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