   ta_adjust,
 351   ta_adjust_serif,
 352   ta_adjust_round,
 353   ta_adjust_round_serif,
 354   ta_adjust_bound,
 355   ta_adjust_bound_serif,
 356   ta_adjust_bound_round,
 357   ta_adjust_bound_round_serif,
 358
 359   ta_link,
 360   ta_link_serif,
 361   ta_link_round,
 362   ta_link_round_serif,
 363
 364   ta_stem,
 365   ta_stem_serif,
 366   ta_stem_round,
 367   ta_stem_round_serif,
 368   ta_stem_bound,
 369   ta_stem_bound_serif,
 370   ta_stem_bound_round,
 371   ta_stem_bound_round_serif,
 372
 373   ta_serif,
 374   ta_serif_lower_bound,
 375   ta_serif_upper_bound,
 376   ta_serif_upper_lower_bound,
 377
 378   ta_serif_anchor,
 379   ta_serif_anchor_lower_bound,
 380   ta_serif_anchor_upper_bound,
 381   ta_serif_anchor_upper_lower_bound,
 382
 383   ta_serif_link1,
 384   ta_serif_link1_lower_bound,
 385   ta_serif_link1_upper_bound,
 386   ta_serif_link1_upper_lower_bound,
 387
 388   ta_serif_link2,
 389   ta_serif_link2_lower_bound,
 390   ta_serif_link2_upper_bound,
 391   ta_serif_link2_upper_lower_bound,
 392
 393   ta_bound
 394 } TA_Action;
 395
 396
 397 typedef void
 398 (*TA_Hints_Recorder)(TA_Action action,
 399                      TA_GlyphHints hints,
 400                      TA_Dimension dim,
 401                      void* arg1, /* TA_Point or TA_Edge */
 402                      TA_Edge arg2,
 403                      TA_Edge arg3,
 404                      TA_Edge lower_bound,
 405                      TA_Edge upper_bound);
 406
 407 typedef struct TA_GlyphHintsRec_
 408 {
 409   FT_Fixed x_scale;
 410   FT_Pos x_delta;
 411
 412   FT_Fixed y_scale;
 413   FT_Pos y_delta;
 414
 415   FT_Int max_points; /* number of allocated points */
 416   FT_Int num_points; /* number of used points */
 417   TA_Point points; /* points array */
 418
 419   FT_Int max_contours; /* number of allocated contours */
 420   FT_Int num_contours; /* number of used contours */
 421   TA_Point* contours; /* contours array */
 422
 423   TA_AxisHintsRec axis[TA_DIMENSION_MAX];
 424
 425   FT_UInt32 scaler_flags; /* copy of scaler flags */
 426   FT_UInt32 other_flags; /* free for style-specific implementations */
 427   TA_StyleMetrics metrics;
 428
 429   FT_Pos xmin_delta; /* used for warping */
 430   FT_Pos xmax_delta;
 431
 432   TA_Hints_Recorder recorder;
 433   void* user;
 434 } TA_GlyphHintsRec;
 435
 436
 437 #define TA_HINTS_TEST_SCALER(h, f) \
 438           ((h)->scaler_flags & (f))
 439 #define TA_HINTS_TEST_OTHER(h, f) \
 440           ((h)->other_flags & (f))
 441
 442
 443 #ifdef TA_DEBUG
 444
 445 #define TA_HINTS_DO_HORIZONTAL(h) \
 446           (!_ta_debug_disable_horz_hints \
 447            && !TA_HINTS_TEST_SCALER(h, TA_SCALER_FLAG_NO_HORIZONTAL))
 448
 449 #define TA_HINTS_DO_VERTICAL(h) \
 450           (!_ta_debug_disable_vert_hints \
 451            && !TA_HINTS_TEST_SCALER(h, TA_SCALER_FLAG_NO_VERTICAL))
 452
 453 #define TA_HINTS_DO_ADVANCE(h) \
 454           !TA_HINTS_TEST_SCALER(h, TA_SCALER_FLAG_NO_ADVANCE)
 455
 456 #define TA_HINTS_DO_BLUES(h) \
 457           (!_ta_debug_disable_blue_hints)
 458
 459 #else /* !TA_DEBUG */
 460
 461 #define TA_HINTS_DO_HORIZONTAL(h) \
 462           !TA_HINTS_TEST_SCALER(h, TA_SCALER_FLAG_NO_HORIZONTAL)
 463
 464 #define TA_HINTS_DO_VERTICAL(h) \
 465           !TA_HINTS_TEST_SCALER(h, TA_SCALER_FLAG_NO_VERTICAL)
 466
 467 #define TA_HINTS_DO_ADVANCE(h) \
 468           !TA_HINTS_TEST_SCALER(h, TA_SCALER_FLAG_NO_ADVANCE)
 469
 470 #define TA_HINTS_DO_BLUES(h) \
 471           1
 472
 473 #endif /* !TA_DEBUG */
 474
 475
 476 TA_Direction
 477 ta_direction_compute(FT_Pos dx,
 478                      FT_Pos dy);
 479
 480
 481 FT_Error
 482 ta_axis_hints_new_segment(TA_AxisHints axis,
 483                           TA_Segment* asegment);
 484
 485 FT_Error
 486 ta_axis_hints_new_edge(TA_AxisHints axis,
 487                        FT_Int fpos,
 488                        TA_Direction dir,
 489                        TA_Edge* edge);
 490
 491 #ifdef TA_DEBUG
 492 void
 493 ta_glyph_hints_dump_points(TA_GlyphHints hints);
 494
 495 void
 496 ta_glyph_hints_dump_segments(TA_GlyphHints hints);
 497
 498 void
 499 ta_glyph_hints_dump_edges(TA_GlyphHints hints);
 500 #endif
 501
 502 void
 503 ta_glyph_hints_init(TA_GlyphHints hints);
 504
 505 void
 506 ta_glyph_hints_rescale(TA_GlyphHints hints,
 507                        TA_StyleMetrics metrics);
 508
 509 FT_Error
 510 ta_glyph_hints_reload(TA_GlyphHints hints,
 511                       FT_Outline* outline);
 512
 513 void
 514 ta_glyph_hints_save(TA_GlyphHints hints,
 515                     FT_Outline* outline);
 516
 517 void
 518 ta_glyph_hints_align_edge_points(TA_GlyphHints hints,
 519                                  TA_Dimension dim);
 520
 521 void
 522 ta_glyph_hints_align_strong_points(TA_GlyphHints hints,
 523                                    TA_Dimension dim);
 524
 525 void
 526 ta_glyph_hints_align_weak_points(TA_GlyphHints hints,
 527                                  TA_Dimension dim);
 528
 529 #ifdef TA_CONFIG_OPTION_USE_WARPER
 530 void
 531 ta_glyph_hints_scale_dim(TA_GlyphHints hints,
 532                          TA_Dimension dim,
 533                          FT_Fixed scale,
 534                          FT_Pos delta);
 535 #endif
 536
 537 void
 538 ta_glyph_hints_done(TA_GlyphHints hints);
 539
 540
 541 #define TA_SEGMENT_LEN(seg) \
 542           ((seg)->max_coord - (seg)->min_coord)
 543
 544 #define TA_SEGMENT_DIST(seg1, seg2) \
 545           (((seg1)->pos > (seg2)->pos) ? (seg1)->pos - (seg2)->pos \
 546                                        : (seg2)->pos - (seg1)->pos)
 547
 548 #ifdef __cplusplus
 549 } /* extern "C" */
 550 #endif
 551
 552 #endif /* __TAHINTS_H__ */
 553
 554
 555 /* end of tahints.h */