src/cpml/cpml-primitive.c

   1 /* CPML - Cairo Path Manipulation Library
   2  * Copyright (C) 2008,2009,2010  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-primitive
  23  * @Section_Id:CpmlPrimitive
  24  * @title: CpmlPrimitive
  25  * @short_description: Basic component of segments
  26  *
  27  * A primitive is an atomic geometric element found inside #CpmlSegment.
  28  * The available primitives are the same defined by #cairo_path_data_type_t
  29  * with the additional #CPML_ARC type (check #CpmlPrimitiveType
  30  * for further information) and without #CPML_MOVE as it is not
  31  * considered a primitive and it is managed in different way: the move-to
  32  * primitives are only used to define the origin of a segment.
  33  **/
  34
  35 /**
  36  * CpmlPrimitiveType:
  37  *
  38  * This is another name for #cairo_path_data_type_t type. Although
  39  * phisically they are the same struct, #CpmlPrimitiveType conceptually
  40  * embodies an important difference: it can be used to specify the
  41  * special #CPML_ARC primitive. This is not a native cairo
  42  * primitive and having two different types is a good way to make clear
  43  * when a function expect or not embedded arc-to primitives.
  44  **/
  45
  46 /**
  47  * CpmlPrimitive:
  48  * @segment: the source #CpmlSegment
  49  * @org: a pointer to the first point of the primitive
  50  * @data: the array of the path data, prepended by the header
  51  *
  52  * As for #CpmlSegment, also the primitive is unobtrusive. This
  53  * means CpmlPrimitive does not include any coordinates but instead
  54  * keeps pointers to the original segment (and, by transition, to
  55  * the underlying #CpmlPath struct).
  56  **/
  57
  58 /**
  59  * CPML_MOVE:
  60  *
  61  * An operation that denotes a current point movement internally used to
  62  * keep track of the starting point of a primitive.
  63  * It is equivalent to the %CAIRO_PATH_MOVE_TO cairo constant.
  64  **/
  65
  66
  67 #include "cpml-internal.h"
  68 #include "cpml-extents.h"
  69 #include "cpml-segment.h"
  70 #include "cpml-primitive.h"
  71 #include "cpml-primitive-private.h"
  72 #include "cpml-line.h"
  73 #include "cpml-arc.h"
  74 #include "cpml-curve.h"
  75 #include "cpml-close.h"
  76 #include <string.h>
  77 #include <stdio.h>
  78
  79
  80 static const _CpmlPrimitiveClass *
  81                 get_class_from_type     (CpmlPrimitiveType        type);
  82 static const _CpmlPrimitiveClass *
  83                 get_class               (const CpmlPrimitive     *primitive);
  84 static void     dump_cairo_point        (const cairo_path_data_t *path_data);
  85
  86
  87 /**
  88  * cpml_primitive_type_get_n_points:
  89  * @type: a primitive type
  90  *
  91  * Gets the number of points required to identify the @type primitive.
  92  *
  93  * Returns: the number of points or %0 on errors
  94  **/
  95 size_t
  96 cpml_primitive_type_get_n_points(CpmlPrimitiveType type)
  97 {
  98     const _CpmlPrimitiveClass *class_data = get_class_from_type(type);
  99
 100     if (class_data == NULL)
 101         return 0;
 102
 103     return class_data->n_points;
 104 }
 105
 106 /**
 107  * cpml_primitive_from_segment:
 108  * @primitive: the destination #CpmlPrimitive struct
 109  * @segment: the source segment
 110  *
 111  * Initializes @primitive to the first primitive of @segment.
 112  **/
 113 void
 114 cpml_primitive_from_segment(CpmlPrimitive *primitive, CpmlSegment *segment)
 115 {
 116     primitive->segment = segment;
 117
 118     /* The first element of a CpmlSegment is always a CPML_MOVE,
 119      * as ensured by cpml_segment_from_cairo() and by the browsing APIs,
 120      * so the origin is in the second data item */
 121     primitive->org = segment->data + 1;
 122
 123     /* Also, the segment APIs ensure that @segment is prepended by
 124      * only one CPML_MOVE */
 125     primitive->data = segment->data + segment->data->header.length;
 126 }
 127
 128 /**
 129  * cpml_primitive_copy:
 130  * @primitive: the destination #CpmlPrimitive
 131  * @src: the source #CpmlPrimitive
 132  *
 133  * Copies @src in @primitive. This is a shallow copy: the internal fields
 134  * of @primitive refer to the same memory as the original @src primitive.
 135  **/
 136 void
 137 cpml_primitive_copy(CpmlPrimitive *primitive, const CpmlPrimitive *src)
 138 {
 139     memcpy(primitive, src, sizeof(CpmlPrimitive));
 140 }
 141
 142 /**
 143  * cpml_primitive_reset:
 144  * @primitive: a #CpmlPrimitive
 145  *
 146  * Resets @primitive so it refers to the first primitive of the
 147  * source segment.
 148  **/
 149 void
 150 cpml_primitive_reset(CpmlPrimitive *primitive)
 151 {
 152     cpml_primitive_from_segment(primitive, primitive->segment);
 153 }
 154
 155 /**
 156  * cpml_primitive_next:
 157  * @primitive: a #CpmlPrimitive
 158  *
 159  *
 160  * Changes @primitive so it refers to the next primitive on the
 161  * source segment. If there are no more primitives, @primitive is
 162  * not changed and 0 is returned.
 163  *
 164  * Returns: 1 on success, 0 if no next primitive found or errors
 165  **/
 166 cairo_bool_t
 167 cpml_primitive_next(CpmlPrimitive *primitive)
 168 {
 169     cairo_path_data_t *new_data;
 170     const cairo_path_data_t *end_data;
 171
 172     new_data = primitive->data + primitive->data->header.length;
 173     end_data = primitive->segment->data + primitive->segment->num_data;
 174
 175     if (new_data >= end_data)
 176         return 0;
 177
 178     primitive->org = cpml_primitive_get_point(primitive, -1);
 179     primitive->data = new_data;
 180
 181     return 1;
 182 }
 183
 184 /**
 185  * cpml_primitive_get_n_points:
 186  * @primitive: a #CpmlPrimitive
 187  *
 188  * Gets the number of points required to identify @primitive.
 189  * It is similar to cpml_primitive_type_get_n_points() but using
 190  * a @primitive instance instead of a type.
 191  *
 192  * Returns: the number of points or %0 on errors
 193  **/
 194 size_t
 195 cpml_primitive_get_n_points(const CpmlPrimitive *primitive)
 196 {
 197     return cpml_primitive_type_get_n_points(primitive->data->header.type);
 198 }
 199
 200 /**
 201  * cpml_primitive_get_point:
 202  * @primitive: a #CpmlPrimitive
 203  * @n_point: the index of the point to retrieve
 204  *
 205  * Gets the specified @n_point from @primitive. The index starts
 206  * at 0: if @n_point is 0, the start point (the origin) is
 207  * returned, 1 for the second point and so on. If @n_point is
 208  * negative, it is considered as a negative index from the end,
 209  * so that -1 is the end point, -2 the point before the end point
 210  * and so on.
 211  *
 212  * #CPML_CLOSE is managed in a special way: if @n_point
 213  * is -1 or 1 and @primitive is a close-path, this function cycles
 214  * the source #CpmlSegment and returns the first point. This is
 215  * needed because requesting the end point (or the second point)
 216  * of a close path is a valid operation and must returns the start
 217  * of the segment.
 218  *
 219  * Returns: a pointer to the requested point (in cairo format)
 220  *          or %NULL if the point is outside the valid range
 221  **/
 222 cairo_path_data_t *
 223 cpml_primitive_get_point(const CpmlPrimitive *primitive, int n_point)
 224 {
 225     size_t n_points;
 226
 227     /* For a start point request, simply return the origin
 228      * without further checking */
 229     if (n_point == 0)
 230         return primitive->org;
 231
 232     /* The CPML_CLOSE special case */
 233     if (primitive->data->header.type == CPML_CLOSE &&
 234         (n_point == 1 || n_point == -1))
 235         return &primitive->segment->data[1];
 236
 237     n_points = cpml_primitive_get_n_points(primitive);
 238     if (n_points == 0)
 239         return NULL;
 240
 241     /* If n_point is negative, consider it as a negative index from the end */
 242     if (n_point < 0)
 243         n_point = n_points + n_point;
 244
 245     /* Out of range condition */
 246     if (n_point < 0 || n_point >= n_points)
 247         return NULL;
 248
 249     return n_point == 0 ? primitive->org : &primitive->data[n_point];
 250 }
 251
 252 /**
 253  * cpml_primitive_get_length:
 254  * @primitive: a #CpmlPrimitive
 255  *
 256  * Abstracts the length() family functions by providing a common
 257  * way to access the underlying primitive-specific implementation.
 258  * The function returns the length of @primitive.
 259  *
 260  * Returns: the requested length or 0 on errors
 261  **/
 262 double
 263 cpml_primitive_get_length(const CpmlPrimitive *primitive)
 264 {
 265     const _CpmlPrimitiveClass *class_data = get_class(primitive);
 266
 267     if (class_data == NULL || class_data->get_length == NULL)
 268         return 0;
 269
 270     return class_data->get_length(primitive);
 271 }
 272
 273 /**
 274  * cpml_primitive_put_extents:
 275  * @primitive: a #CpmlPrimitive
 276  * @extents: where to store the extents
 277  *
 278  * Abstracts the extents() family functions by providing a common
 279  * way to access the underlying primitive-specific implementation.
 280  *
 281  * This function stores in @extents the bounding box of @primitive.
 282  *
 283  * On errors, that is if the extents cannot be calculated for some
 284  * reason, this function does nothing.
 285  **/
 286 void
 287 cpml_primitive_put_extents(const CpmlPrimitive *primitive,
 288                            CpmlExtents *extents)
 289 {
 290     const _CpmlPrimitiveClass *class_data = get_class(primitive);
 291
 292     if (class_data == NULL || class_data->put_extents == NULL)
 293         return;
 294
 295     class_data->put_extents(primitive, extents);
 296 }
 297
 298 /**
 299  * cpml_primitive_put_pair_at:
 300  * @primitive: a #CpmlPrimitive
 301  * @pos:       the position value
 302  * @pair:      the destination #CpmlPair
 303  *
 304  * Abstracts the put_pair_at() family functions by providing a common
 305  * way to access the underlying primitive-specific implementation.
 306  *
 307  * It gets the coordinates of the point lying on @primitive
 308  * at position @pos. @pos is an homogeneous factor where 0 is the
 309  * start point, 1 the end point, 0.5 the mid point and so on.
 310  * @pos can be less than 0 or greater than %1, in which case the
 311  * coordinates of @pair are interpolated.
 312  *
 313  * On errors, that is if the coordinates cannot be calculated for
 314  * some reason, this function does nothing.
 315  **/
 316 void
 317 cpml_primitive_put_pair_at(const CpmlPrimitive *primitive, double pos,
 318                            CpmlPair *pair)
 319 {
 320     const _CpmlPrimitiveClass *class_data = get_class(primitive);
 321
 322     if (class_data == NULL || class_data->put_pair_at == NULL)
 323         return;
 324
 325     class_data->put_pair_at(primitive, pos, pair);
 326 }
 327
 328 /**
 329  * cpml_primitive_put_vector_at:
 330  * @primitive: a #CpmlPrimitive
 331  * @pos:       the position value
 332  * @vector:    the destination #CpmlVector
 333  *
 334  * Abstracts the put_vector_at() family functions by providing a common
 335  * way to access the underlying primitive-specific implementation.
 336  *
 337  * It gets the steepness of the point at position @pos on @primitive.
 338  * @pos is an homogeneous factor where 0 is the start point, 1 the
 339  * end point, 0.5 the mid point and so on.
 340  * @pos can be less than 0 or greater than %1, in which case the
 341  * coordinates of @pair are interpolated.
 342  *
 343  * On errors, that is if the steepness cannot be calculated for
 344  * some reason, this function does nothing.
 345  **/
 346 void
 347 cpml_primitive_put_vector_at(const CpmlPrimitive *primitive, double pos,
 348                              CpmlVector *vector)
 349 {
 350     const _CpmlPrimitiveClass *class_data = get_class(primitive);
 351
 352     if (class_data == NULL || class_data->put_vector_at == NULL)
 353         return;
 354
 355     class_data->put_vector_at(primitive, pos, vector);
 356 }
 357
 358 /**
 359  * cpml_primitive_get_closest_pos:
 360  * @primitive: a #CpmlPrimitive
 361  * @pair:      the coordinates of the subject point
 362  *
 363  * Returns the pos value of the point on @primitive nearest to @pair.
 364  * The returned value is always clamped between %0 and %1.
 365  *
 366  * Returns: the requested pos value between %0 and %1, or %-1 on errors
 367  **/
 368 double
 369 cpml_primitive_get_closest_pos(const CpmlPrimitive *primitive,
 370                                const CpmlPair *pair)
 371 {
 372     const _CpmlPrimitiveClass *class_data = get_class(primitive);
 373
 374     if (class_data == NULL || class_data->get_closest_pos == NULL)
 375         return -1;
 376
 377     return class_data->get_closest_pos(primitive, pair);
 378 }
 379
 380 /**
 381  * cpml_primitive_put_intersections:
 382  * @primitive:  the first #CpmlPrimitive
 383  * @primitive2: the second #CpmlPrimitive
 384  * @n_dest:     maximum number of intersections to return
 385  * @dest:       the destination buffer that can contain @n_dest #CpmlPair
 386  *
 387  * Finds the intersection points between the given primitives and
 388  * returns the result in @dest. The size of @dest should be enough
 389  * to store @n_dest #CpmlPair. The maximum number of intersections
 390  * is dependent on the type of the primitive involved in the
 391  * operation. If there are at least one Bézier curve involved, up to
 392  * %4 intersections could be returned. Otherwise, if there is an arc
 393  * the intersections will be %2 at maximum. For line primitives, there
 394  * is only %1 point (or %0 if the lines are parallel).
 395  *
 396  * <note>
 397  * <para>
 398  * The convention used by the CPML library is that a primitive should
 399  * implement only the intersection algorithms with lower degree
 400  * primitives. This is required to avoid code duplication: intersection
 401  * between arc and Bézier curves must be implemented by #CPML_CURVE and
 402  * intersection between lines and arcs must be implemented by #CPML_ARC.
 403  * cpml_primitive_put_intersections() will take care of swapping the
 404  * arguments if they are not properly ordered.
 405  * </para>
 406  * </note>
 407  *
 408  * Returns: the number of intersection points found or 0 if the
 409  *          primitives do not intersect or on errors
 410  **/
 411 size_t
 412 cpml_primitive_put_intersections(const CpmlPrimitive *primitive,
 413                                  const CpmlPrimitive *primitive2,
 414                                  size_t n_dest, CpmlPair *dest)
 415 {
 416     const _CpmlPrimitiveClass *class_data;
 417     size_t n_points, n_points2;
 418
 419     class_data = get_class(primitive);
 420
 421     if (class_data == NULL || class_data->put_intersections == NULL)
 422         return 0;
 423
 424     n_points = cpml_primitive_get_n_points(primitive);
 425     n_points2 = cpml_primitive_get_n_points(primitive2);
 426
 427     if (n_points == 0 || n_points2 == 0)
 428         return 0;
 429
 430     /* Primitives reordering: the first must be the more complex one */
 431     if (n_points < n_points2) {
 432         const CpmlPrimitive *old_primitive2 = primitive2;
 433         primitive2 = primitive;
 434         primitive = old_primitive2;
 435     }
 436
 437     return class_data->put_intersections(primitive, primitive2, n_dest, dest);
 438 }
 439
 440 /**
 441  * cpml_primitive_put_intersections_with_segment:
 442  * @primitive: a #CpmlPrimitive
 443  * @segment:   a #CpmlSegment
 444  * @n_dest:    maximum number of intersection pairs to return
 445  * @dest:      the destination buffer of #CpmlPair
 446  *
 447  * Computes the intersections between @segment and @primitive by
 448  * sequentially scanning the primitives in @segment and looking
 449  * for their intersections with @primitive.
 450  *
 451  * If the intersections are more than @n_dest, only the first
 452  * @n_dest pairs are stored.
 453  *
 454  * Returns: the number of intersections found
 455  **/
 456 size_t
 457 cpml_primitive_put_intersections_with_segment(const CpmlPrimitive *primitive,
 458                                               const CpmlSegment *segment,
 459                                               size_t n_dest, CpmlPair *dest)
 460 {
 461     CpmlPrimitive portion;
 462     size_t found;
 463
 464     cpml_primitive_from_segment(&portion, (CpmlSegment *) segment);
 465     found = 0;
 466
 467     while (found < n_dest) {
 468         found += cpml_primitive_put_intersections(&portion, primitive,
 469                                                   n_dest-found, dest+found);
 470         if (!cpml_primitive_next(&portion))
 471             break;
 472     }
 473
 474     return found;
 475 }
 476
 477 /**
 478  * cpml_primitive_offset:
 479  * @primitive: a #CpmlPrimitive
 480  * @offset: distance for the computed offset primitive
 481  *
 482  * Given a primitive, computes the same (or approximated) parallel
 483  * primitive distant @offset from the original one and returns
 484  * the result by changing @primitive.
 485  *
 486  * On errors, that is if the offset primitive cannot be calculated
 487  * for some reason, this function does nothing.
 488  **/
 489 void
 490 cpml_primitive_offset(CpmlPrimitive *primitive, double offset)
 491 {
 492     const _CpmlPrimitiveClass *class_data = get_class(primitive);
 493
 494     if (class_data == NULL || class_data->offset == NULL)
 495         return;
 496
 497     return class_data->offset(primitive, offset);
 498 }
 499
 500 /**
 501  * cpml_primitive_join:
 502  * @primitive: the first #CpmlPrimitive
 503  * @primitive2: the second #CpmlPrimitive
 504  *
 505  * Joins two primitive modifying the end point of @primitive and the
 506  * start point of @primitive2 so that the resulting points will overlap.
 507  *
 508  * <important>
 509  * <title>TODO</title>
 510  * <itemizedlist>
 511  * <listitem>Actually, the join is done by extending the end vector
 512  *           of @primitive and the start vector of @primitive2 and
 513  *           interpolating the intersection: this means no primitive
 514  *           dependent code is needed. Anyway, it is likely to change
 515  *           in the future because this approach is quite naive when
 516  *           curves are involved.</listitem>
 517  * </itemizedlist>
 518  * </important>
 519  *
 520  * Returns: 1 on success, 0 if the end vector of @primitive
 521  *          and the start vector of @primitive2 are parallel
 522  **/
 523 cairo_bool_t
 524 cpml_primitive_join(CpmlPrimitive *primitive, CpmlPrimitive *primitive2)
 525 {
 526     cairo_path_data_t *end1, *start2;
 527     CpmlPrimitive line1, line2;
 528     cairo_path_data_t data1[2], data2[2];
 529     CpmlPair joint;
 530
 531     end1 = cpml_primitive_get_point(primitive, -1);
 532     start2 = cpml_primitive_get_point(primitive2, 0);
 533
 534     /* Check if the primitives are yet connected */
 535     if (end1->point.x == start2->point.x && end1->point.y == start2->point.y)
 536         return 1;
 537
 538     line1.org = cpml_primitive_get_point(primitive, -2);
 539     line1.data = data1;
 540     data1[0].header.type = CPML_LINE;
 541     data1[1] = *end1;
 542
 543     line2.org = start2;
 544     line2.data = data2;
 545     data2[0].header.type = CPML_LINE;
 546     data2[1] = *cpml_primitive_get_point(primitive2, 1);
 547
 548     if (!cpml_primitive_put_intersections(&line1, &line2, 1, &joint))
 549         return 0;
 550
 551     cpml_pair_to_cairo(&joint, end1);
 552     cpml_pair_to_cairo(&joint, start2);
 553
 554     return 1;
 555 }
 556
 557 /**
 558  * cpml_primitive_to_cairo:
 559  * @primitive: a #CpmlPrimitive
 560  * @cr: the destination cairo context
 561  *
 562  * Renders a single @primitive to the @cr cairo context.
 563  * As a special case, if the primitive is a #CPML_CLOSE, an
 564  * equivalent line is rendered, because a close path left alone
 565  * is not renderable.
 566  *
 567  * Also a #CPML_ARC primitive is treated specially, as it is not
 568  * natively supported by cairo and has its own rendering API.
 569  **/
 570 void
 571 cpml_primitive_to_cairo(const CpmlPrimitive *primitive, cairo_t *cr)
 572 {
 573     cairo_path_t path;
 574     cairo_path_data_t *path_data;
 575
 576     cairo_move_to(cr, primitive->org->point.x, primitive->org->point.y);
 577
 578     switch (primitive->data->header.type) {
 579
 580     case CPML_CLOSE:
 581         path_data = cpml_primitive_get_point(primitive, -1);
 582         cairo_line_to(cr, path_data->point.x, path_data->point.y);
 583         break;
 584
 585     case CPML_ARC:
 586         cpml_arc_to_cairo(primitive, cr);
 587         break;
 588
 589     default:
 590         path.status = CAIRO_STATUS_SUCCESS;
 591         path.data = primitive->data;
 592         path.num_data = primitive->data->header.length;
 593         cairo_append_path(cr, &path);
 594         break;
 595     }
 596 }
 597
 598 /**
 599  * cpml_primitive_dump:
 600  * @primitive: a #CpmlPrimitive
 601  * @org_also:  whether to output also the origin coordinates
 602  *
 603  * Dumps info on the specified @primitive to stdout: useful for
 604  * debugging purposes. If @org_also is 1, a #CPML_MOVE to the
 605  * origin is prepended to the data otherwise the
 606  * <structfield>org</structfield> field is not used.
 607  **/
 608 void
 609 cpml_primitive_dump(const CpmlPrimitive *primitive, cairo_bool_t org_also)
 610 {
 611     const cairo_path_data_t *data;
 612     int type;
 613     const _CpmlPrimitiveClass *class_data;
 614     size_t n, n_points;
 615
 616     data = primitive->data;
 617     type = data->header.type;
 618     class_data = get_class_from_type(type);
 619
 620     if (class_data == NULL) {
 621         printf("Unknown primitive type (%d)\n", type);
 622         return;
 623     }
 624
 625     /* Dump the origin, if requested */
 626     if (org_also) {
 627         printf("move to ");
 628         dump_cairo_point(primitive->org);
 629         printf("\n");
 630     }
 631
 632     printf("%s ", class_data->name);
 633
 634     n_points = cpml_primitive_get_n_points(primitive);
 635     for (n = 1; n < n_points; ++n)
 636         dump_cairo_point(cpml_primitive_get_point(primitive, n));
 637
 638     printf("\n");
 639 }
 640
 641
 642 static const _CpmlPrimitiveClass *
 643 get_class_from_type(CpmlPrimitiveType type)
 644 {
 645     switch (type) {
 646     case CPML_LINE:
 647         return _cpml_line_get_class();
 648     case CPML_ARC:
 649         return _cpml_arc_get_class();
 650     case CPML_CURVE:
 651         return _cpml_curve_get_class();
 652     case CPML_CLOSE:
 653         return _cpml_close_get_class();
 654     default:
 655         break;
 656     }
 657
 658     return NULL;
 659 }
 660
 661 static const _CpmlPrimitiveClass *
 662 get_class(const CpmlPrimitive *primitive)
 663 {
 664     return get_class_from_type(primitive->data->header.type);
 665 }
 666
 667 static void
 668 dump_cairo_point(const cairo_path_data_t *path_data)
 669 {
 670     printf("(%g %g) ", path_data->point.x, path_data->point.y);
 671 }