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: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_to_cairo:
 181  * @segment: a #CpmlSegment
 182  * @cr: the destination cairo context
 183  *
 184  * Appends the path of @segment to @cr. The segment is "flattened",
 185  * that is %CAIRO_PATH_ARC_TO primitives are approximated by one
 186  * or more %CAIRO_PATH_CURVE_TO using cpml_arc_to_cairo(). Check
 187  * its documentation for further details.
 188  **/
 189 void
 190 cpml_segment_to_cairo(const CpmlSegment *segment, cairo_t *cr)
 191 {
 192     CpmlPrimitive primitive;
 193
 194     cpml_primitive_from_segment(&primitive, (CpmlSegment *) segment);
 195
 196     do {
 197         cpml_primitive_to_cairo(&primitive, cr);
 198     } while (cpml_primitive_next(&primitive));
 199 }
 200
 201 /**
 202  * cpml_segment_dump:
 203  * @segment: a #CpmlSegment
 204  *
 205  * Dumps the specified @segment to stdout. Useful for debugging purposes.
 206  **/
 207 void
 208 cpml_segment_dump(const CpmlSegment *segment)
 209 {
 210     CpmlPrimitive primitive;
 211     cairo_bool_t first_call = 1;
 212
 213     cpml_primitive_from_segment(&primitive, (CpmlSegment *) segment);
 214
 215     do {
 216         cpml_primitive_dump(&primitive, first_call);
 217         first_call = 0;
 218     } while (cpml_primitive_next(&primitive));
 219 }
 220
 221
 222 /**
 223  * cpml_segment_reverse:
 224  * @segment: a #CpmlSegment
 225  *
 226  * Reverses @segment in-place. The resulting rendering will be the same,
 227  * but with the primitives generated in reverse order.
 228  **/
 229 void
 230 cpml_segment_reverse(CpmlSegment *segment)
 231 {
 232     cairo_path_data_t *data, *dst_data;
 233     size_t data_size;
 234     double end_x, end_y;
 235     int n, num_points, n_point;
 236     const cairo_path_data_t *src_data;
 237
 238     data_size = sizeof(cairo_path_data_t) * segment->num_data;
 239     data = cpml_alloca(data_size);
 240     end_x = segment->data[1].point.x;
 241     end_y = segment->data[1].point.y;
 242
 243     for (n = 2; n < segment->num_data; ++n) {
 244         src_data = segment->data + n;
 245         num_points = src_data->header.length;
 246
 247         dst_data = data + segment->num_data - n - num_points + 2;
 248         dst_data->header.type = src_data->header.type;
 249         dst_data->header.length = num_points;
 250
 251         for (n_point = 1; n_point < num_points; ++n_point) {
 252             dst_data[num_points - n_point].point.x = end_x;
 253             dst_data[num_points - n_point].point.y = end_y;
 254             end_x = src_data[n_point].point.x;
 255             end_y = src_data[n_point].point.y;
 256         }
 257
 258         n += n_point - 1;
 259     }
 260
 261     data[0].header.type = CAIRO_PATH_MOVE_TO;
 262     data[0].header.length = 2;
 263     data[1].point.x = end_x;
 264     data[1].point.y = end_y;
 265     memcpy(segment->data, data, data_size);
 266 }
 267
 268 /**
 269  * cpml_segment_transform:
 270  * @segment: a #CpmlSegment
 271  * @matrix: the matrix to be applied
 272  *
 273  * Applies @matrix on all the points of @segment.
 274  **/
 275 void
 276 cpml_segment_transform(CpmlSegment *segment, const cairo_matrix_t *matrix)
 277 {
 278     cairo_path_data_t *data;
 279     int n, n_point, num_points;
 280
 281     data = segment->data;
 282
 283     for (n = 0; n < segment->num_data; n += num_points) {
 284         num_points = data->header.length;
 285         ++data;
 286         for (n_point = 1; n_point < num_points; ++n_point) {
 287             cairo_matrix_transform_point(matrix, &data->point.x, &data->point.y);
 288             ++data;
 289         }
 290     }
 291 }
 292
 293 /**
 294  * cpml_segment_intersection:
 295  * @segment:  the first #CpmlSegment
 296  * @segment2: the second #CpmlSegment
 297  * @dest:     the destination vector of #CpmlPair
 298  * @max:      maximum number of intersections to return
 299  *
 300  * Computes the intersections between @segment and @segment2 and
 301  * returns the found points in @dest. If the intersections are more
 302  * than @max, only the first @max pairs are stored in @dest.
 303  *
 304  * To get the job done, the primitives of @segment are sequentially
 305  * scanned for intersections with any primitive in @segment2. This
 306  * means @segment has a higher precedence over @segment2.
 307  *
 308  * Return value: the number of intersections found
 309  **/
 310 int
 311 cpml_segment_intersection(const CpmlSegment *segment,
 312                           const CpmlSegment *segment2,
 313                           CpmlPair *dest, int max)
 314 {
 315     CpmlPrimitive portion;
 316     int partial, total;
 317
 318     cpml_primitive_from_segment(&portion, (CpmlSegment *) segment);
 319     total = 0;
 320
 321     do {
 322         partial = cpml_primitive_intersection_with_segment(&portion,
 323                                                            segment2,
 324                                                            dest + total,
 325                                                            max - total);
 326         total += partial;
 327     } while (total < max && cpml_primitive_next(&portion));
 328
 329     return total;
 330 }
 331
 332 /**
 333  * cpml_segment_offset:
 334  * @segment: a #CpmlSegment
 335  * @offset: the offset distance
 336  *
 337  * Offsets a segment of the specified amount, that is builds a "parallel"
 338  * segment at the @offset distance from the original one and returns the
 339  * result by replacing the original @segment.
 340  *
 341  * <important>
 342  * <title>TODO</title>
 343  * <itemizedlist>
 344  * <listitem>Closed path are not yet managed: an elegant solution is not
 345  *           so obvious: use cpml_close_offset() when available.</listitem>
 346  * <listitem>Degenerated primitives, such as lines of length 0, are not
 347  *           managed properly.</listitem>
 348  * </itemizedlist>
 349  * </important>
 350  **/
 351 void
 352 cpml_segment_offset(CpmlSegment *segment, double offset)
 353 {
 354     CpmlPrimitive primitive;
 355     CpmlPrimitive last_primitive;
 356     cairo_path_data_t org, old_end;
 357     cairo_bool_t first_cycle;
 358
 359     cpml_primitive_from_segment(&primitive, segment);
 360     first_cycle = 1;
 361
 362     do {
 363         if (!first_cycle) {
 364             org = old_end;
 365             primitive.org = &org;
 366         }
 367
 368         old_end = *cpml_primitive_get_point(&primitive, -1);
 369         cpml_primitive_offset(&primitive, offset);
 370
 371         if (!first_cycle) {
 372             cpml_primitive_join(&last_primitive, &primitive);
 373             primitive.org = cpml_primitive_get_point(&last_primitive, -1);
 374         }
 375
 376         cpml_primitive_copy(&last_primitive, &primitive);
 377         first_cycle = 0;
 378     } while (cpml_primitive_next(&primitive));
 379 }
 380
 381 /**
 382  * normalize:
 383  * @segment: a #CpmlSegment
 384  *
 385  * Strips the leading %CAIRO_PATH_MOVE_TO primitives, updating
 386  * the CpmlSegment structure accordling. One, and only one,
 387  * %CAIRO_PATH_MOVE_TO primitive is left.
 388  *
 389  * Return value: 1 on success, 0 on no leading MOVE_TOs or on errors
 390  **/
 391 static cairo_bool_t
 392 normalize(CpmlSegment *segment)
 393 {
 394     if (!ensure_one_move_to(segment))
 395         return 0;
 396
 397     reshape(segment);
 398     return 1;
 399 }
 400
 401 /**
 402  * ensure_one_move_to:
 403  * @segment: a #CpmlSegment
 404  *
 405  * Strips the leading %CAIRO_PATH_MOVE_TO primitives, updating
 406  * the <structname>CpmlSegment</structname> structure accordling.
 407  * One, and only one, %CAIRO_PATH_MOVE_TO primitive is left.
 408  *
 409  * Return value: 1 on success, 0 on no leading MOVE_TOs or on empty path
 410  **/
 411 static cairo_bool_t
 412 ensure_one_move_to(CpmlSegment *segment)
 413 {
 414     cairo_path_data_t *new_data;
 415     int new_num_data, length;
 416
 417     new_data = segment->data;
 418
 419     /* Check for at least one move to */
 420     if (new_data->header.type != CAIRO_PATH_MOVE_TO)
 421         return 0;
 422
 423     new_num_data = segment->num_data;
 424     length = 0;
 425
 426     /* Strip the leading CAIRO_PATH_MOVE_TO, leaving only the last one */
 427     do {
 428         new_data += length;
 429         new_num_data -= length;
 430         length = new_data->header.length;
 431
 432         /* Check for end of cairo path data */
 433         if (length >= new_num_data)
 434             return 0;
 435     } while (new_data[length].header.type == CAIRO_PATH_MOVE_TO);
 436
 437     segment->data = new_data;
 438     segment->num_data = new_num_data;
 439
 440     return 1;
 441 }
 442
 443 /**
 444  * reshape:
 445  * @segment: a #CpmlSegment
 446  *
 447  * Looks for the segment termination and modify the
 448  * <structfield>num_data</structfield> field of @segment accordling.
 449  * @segment must have only one leading %CAIRO_PATH_MOVE_TO and
 450  * it is supposed to be non-empty, conditions yet imposed by the
 451  * ensure_one_move_to() function.
 452  **/
 453 static void
 454 reshape(CpmlSegment *segment)
 455 {
 456     cairo_path_data_t *data;
 457     int num_data, new_num_data, length;
 458
 459     /* Skip the leading move to */
 460     new_num_data = 2;
 461     data = segment->data + new_num_data;
 462
 463     /* Calculate the remaining data in the cairo path */
 464     num_data = segment->path->num_data -
 465                (segment->data - segment->path->data);
 466
 467     while (new_num_data < num_data) {
 468         /* A primitive is considered valid if it has implemented
 469          * its own type_get_npoints() */
 470         if (cpml_primitive_type_get_npoints(data->header.type) < 0)
 471             break;
 472
 473         length = data->header.length;
 474         data += length;
 475         new_num_data += length;
 476     }
 477
 478     segment->num_data = new_num_data;
 479 }