cpml/cpml-segment.c

   1 /* CPML - Cairo Path Manipulation Library
   2  * Copyright (C) 2008, 2009  Nicola Fontana <ntd at entidi.it>
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this library; if not, write to the
  16  * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  17  * Boston, MA  02110-1301, USA.
  18  */
  19
  20
  21 /**
  22  * SECTION:cpml-segment
  23  * @Section_Id:CpmlSegment
  24  * @title: CpmlSegment
  25  * @short_description: Contiguous segment that can be a fragment
  26  *                     or a whole cairo path
  27  *
  28  * A segment is a single contiguous line got from a cairo path. The
  29  * CPML library relies on one assumption to let the data be independent
  30  * from the current point (and thus from the cairo context): any segment
  31  * MUST be preceded by at least one %CAIRO_PATH_MOVE_TO primitive.
  32  * This means a valid segment in cairo could be rejected by CPML.
  33  *
  34  * #CpmlSegment provides an unobtrusive way to access a cairo path.
  35  * This means #CpmlSegment itsself does not hold any coordinates but
  36  * instead a bunch of pointers to the original #cairo_path_t struct:
  37  * modifying data throught this struct also changes the original path.
  38  *
  39  * Every #CpmlPath struct can contain more than one segment: the CPML
  40  * library provides iteration APIs to browse the segments of a path.
  41  * Use cpml_segment_reset() to reset the iterator at the start of the
  42  * cairo path (will point the first segment) and cpml_segment_next()
  43  * to get the next segment. Getting the previous segment is not provided
  44  * as the underlying cairo struct is not accessible in reverse order.
  45  *
  46  * When initialized, #CpmlSegment yet refers to the first segment so
  47  * the initial reset is not required.
  48  **/
  49
  50 /**
  51  * CpmlPath:
  52  *
  53  * This is another name for the #cairo_path_t type. Although phisically
  54  * they are the same struct, #CpmlPath conceptually embodies an important
  55  * difference: it is a cairo path that can embed %CAIRO_PATH_ARC_TO
  56  * primitives. This is not a native cairo primitive and having two
  57  * different data types is a good way to make clear when a function
  58  * expect or not embedded arc-to primitives.
  59  **/
  60
  61 /**
  62  * CpmlSegment:
  63  * @path:     the source #CpmlPath struct
  64  * @data:     the data points of the segment; the first primitive
  65  *            will always be a %CAIRO_PATH_MOVE_TO
  66  * @num_data: size of @data
  67  *
  68  * This is an unobtrusive struct to identify a segment inside a
  69  * cairo path. Unobtrusive means that the real coordinates are
  70  * still stored in @path: CpmlSegment only provides a way to
  71  * access them.
  72  **/
  73
  74
  75 #include "cpml-segment.h"
  76 #include "cpml-primitive.h"
  77 #include "cpml-line.h"
  78 #include "cpml-curve.h"
  79 #include "cpml-pair.h"
  80 #include "cpml-alloca.h"
  81
  82 #include <stdio.h>
  83 #include <string.h>
  84
  85 static cairo_bool_t     normalize               (CpmlSegment       *segment);
  86 static cairo_bool_t     ensure_one_move_to      (CpmlSegment       *segment);
  87 static void             reshape                 (CpmlSegment       *segment);
  88
  89
  90 /**
  91  * cpml_segment_from_cairo:
  92  * @segment: a #CpmlSegment
  93  * @path: the source #CpmlPath
  94  *
  95  * Builds a CpmlSegment from a #CpmlPath structure. This operation
  96  * involves stripping the leading %CAIRO_PATH_MOVE_TO primitives and
  97  * setting the internal segment structure accordling. A pointer to the
  98  * source cairo path is kept.
  99  *
 100  * This function will fail if @path is null, empty or if its
 101  * <structfield>status</structfield> member is not %CAIRO_STATUS_SUCCESS.
 102  * Also, the first primitive must be a %CAIRO_PATH_MOVE_TO, so no
 103  * dependency on the cairo context is needed.
 104  *
 105  * Return value: 1 on success, 0 on errors
 106  **/
 107 cairo_bool_t
 108 cpml_segment_from_cairo(CpmlSegment *segment, CpmlPath *path)
 109 {
 110     /* The cairo path should be defined and in a perfect state */
 111     if (path == NULL || path->num_data == 0 ||
 112         path->status != CAIRO_STATUS_SUCCESS)
 113         return 0;
 114
 115     segment->path = path;
 116     segment->data = path->data;
 117     segment->num_data = path->num_data;
 118
 119     return normalize(segment);
 120 }
 121
 122 /**
 123  * cpml_segment_copy:
 124  * @segment: a #CpmlSegment
 125  * @src: the source segment to copy
 126  *
 127  * Makes a shallow copy of @src into @segment.
 128  *
 129  * Return value: @segment or %NULL on errors
 130  **/
 131 CpmlSegment *
 132 cpml_segment_copy(CpmlSegment *segment, const CpmlSegment *src)
 133 {
 134     if (segment == NULL || src == NULL)
 135         return NULL;
 136
 137     return memcpy(segment, src, sizeof(CpmlSegment));
 138 }
 139
 140
 141 /**
 142  * cpml_segment_reset:
 143  * @segment: a #CpmlSegment
 144  *
 145  * Modifies @segment to point to the first segment of the source cairo path.
 146  **/
 147 void
 148 cpml_segment_reset(CpmlSegment *segment)
 149 {
 150     segment->data = segment->path->data;
 151     segment->num_data = segment->path->num_data;
 152     normalize(segment);
 153 }
 154
 155 /**
 156  * cpml_segment_next:
 157  * @segment: a #CpmlSegment
 158  *
 159  * Modifies @segment to point to the next segment of the source cairo path.
 160  *
 161  * Return value: 1 on success, 0 if no next segment found or errors
 162  **/
 163 cairo_bool_t
 164 cpml_segment_next(CpmlSegment *segment)
 165 {
 166     int rest = segment->path->num_data - segment->num_data +
 167         segment->path->data - segment->data;
 168
 169     if (rest <= 0)
 170         return 0;
 171
 172     segment->data += segment->num_data;
 173     segment->num_data = rest;
 174
 175     return normalize(segment);
 176 }
 177
 178
 179 /**
 180  * cpml_segment_length:
 181  * @segment: a #CpmlSegment
 182  *
 183  * Gets the whole length of @segment.
 184  *
 185  * Returns: the requested length
 186  **/
 187 double
 188 cpml_segment_length(const CpmlSegment *segment)
 189 {
 190     CpmlPrimitive primitive;
 191     double length;
 192
 193     cpml_primitive_from_segment(&primitive, (CpmlSegment *) segment);
 194     length = 0;
 195
 196     do {
 197         length += cpml_primitive_length(&primitive);
 198     } while (cpml_primitive_next(&primitive));
 199
 200     return length;
 201 }
 202
 203 /**
 204  * cpml_segment_pair_at:
 205  * @segment: a #CpmlSegment
 206  * @pair:    the destination #CpmlPair
 207  * @pos:     the position value
 208  *
 209  * Gets the coordinates of the point lying on @segment at position
 210  * @pos. @pos is an homogeneous factor where %0 is the start point,
 211  * %1 the end point, %0.5 the mid point and so on.
 212  * The relation %0 < @pos < %1 should be satisfied, although some
 213  * cases accept value outside this range.
 214  *
 215  * <important>
 216  * <title>TODO</title>
 217  * <itemizedlist>
 218  * <listitem>The actual implementation returns only the start and end points,
 219  *           that is only when @pos is %0 or %1.</listitem>
 220  * </itemizedlist>
 221  * </important>
 222  **/
 223 void
 224 cpml_segment_pair_at(const CpmlSegment *segment, CpmlPair *pair, double pos)
 225 {
 226     CpmlPrimitive primitive;
 227
 228     cpml_primitive_from_segment(&primitive, (CpmlSegment *) segment);
 229
 230     /* Handle the common cases: start and end points */
 231     if (pos == 0)
 232         return cpml_primitive_pair_at(&primitive, pair, 0);
 233
 234     if (pos == 1) {
 235         while (cpml_primitive_next(&primitive))
 236             ;
 237         return cpml_primitive_pair_at(&primitive, pair, 1);
 238     }
 239 }
 240
 241 /**
 242  * cpml_segment_vector_at:
 243  * @segment: a #CpmlSegment
 244  * @vector:  the destination #CpmlVector
 245  * @pos:     the position value
 246  *
 247  * Gets the steepness of the point lying on @segment at position
 248  * @pos. @pos is an homogeneous factor where %0 is the start point,
 249  * %1 the end point, %0.5 the mid point and so on.
 250  * The relation %0 < @pos < %1 should be satisfied, although some
 251  * cases accept value outside this range.
 252  *
 253  * <important>
 254  * <title>TODO</title>
 255  * <itemizedlist>
 256  * <listitem>The actual implementation returns only the start and end
 257  *           steepness, that is only when @pos is %0 or %1.</listitem>
 258  * </itemizedlist>
 259  * </important>
 260  **/
 261 void
 262 cpml_segment_vector_at(const CpmlSegment *segment,
 263                        CpmlVector *vector, double pos)
 264 {
 265     CpmlPrimitive primitive;
 266
 267     cpml_primitive_from_segment(&primitive, (CpmlSegment *) segment);
 268
 269     /* Handle the common cases: start and end points */
 270     if (pos == 0) {
 271         cpml_primitive_vector_at(&primitive, vector, 0);
 272         return;
 273     }
 274
 275     if (pos == 1) {
 276         while (cpml_primitive_next(&primitive))
 277             ;
 278         cpml_primitive_vector_at(&primitive, vector, 1);
 279         return;
 280     }
 281 }
 282
 283
 284 /**
 285  * cpml_segment_to_cairo:
 286  * @segment: a #CpmlSegment
 287  * @cr: the destination cairo context
 288  *
 289  * Appends the path of @segment to @cr. The segment is "flattened",
 290  * that is %CAIRO_PATH_ARC_TO primitives are approximated by one
 291  * or more %CAIRO_PATH_CURVE_TO using cpml_arc_to_cairo(). Check
 292  * its documentation for further details.
 293  **/
 294 void
 295 cpml_segment_to_cairo(const CpmlSegment *segment, cairo_t *cr)
 296 {
 297     CpmlPrimitive primitive;
 298
 299     cpml_primitive_from_segment(&primitive, (CpmlSegment *) segment);
 300
 301     do {
 302         cpml_primitive_to_cairo(&primitive, cr);
 303     } while (cpml_primitive_next(&primitive));
 304 }
 305
 306 /**
 307  * cpml_segment_dump:
 308  * @segment: a #CpmlSegment
 309  *
 310  * Dumps the specified @segment to stdout. Useful for debugging purposes.
 311  **/
 312 void
 313 cpml_segment_dump(const CpmlSegment *segment)
 314 {
 315     CpmlPrimitive primitive;
 316     cairo_bool_t first_call = 1;
 317
 318     cpml_primitive_from_segment(&primitive, (CpmlSegment *) segment);
 319
 320     do {
 321         cpml_primitive_dump(&primitive, first_call);
 322         first_call = 0;
 323     } while (cpml_primitive_next(&primitive));
 324 }
 325
 326
 327 /**
 328  * cpml_segment_reverse:
 329  * @segment: a #CpmlSegment
 330  *
 331  * Reverses @segment in-place. The resulting rendering will be the same,
 332  * but with the primitives generated in reverse order.
 333  **/
 334 void
 335 cpml_segment_reverse(CpmlSegment *segment)
 336 {
 337     cairo_path_data_t *data, *dst_data;
 338     size_t data_size;
 339     double end_x, end_y;
 340     int n, num_points, n_point;
 341     const cairo_path_data_t *src_data;
 342
 343     data_size = sizeof(cairo_path_data_t) * segment->num_data;
 344     data = cpml_alloca(data_size);
 345     end_x = segment->data[1].point.x;
 346     end_y = segment->data[1].point.y;
 347
 348     for (n = 2; n < segment->num_data; ++n) {
 349         src_data = segment->data + n;
 350         num_points = src_data->header.length;
 351
 352         dst_data = data + segment->num_data - n - num_points + 2;
 353         dst_data->header.type = src_data->header.type;
 354         dst_data->header.length = num_points;
 355
 356         for (n_point = 1; n_point < num_points; ++n_point) {
 357             dst_data[num_points - n_point].point.x = end_x;
 358             dst_data[num_points - n_point].point.y = end_y;
 359             end_x = src_data[n_point].point.x;
 360             end_y = src_data[n_point].point.y;
 361         }
 362
 363         n += n_point - 1;
 364     }
 365
 366     data[0].header.type = CAIRO_PATH_MOVE_TO;
 367     data[0].header.length = 2;
 368     data[1].point.x = end_x;
 369     data[1].point.y = end_y;
 370     memcpy(segment->data, data, data_size);
 371 }
 372
 373 /**
 374  * cpml_segment_transform:
 375  * @segment: a #CpmlSegment
 376  * @matrix: the matrix to be applied
 377  *
 378  * Applies @matrix on all the points of @segment.
 379  **/
 380 void
 381 cpml_segment_transform(CpmlSegment *segment, const cairo_matrix_t *matrix)
 382 {
 383     cairo_path_data_t *data;
 384     int n, n_point, num_points;
 385
 386     data = segment->data;
 387
 388     for (n = 0; n < segment->num_data; n += num_points) {
 389         num_points = data->header.length;
 390         ++data;
 391         for (n_point = 1; n_point < num_points; ++n_point) {
 392             cairo_matrix_transform_point(matrix, &data->point.x, &data->point.y);
 393             ++data;
 394         }
 395     }
 396 }
 397
 398 /**
 399  * cpml_segment_intersection:
 400  * @segment:  the first #CpmlSegment
 401  * @segment2: the second #CpmlSegment
 402  * @dest:     the destination vector of #CpmlPair
 403  * @max:      maximum number of intersections to return
 404  *
 405  * Computes the intersections between @segment and @segment2 and
 406  * returns the found points in @dest. If the intersections are more
 407  * than @max, only the first @max pairs are stored in @dest.
 408  *
 409  * To get the job done, the primitives of @segment are sequentially
 410  * scanned for intersections with any primitive in @segment2. This
 411  * means @segment has a higher precedence over @segment2.
 412  *
 413  * Return value: the number of intersections found
 414  **/
 415 int
 416 cpml_segment_intersection(const CpmlSegment *segment,
 417                           const CpmlSegment *segment2,
 418                           CpmlPair *dest, int max)
 419 {
 420     CpmlPrimitive portion;
 421     int partial, total;
 422
 423     cpml_primitive_from_segment(&portion, (CpmlSegment *) segment);
 424     total = 0;
 425
 426     do {
 427         partial = cpml_primitive_intersection_with_segment(&portion,
 428                                                            segment2,
 429                                                            dest + total,
 430                                                            max - total);
 431         total += partial;
 432     } while (total < max && cpml_primitive_next(&portion));
 433
 434     return total;
 435 }
 436
 437 /**
 438  * cpml_segment_offset:
 439  * @segment: a #CpmlSegment
 440  * @offset: the offset distance
 441  *
 442  * Offsets a segment of the specified amount, that is builds a "parallel"
 443  * segment at the @offset distance from the original one and returns the
 444  * result by replacing the original @segment.
 445  *
 446  * <important>
 447  * <title>TODO</title>
 448  * <itemizedlist>
 449  * <listitem>Closed path are not yet managed: an elegant solution is not
 450  *           so obvious: use cpml_close_offset() when available.</listitem>
 451  * <listitem>Degenerated primitives, such as lines of length 0, are not
 452  *           managed properly.</listitem>
 453  * </itemizedlist>
 454  * </important>
 455  **/
 456 void
 457 cpml_segment_offset(CpmlSegment *segment, double offset)
 458 {
 459     CpmlPrimitive primitive;
 460     CpmlPrimitive last_primitive;
 461     cairo_path_data_t org, old_end;
 462     cairo_bool_t first_cycle;
 463
 464     cpml_primitive_from_segment(&primitive, segment);
 465     first_cycle = 1;
 466
 467     do {
 468         if (!first_cycle) {
 469             org = old_end;
 470             primitive.org = &org;
 471         }
 472
 473         old_end = *cpml_primitive_get_point(&primitive, -1);
 474         cpml_primitive_offset(&primitive, offset);
 475
 476         if (!first_cycle) {
 477             cpml_primitive_join(&last_primitive, &primitive);
 478             primitive.org = cpml_primitive_get_point(&last_primitive, -1);
 479         }
 480
 481         cpml_primitive_copy(&last_primitive, &primitive);
 482         first_cycle = 0;
 483     } while (cpml_primitive_next(&primitive));
 484 }
 485
 486 /**
 487  * normalize:
 488  * @segment: a #CpmlSegment
 489  *
 490  * Strips the leading %CAIRO_PATH_MOVE_TO primitives, updating
 491  * the CpmlSegment structure accordling. One, and only one,
 492  * %CAIRO_PATH_MOVE_TO primitive is left.
 493  *
 494  * Return value: 1 on success, 0 on no leading MOVE_TOs or on errors
 495  **/
 496 static cairo_bool_t
 497 normalize(CpmlSegment *segment)
 498 {
 499     if (!ensure_one_move_to(segment))
 500         return 0;
 501
 502     reshape(segment);
 503     return 1;
 504 }
 505
 506 /**
 507  * ensure_one_move_to:
 508  * @segment: a #CpmlSegment
 509  *
 510  * Strips the leading %CAIRO_PATH_MOVE_TO primitives, updating
 511  * the <structname>CpmlSegment</structname> structure accordling.
 512  * One, and only one, %CAIRO_PATH_MOVE_TO primitive is left.
 513  *
 514  * Return value: 1 on success, 0 on no leading MOVE_TOs or on empty path
 515  **/
 516 static cairo_bool_t
 517 ensure_one_move_to(CpmlSegment *segment)
 518 {
 519     cairo_path_data_t *new_data;
 520     int new_num_data, length;
 521
 522     new_data = segment->data;
 523
 524     /* Check for at least one move to */
 525     if (new_data->header.type != CAIRO_PATH_MOVE_TO)
 526         return 0;
 527
 528     new_num_data = segment->num_data;
 529     length = 0;
 530
 531     /* Strip the leading CAIRO_PATH_MOVE_TO, leaving only the last one */
 532     do {
 533         new_data += length;
 534         new_num_data -= length;
 535         length = new_data->header.length;
 536
 537         /* Check for end of cairo path data */
 538         if (length >= new_num_data)
 539             return 0;
 540     } while (new_data[length].header.type == CAIRO_PATH_MOVE_TO);
 541
 542     segment->data = new_data;
 543     segment->num_data = new_num_data;
 544
 545     return 1;
 546 }
 547
 548 /**
 549  * reshape:
 550  * @segment: a #CpmlSegment
 551  *
 552  * Looks for the segment termination and modify the
 553  * <structfield>num_data</structfield> field of @segment accordling.
 554  * @segment must have only one leading %CAIRO_PATH_MOVE_TO and
 555  * it is supposed to be non-empty, conditions yet imposed by the
 556  * ensure_one_move_to() function.
 557  **/
 558 static void
 559 reshape(CpmlSegment *segment)
 560 {
 561     cairo_path_data_t *data;
 562     int num_data, new_num_data, length;
 563
 564     /* Skip the leading move to */
 565     new_num_data = 2;
 566     data = segment->data + new_num_data;
 567
 568     /* Calculate the remaining data in the cairo path */
 569     num_data = segment->path->num_data -
 570                (segment->data - segment->path->data);
 571
 572     while (new_num_data < num_data) {
 573         /* A primitive is considered valid if it has implemented
 574          * its own type_get_npoints() */
 575         if (cpml_primitive_type_get_npoints(data->header.type) < 0)
 576             break;
 577
 578         length = data->header.length;
 579         data += length;
 580         new_num_data += length;
 581     }
 582
 583     segment->num_data = new_num_data;
 584 }