cpml/cpml-primitive.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  * SECTION:primitive
  22  * @title: CpmlPrimitive
  23  * @short_description: Basic component of segments
  24  *
  25  * A primitive is an atomic geometric element found inside #CpmlSegment.
  26  * The available primitives are defined in the #cairo_path_data_type_t
  27  * enum, excluding %CAIRO_PATH_MOVE_TO, as it is not considered a valid
  28  * primitive and it is managed in different way (the moveto primitives
  29  * are used to set the origin of the first primitive in a segment).
  30  **/
  31
  32 /**
  33  * CpmlPrimitive:
  34  * @segment: the source #CpmlSegment
  35  * @org: a pointer to the first point of the primitive
  36  * @data: the array of the path data, prepended by the header
  37  *
  38  * As for #CpmlSegment, also the primitive is unobtrusive. This
  39  * means CpmlPrimitive does not include any coordinates but instead
  40  * keeps pointers to the original segment (and, by transition, to
  41  * the underlying #cairo_path_t struct).
  42  **/
  43
  44 #include "cpml-primitive.h"
  45 #include "cpml-line.h"
  46 #include "cpml-arc.h"
  47 #include "cpml-curve.h"
  48 #include "cpml-close.h"
  49
  50 #include <stdlib.h>
  51 #include <string.h>
  52 #include <stdio.h>
  53
  54 static void     dump_cairo_point        (const cairo_path_data_t *path_data);
  55
  56
  57 /**
  58  * cpml_primitive_copy:
  59  * @primitive: the destination #CpmlPrimitive
  60  * @src: the source #CpmlPrimitive
  61  *
  62  * Copies @src in @primitive.
  63  *
  64  * Return value: @primitive
  65  **/
  66 CpmlPrimitive *
  67 cpml_primitive_copy(CpmlPrimitive *primitive, const CpmlPrimitive *src)
  68 {
  69     return memcpy(primitive, src, sizeof(CpmlPrimitive));
  70 }
  71
  72 /**
  73  * cpml_primitive_from_segment:
  74  * @primitive: the destination #CpmlPrimitive struct
  75  * @segment: the source segment
  76  *
  77  * Initializes @primitive to the first primitive of @segment.
  78  *
  79  * Return value: @primitive
  80  **/
  81 CpmlPrimitive *
  82 cpml_primitive_from_segment(CpmlPrimitive *primitive, CpmlSegment *segment)
  83 {
  84     primitive->segment = segment;
  85
  86     /* The first element of a CpmlSegment is always a CAIRO_PATH_MOVE_TO,
  87      * as ensured by cpml_segment_from_cairo() and by the browsing APIs,
  88      * so the origin is in the second data item */
  89     primitive->org = &segment->data[1];
  90
  91     /* Also, the segment APIs ensure that @segment is prepended by
  92      * only one CAIRO_PATH_MOVE_TO */
  93     primitive->data = segment->data + 2;
  94
  95     return primitive;
  96 }
  97
  98 /**
  99  * cpml_primitive_reset:
 100  * @primitive: a #CpmlPrimitive
 101  *
 102  * Resets @primitive so it refers to the first primitive of the
 103  * source segment.
 104  **/
 105 void
 106 cpml_primitive_reset(CpmlPrimitive *primitive)
 107 {
 108     primitive->org = &primitive->segment->data[1];
 109     primitive->data = primitive->segment->data + 2;
 110 }
 111
 112 /**
 113  * cpml_primitive_next:
 114  * @primitive: a #CpmlPrimitive
 115  *
 116  *
 117  * Changes @primitive so it refers to the next primitive on the
 118  * source segment. If there are no more primitives, @primitive is
 119  * not changed and 0 is returned.
 120  *
 121  * Return value: 1 on success, 0 if no next primitive found or errors
 122  **/
 123 cairo_bool_t
 124 cpml_primitive_next(CpmlPrimitive *primitive)
 125 {
 126     cairo_path_data_t *new_data;
 127
 128     new_data = primitive->data + primitive->data->header.length;
 129     if (new_data - primitive->segment->data >= primitive->segment->num_data)
 130         return 0;
 131
 132     primitive->org = cpml_primitive_get_point(primitive, -1);
 133     primitive->data = new_data;
 134
 135     return 1;
 136 }
 137
 138 /**
 139  * cpml_primitive_get_npoints:
 140  * @primitive: a #CpmlPrimitive
 141  *
 142  * Gets the number of points required to identify @primitive.
 143  * It is similar to cpml_primitive_type_get_npoints() but using
 144  * a @primitive instance instead of a type.
 145  *
 146  * Return value: the number of points or -1 on errors
 147  **/
 148 int
 149 cpml_primitive_get_npoints(const CpmlPrimitive *primitive)
 150 {
 151     return cpml_primitive_type_get_npoints(primitive->data->header.type);
 152 }
 153
 154 /**
 155  * cpml_primitive_get_point:
 156  * @primitive: a #CpmlPrimitive
 157  * @npoint: the index of the point to retrieve
 158  *
 159  * Gets the specified @npoint from @primitive. The index starts
 160  * at 0: if @npoint is 0, the start point (the origin) is
 161  * returned, 1 for the second point and so on. If @npoint is
 162  * negative, it is considered as a negative index from the end,
 163  * so that -1 is the end point, -2 the point before the end point
 164  * and so on.
 165  *
 166  * %CAIRO_PATH_CLOSE_PATH is managed in a special way: if @npoint
 167  * is -1 or 1 and @primitive is a close-path, this function cycles
 168  * the source #CpmlSegment and returns the first point. This is
 169  * needed because requesting the end point (or the second point)
 170  * of a close path is a valid operation and must returns the start
 171  * of the segment.
 172  *
 173  * Return value: a pointer to the requested point (in cairo format)
 174  *               or %NULL if the point is outside the valid range
 175  **/
 176 cairo_path_data_t *
 177 cpml_primitive_get_point(const CpmlPrimitive *primitive, int npoint)
 178 {
 179     int npoints;
 180
 181     /* For a start point request, simply return the origin
 182      * without further checking */
 183     if (npoint == 0)
 184         return primitive->org;
 185
 186     /* The CAIRO_PATH_CLOSE_PATH special case */
 187     if (primitive->data->header.type == CAIRO_PATH_CLOSE_PATH &&
 188         (npoint == 1 || npoint == -1))
 189         return &primitive->segment->data[1];
 190
 191     npoints = cpml_primitive_get_npoints(primitive);
 192     if (npoints < 0)
 193         return NULL;
 194
 195     /* If npoint is negative, consider it as a negative index from the end */
 196     if (npoint < 0)
 197         npoint = npoints + npoint;
 198
 199     /* Out of range condition */
 200     if (npoint < 0 || npoint >= npoints)
 201         return NULL;
 202
 203     return npoint == 0 ? primitive->org : &primitive->data[npoint];
 204 }
 205
 206 /**
 207  * cpml_primitive_to_cairo:
 208  * @primitive: a #CpmlPrimitive
 209  * @cr: the destination cairo context
 210  *
 211  * Renders a single @primitive to the @cr cairo context.
 212  * As a special case, if the primitive is a #CAIRO_PATH_CLOSE_PATH,
 213  * an equivalent line is rendered, because a close path left alone
 214  * is not renderable.
 215  *
 216  * Also a #CAIRO_PATH_ARC_TO primitive is treated specially, as it
 217  * is not natively supported by cairo and has its own rendering API.
 218  **/
 219 void
 220 cpml_primitive_to_cairo(const CpmlPrimitive *primitive, cairo_t *cr)
 221 {
 222     cairo_path_t path;
 223     cairo_path_data_t *path_data;
 224
 225     cairo_move_to(cr, primitive->org->point.x, primitive->org->point.y);
 226
 227     if (primitive->data->header.type == CAIRO_PATH_CLOSE_PATH) {
 228         path_data = cpml_primitive_get_point(primitive, -1);
 229         cairo_line_to(cr, path_data->point.x, path_data->point.y);
 230     } else if (primitive->data->header.type == CAIRO_PATH_ARC_TO) {
 231         cpml_arc_to_cairo(primitive, cr);
 232     } else {
 233         path.status = CAIRO_STATUS_SUCCESS;
 234         path.data = primitive->data;
 235         path.num_data = primitive->data->header.length;
 236         cairo_append_path(cr, &path);
 237     }
 238 }
 239
 240 /**
 241  * cpml_primitive_dump:
 242  * @primitive: a #CpmlPrimitive
 243  * @org_also:  whether to output also the origin coordinates
 244  *
 245  * Dumps info on the specified @primitive to stdout: useful for
 246  * debugging purposes. If @org_also is 1, a %CAIRO_PATH_MOVE_TO
 247  * to the origin is prepended to the data otherwise the
 248  * <structfield>org</structfield> field is not used.
 249  **/
 250 void
 251 cpml_primitive_dump(const CpmlPrimitive *primitive, cairo_bool_t org_also)
 252 {
 253     const cairo_path_data_t *data;
 254     int type, n, npoints;
 255
 256     data = primitive->data;
 257     type = data->header.type;
 258     npoints = cpml_primitive_get_npoints(primitive);
 259     if (npoints < 0) {
 260         printf("Unhandled primitive type (%d)\n", type);
 261         return;
 262     }
 263
 264     /* Dump the origin movement, if requested */
 265     if (org_also) {
 266         printf("Move to ");
 267         dump_cairo_point(primitive->org);
 268         printf("\n");
 269     }
 270
 271     switch (type) {
 272
 273     case CAIRO_PATH_LINE_TO:
 274         printf("Line to ");
 275         break;
 276
 277     case CAIRO_PATH_ARC_TO:
 278         printf("Arc to ");
 279         break;
 280
 281     case CAIRO_PATH_CURVE_TO:
 282         printf("Curve to ");
 283         break;
 284
 285     case CAIRO_PATH_CLOSE_PATH:
 286         printf("Path close");
 287         break;
 288
 289     default:
 290         printf("Unknown primitive (type = %d)", type);
 291         break;
 292     }
 293
 294     for (n = 1; n < npoints; ++n)
 295         dump_cairo_point(cpml_primitive_get_point(primitive, n));
 296
 297     printf("\n");
 298 }
 299
 300 /**
 301  * cpml_primitive_intersection_with_segment:
 302  * @primitive: a #CpmlPrimitive
 303  * @segment:   a #CpmlSegment
 304  * @dest:      the destination vector of #CpmlPair
 305  * @max:       maximum number of intersections to return
 306  *
 307  * Computes the intersections between @segment and @primitive by
 308  * sequentially scanning the primitives in @segment and looking
 309  * for intersections with @primitive.
 310  * If the intersections are more than @max, only the first @max pairs
 311  * are stored in @dest.
 312  *
 313  * Return value: the number of intersections found
 314  **/
 315 int
 316 cpml_primitive_intersection_with_segment(const CpmlPrimitive *primitive,
 317                                          const CpmlSegment *segment,
 318                                          CpmlPair *dest, int max)
 319 {
 320     CpmlPrimitive portion;
 321     int partial, total;
 322     CpmlPair tmp_pairs[4];
 323
 324     cpml_primitive_from_segment(&portion, (CpmlSegment *) segment);
 325     total = 0;
 326
 327     do {
 328         partial = cpml_primitive_intersection(&portion, primitive, tmp_pairs);
 329         if (total + partial > max)
 330             partial = max - total;
 331
 332         if (partial > 0) {
 333             memcpy(dest + total, tmp_pairs, partial * sizeof(CpmlPair));
 334             total += partial;
 335         }
 336     } while (total < max && cpml_primitive_next(&portion));
 337
 338     return total;
 339 }
 340
 341
 342 /**
 343  * cpml_primitive_type_get_npoints:
 344  * @type: a primitive type
 345  *
 346  * Gets the number of points required to identify the @type primitive.
 347  *
 348  * <note><para>
 349  * This function is primitive dependent, that is every primitive has
 350  * its own implementation.
 351  * </para></note>
 352  *
 353  * Return value: the number of points or -1 on errors
 354  **/
 355 int
 356 cpml_primitive_type_get_npoints(cairo_path_data_type_t type)
 357 {
 358     switch (type) {
 359
 360     case CAIRO_PATH_LINE_TO:
 361         return cpml_line_type_get_npoints();
 362
 363     case CAIRO_PATH_ARC_TO:
 364         return cpml_arc_type_get_npoints();
 365
 366     case CAIRO_PATH_CURVE_TO:
 367         return cpml_curve_type_get_npoints();
 368
 369     case CAIRO_PATH_CLOSE_PATH:
 370         return cpml_close_type_get_npoints();
 371
 372     default:
 373         break;
 374     }
 375
 376     return -1;
 377 }
 378
 379 /**
 380  * cpml_primitive_pair_at:
 381  * @primitive: a #CpmlPrimitive
 382  * @pair:      the destination #CpmlPair
 383  * @pos:       the position value
 384  *
 385  * Abstracts the pair_at() family functions by providing a common
 386  * way to access the underlying primitive-specific implementation.
 387  *
 388  * It gets the coordinates of the point lying on @primitive
 389  * at position @pos. @pos is an homogeneous factor where 0 is the
 390  * start point, 1 the end point, 0.5 the mid point and so on.
 391  * The relation 0 < @pos < 1 should be satisfied, although some
 392  * primitives accept value outside this range.
 393  *
 394  * <note><para>
 395  * This function is primitive dependent, that is every primitive has
 396  * its own implementation.
 397  * </para></note>
 398  **/
 399 void
 400 cpml_primitive_pair_at(const CpmlPrimitive *primitive,
 401                        CpmlPair *pair, double pos)
 402 {
 403     switch (primitive->data->header.type) {
 404
 405     case CAIRO_PATH_LINE_TO:
 406         cpml_line_pair_at(primitive, pair, pos);
 407         break;
 408
 409     case CAIRO_PATH_ARC_TO:
 410         cpml_arc_pair_at(primitive, pair, pos);
 411         break;
 412
 413     case CAIRO_PATH_CURVE_TO:
 414         cpml_curve_pair_at(primitive, pair, pos);
 415         break;
 416
 417     case CAIRO_PATH_CLOSE_PATH:
 418         cpml_close_pair_at(primitive, pair, pos);
 419         break;
 420
 421     default:
 422         break;
 423     }
 424 }
 425
 426 /**
 427  * cpml_primitive_vector_at:
 428  * @primitive: a #CpmlPrimitive
 429  * @vector:    the destination #CpmlVector
 430  * @pos:       the position value
 431  *
 432  * Abstracts the vector_at() family functions by providing a common
 433  * way to access the underlying primitive-specific implementation.
 434  *
 435  * It gets the steepness of the point at position @pos on @primitive.
 436  * @pos is an homogeneous factor where 0 is the start point, 1 the
 437  * end point, 0.5 the mid point and so on.
 438  * The relation 0 < @pos < 1 should be satisfied, although some
 439  * primitives accept value outside this range.
 440  *
 441  * <note><para>
 442  * This function is primitive dependent, that is every primitive has
 443  * its own implementation.
 444  * </para></note>
 445  **/
 446 void
 447 cpml_primitive_vector_at(const CpmlPrimitive *primitive,
 448                          CpmlVector *vector, double pos)
 449 {
 450     switch (primitive->data->header.type) {
 451
 452     case CAIRO_PATH_LINE_TO:
 453         cpml_line_vector_at(primitive, vector, pos);
 454         break;
 455
 456     case CAIRO_PATH_ARC_TO:
 457         cpml_arc_vector_at(primitive, vector, pos);
 458         break;
 459
 460     case CAIRO_PATH_CURVE_TO:
 461         cpml_curve_vector_at(primitive, vector, pos);
 462         break;
 463
 464     case CAIRO_PATH_CLOSE_PATH:
 465         cpml_close_vector_at(primitive, vector, pos);
 466         break;
 467
 468     default:
 469         break;
 470     }
 471 }
 472
 473 /**
 474  * cpml_primitive_join:
 475  * @primitive: the first #CpmlPrimitive
 476  * @primitive2: the second #CpmlPrimitive
 477  *
 478  * Joins two primitive modifying the end point of @primitive and the
 479  * start point of @primitive2 so that the resulting points will overlap.
 480  *
 481  * <important>
 482  * <title>TODO</title>
 483  * <itemizedlist>
 484  * <listitem>Actually, the join is done by extending the end vector
 485  *           of @primitive and the start vector of @primitive2 and
 486  *           interpolating the intersection: this means no primitive
 487  *           dependent code is needed. Anyway, it is likely to change
 488  *           in the future because this approach is quite naive when
 489  *           curves are involved.</listitem>
 490  * </itemizedlist>
 491  * </important>
 492  *
 493  * Return value: 1 on success, 0 if the end vector of @primitive
 494  *               and the start vector of @primitive2 are parallel
 495  **/
 496 cairo_bool_t
 497 cpml_primitive_join(CpmlPrimitive *primitive, CpmlPrimitive *primitive2)
 498 {
 499     cairo_path_data_t *end1, *start2;
 500     CpmlPrimitive line1, line2;
 501     cairo_path_data_t data1[2], data2[2];
 502     CpmlPair joint;
 503
 504     end1 = cpml_primitive_get_point(primitive, -1);
 505     start2 = cpml_primitive_get_point(primitive2, 0);
 506
 507     /* Check if the primitives are yet connected */
 508     if (end1->point.x == start2->point.x && end1->point.y == start2->point.y)
 509         return 1;
 510
 511     line1.org = cpml_primitive_get_point(primitive, -2);
 512     line1.data = data1;
 513     data1[0].header.type = CAIRO_PATH_LINE_TO;
 514     data1[1] = *end1;
 515
 516     line2.org = start2;
 517     line2.data = data2;
 518     data2[0].header.type = CAIRO_PATH_LINE_TO;
 519     data2[1] = *cpml_primitive_get_point(primitive2, 1);
 520
 521     if (!cpml_line_intersection(&line1, &line2, &joint))
 522         return 0;
 523
 524     cpml_pair_to_cairo(&joint, end1);
 525     cpml_pair_to_cairo(&joint, start2);
 526
 527     return 1;
 528 }
 529
 530 /**
 531  * cpml_primitive_intersection:
 532  * @primitive:  the first #CpmlPrimitive
 533  * @primitive2: the second #CpmlPrimitive
 534  * @dest:       the destination #CpmlPair (or a vector of #CpmlPair)
 535  *
 536  * Finds the intersection points between the given primitives and
 537  * returns the result in @dest. The size of @dest is dependent
 538  * from the type of the most complex primitive involved in the
 539  * operation. If there are curves involved, @dest MUST be an array
 540  * of at least 4 #CpmlPair. If an arc is the most complex primitive
 541  * involved, @dest MUST be sized to 2 #CpmlPair. In the simplest
 542  * case, that is intersection between two lines, only 1 #CpmlPair
 543  * is required.
 544  *
 545  * If the primitive types are not known in advance, simply suppose
 546  * the worst case and leave room for 4 #CpmlPair in @dest.
 547  *
 548  * <note><para>
 549  * This function is primitive dependent: every new primitive must
 550  * expose API to get intersections with any other primitive type
 551  * (excluding %CAIRO_PATH_CLOSE_PATH, as it is converted to a line
 552  * primitive).</para>
 553  * <para>The convention used by CPML is that a primitive should
 554  * expose only APIs dealing with lower complexity primitives.
 555  * This is required to avoid double functions: you will have
 556  * only a cpml_curve_intersection_with_line() function not a
 557  * cpml_line_intersection_with_curve(), as the latter is
 558  * easily reproduced by calling the former with @primitive2
 559  * and @primitive switched.
 560  * </para></note>
 561  *
 562  * Return value: the number of intersection points found
 563  **/
 564 int
 565 cpml_primitive_intersection(const CpmlPrimitive *primitive,
 566                             const CpmlPrimitive *primitive2,
 567                             CpmlPair *dest)
 568 {
 569     cairo_path_data_type_t type1, type2;
 570
 571     type1 = primitive->data->header.type;
 572     type2 = primitive->data->header.type;
 573
 574     /* Close path primitives are treated as line-to */
 575     if (type1 == CAIRO_PATH_CLOSE_PATH)
 576         type1 = CAIRO_PATH_LINE_TO;
 577     if (type2 == CAIRO_PATH_CLOSE_PATH)
 578         type2 = CAIRO_PATH_LINE_TO;
 579
 580     /* Order the two primitives in ascending complexity, to facilitate
 581      * the dispatcher logic */
 582     if (cpml_primitive_type_get_npoints(type1) > cpml_primitive_type_get_npoints(type2)) {
 583         const CpmlPrimitive *tmp_primitive;
 584         cairo_path_data_type_t tmp_type;
 585
 586         tmp_type = type1;
 587         tmp_primitive = primitive;
 588
 589         type1 = type2;
 590         primitive = primitive2;
 591
 592         type2 = tmp_type;
 593         primitive2 = tmp_primitive;
 594     }
 595
 596     /* Dispatcher: probably there's a smarter way to do this */
 597     switch (type1) {
 598
 599     case CAIRO_PATH_LINE_TO:
 600         if (type2 == CAIRO_PATH_LINE_TO)
 601             return cpml_line_intersection(primitive2, primitive, dest);
 602         else if (type2 == CAIRO_PATH_ARC_TO)
 603             return cpml_arc_intersection_with_line(primitive2, primitive, dest);
 604         else if (type2 == CAIRO_PATH_CURVE_TO)
 605             return cpml_curve_intersection_with_line(primitive2, primitive, dest);
 606         break;
 607
 608     case CAIRO_PATH_ARC_TO:
 609         if (type2 == CAIRO_PATH_ARC_TO)
 610             return cpml_arc_intersection(primitive2, primitive, dest);
 611         else if (type2 == CAIRO_PATH_CURVE_TO)
 612             return cpml_curve_intersection_with_arc(primitive2, primitive, dest);
 613         break;
 614
 615     case CAIRO_PATH_CURVE_TO:
 616         if (type2 == CAIRO_PATH_CURVE_TO)
 617             return cpml_curve_intersection(primitive2, primitive, dest);
 618         break;
 619
 620     default:
 621         break;
 622     }
 623
 624     /* Primitive combination not found */
 625     return 0;
 626 }
 627
 628 /**
 629  * cpml_primitive_offset:
 630  * @primitive: a #CpmlPrimitive
 631  * @offset: distance for the computed offset primitive
 632  *
 633  * Given a primitive, computes the same (or approximated) parallel
 634  * primitive distant @offset from the original one and returns
 635  * the result by changing @primitive.
 636  *
 637  * <note><para>
 638  * This function is primitive dependent, that is every primitive has
 639  * its own implementation.
 640  * </para></note>
 641  **/
 642 void
 643 cpml_primitive_offset(CpmlPrimitive *primitive, double offset)
 644 {
 645     switch (primitive->data->header.type) {
 646
 647     case CAIRO_PATH_LINE_TO:
 648         cpml_line_offset(primitive, offset);
 649         break;
 650
 651     case CAIRO_PATH_ARC_TO:
 652         cpml_arc_offset(primitive, offset);
 653         break;
 654
 655     case CAIRO_PATH_CURVE_TO:
 656         cpml_curve_offset(primitive, offset);
 657         break;
 658
 659     case CAIRO_PATH_CLOSE_PATH:
 660         cpml_close_offset(primitive, offset);
 661         break;
 662
 663     default:
 664         break;
 665     }
 666 }
 667
 668 static void
 669 dump_cairo_point(const cairo_path_data_t *path_data)
 670 {
 671     printf("(%g %g) ", path_data->point.x, path_data->point.y);
 672 }