git.itanic.dy.fi Git - sdl-planets/blob - quadtree.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3
   4 #include "quadtree.h"
   5
   6 #ifdef DEBUG
   7 #define debug 1
   8 #else
   9 #define debug 0
  10 #endif
  11
  12 static void _trap(int line)
  13 {
  14         if (debug) {
  15                 printf("Trapped from line %d, use debugger to get backtrace\n",
  16                         line);
  17                 fflush(stdout);
  18                 exit(1);
  19         }
  20 }
  21
  22 #define trap() _trap(__LINE__)
  23
  24 static int quadtree_compare_coord(const struct vector *a,
  25                                 const struct vector *b)
  26 {
  27         int up, left;
  28
  29         up = b->y < a->y;
  30         left = b->x < a->x;
  31
  32         if (up && left)
  33                 return 0;
  34         if (up && !left)
  35                 return 1;
  36         if (left)
  37                 return 2;
  38         return 3;
  39 }
  40
  41 static int quadtree_compare(const struct quadtree *a, const struct quadtree *b)
  42 {
  43         return quadtree_compare_coord(&a->pos, &b->pos);
  44 }
  45
  46 static void validate_subtree(const struct quadtree *node)
  47 {
  48         int i, dir;
  49         long int children;
  50         children = 0;
  51
  52         if (!node) {
  53                 printf("Attempted to validate a null pointer\n");
  54                 fflush(stdout);
  55                 trap();
  56         }
  57
  58         for (i = 0; i < 4; i++) {
  59                 if (!node->child[i])
  60                         continue;
  61
  62                 if (node->child[i]->parent != node) {
  63                         printf("%s:%d Fatal! Tree inconsistency detected at "
  64                                "child %d %p in node %p, incorrent parent %p\n",
  65                                __func__, __LINE__, i, node->child[i], node,
  66                                node->child[i]->parent);
  67                         fflush(stdout);
  68                         trap();
  69                 }
  70
  71                 if (node->parent) {
  72                         if (node->child[i] == node->parent) {
  73                                 printf("%s:%d Fatal! Tree loop detected "
  74                                        "at child %d in node %p\n",
  75                                        __func__, __LINE__, i, node);
  76                                 fflush(stdout);
  77                                 trap();
  78                         }
  79                 }
  80
  81                 dir = quadtree_compare(node, node->child[i]);
  82
  83                 if (dir != i) {
  84                         printf("%s:%d Fatal! Spatial inconsistency detected "
  85                                 "at child %d in node %p\n"
  86                                 "parent: (%f %f), child (%f %f), "
  87                                 "dir %d != %d\n",
  88                                 __func__, __LINE__, i, node,
  89                                 node->pos.x, node->pos.y,
  90                                 node->child[i]->pos.x, node->child[i]->pos.y,
  91                                 dir, i);
  92                         fflush(stdout);
  93                         trap();
  94                 }
  95
  96                 children += node->child[i]->children + 1;
  97
  98                 validate_subtree(node->child[i]);
  99         }
 100
 101         if (node->depth < 0) {
 102                 printf("%s:%d Tree statistics inconsistency detected! "
 103                        "Negative depth: %ld\n",
 104                        __func__, __LINE__, node->depth);
 105         }
 106
 107         if (node->children != children) {
 108                 printf("%s:%d Tree statistics inconsistency detected! "
 109                        "child count mismatch. Expected %ld, got %ld\n",
 110                        __func__, __LINE__, children, node->children);
 111                 fflush(stdout);
 112                 trap();
 113         }
 114
 115         for (i = 0; i < 4 && node->children; i++) {
 116                 if (!node->child[i])
 117                         continue;
 118
 119                 if (node->depth == node->child[i]->depth + 1)
 120                         break;
 121
 122                 if (node->child[i]->depth > node->depth) {
 123                         printf("%s:%d Tree statistics inconsistency detected! "
 124                                "child depth mismatch %ld > %ld\n",
 125                                __func__, __LINE__, node->child[i]->depth,
 126                                node->depth);
 127                 }
 128         }
 129
 130         if (i == 4) {
 131                 printf("%s:%d Tree statistics inconsistency detected! "
 132                        "child depth mismatch.",
 133                        __func__, __LINE__);
 134                 fflush(stdout);
 135                 trap();
 136         }
 137 }
 138
 139 static void validate_tree(const struct quadtree *node)
 140 {
 141         int i;
 142
 143         if (!debug)
 144                 return;
 145
 146         if (!node->parent)
 147                 return validate_subtree(node);
 148
 149         for (i = 0; i < 4; i++)
 150                 if (node->parent->child[i] == node)
 151                         break;
 152
 153         if (i == 4) {
 154                 printf("%s:%d Tree inconsistency detected! "
 155                         "Wrong parent %p for node %p\n",
 156                         __func__, __LINE__, node->parent, node);
 157                 fflush(stdout);
 158                 trap();
 159         }
 160
 161         validate_tree(node->parent);
 162 }
 163
 164 void _quadtree_validate_tree(const struct quadtree *node)
 165 {
 166         validate_tree(node);
 167 }
 168
 169 static struct quadtree *_quadtree_add(struct quadtree *parent,
 170                                 struct quadtree *new)
 171 {
 172         int ret, i;
 173
 174         ret = quadtree_compare(parent, new);
 175
 176         if (ret < 0 || ret >= 4) {
 177                 printf("Invalid comparison result of %d\n", ret);
 178                 return 0;
 179         }
 180
 181         if (parent->child[ret])
 182                 return _quadtree_add(parent->child[ret], new);
 183
 184         parent->child[ret] = new;
 185         new->parent = parent;
 186         for (i = 0; i < 4; i++)
 187                 new->child[i] = 0;
 188
 189         return new;
 190 }
 191
 192 static void _recalculate_node_area_stats(struct quadtree *node)
 193 {
 194                 /* The space covered by the parent node's corner
 195                  * points needs be as wide as its widest child node's
 196                  * corners.
 197                  */
 198 #define CHILD_CORNER_SAFE(node, ch_idx, cor_idx, axis)          \
 199         ((node)->child[ch_idx] ?                                \
 200                 (node)->child[ch_idx]->corner[cor_idx].axis :   \
 201                 (node)->pos.axis)
 202
 203                 node->corner[0].x = MIN(CHILD_CORNER_SAFE(node, 0, 0, x),
 204                                         CHILD_CORNER_SAFE(node, 2, 0, x));
 205                 node->corner[0].y = MIN(CHILD_CORNER_SAFE(node, 0, 0, y),
 206                                         CHILD_CORNER_SAFE(node, 1, 0, y));
 207                 node->corner[1].x = MAX(CHILD_CORNER_SAFE(node, 1, 1, x),
 208                                         CHILD_CORNER_SAFE(node, 3, 1, x));
 209                 node->corner[1].y = MAX(CHILD_CORNER_SAFE(node, 2, 1, y),
 210                                         CHILD_CORNER_SAFE(node, 3, 1, y));
 211 #undef CHILD_CORNER_SAFE
 212 }
 213
 214 static void recalculate_parent_area_stats(struct quadtree *node)
 215 {
 216         while (node) {
 217                 _recalculate_node_area_stats(node);
 218
 219                 node = node->parent;
 220         }
 221 }
 222
 223 /*
 224  * Recursively walk through the tree and propagate changes made to the
 225  * given node up until the highest parent.
 226  */
 227 static void quadtree_recalculate_parent_stats(struct quadtree *node,
 228                                                      struct quadtree_ops *ops)
 229 {
 230         int i;
 231
 232         while (node) {
 233                 node->depth = 0;
 234                 node->children = 0;
 235
 236                 for (i = 0; i < 4; i++) {
 237                         if (!node->child[i])
 238                                 continue;
 239
 240                         node->depth = MAX(node->depth,
 241                                           node->child[i]->depth + 1);
 242                         node->children += node->child[i]->children + 1;
 243                 }
 244
 245                 _recalculate_node_area_stats(node);
 246
 247                 if (ops->recalculate_stats)
 248                         ops->recalculate_stats(node);
 249
 250                 node = node->parent;
 251         }
 252 }
 253
 254 /**
 255  * quadtree_add - add a node to a quadtree
 256  * @parent: parent node
 257  * @new: the new node to be added
 258  *
 259  * Add a node to a quadtree. The tree is kept in order, the new node
 260  * is placed in the end of appropriate branch.
 261  *
 262  * The case of nodes sharing identical coordinates is not taken into
 263  * account at all.
 264  */
 265
 266 struct quadtree *quadtree_add(struct quadtree *parent, struct quadtree *new,
 267                               struct quadtree_ops *ops)
 268 {
 269         if (parent == new)
 270                 trap();
 271
 272         validate_tree(parent);
 273
 274         _quadtree_add(parent, new);
 275
 276         if (debug) {
 277                 printf("adding node %p to parent %p\n", new, parent);
 278                 fflush(stdout);
 279         }
 280
 281         quadtree_recalculate_parent_stats(new, ops);
 282
 283         validate_tree(new);
 284
 285         return new;
 286 }
 287
 288 static int is_within(struct vector *pos, struct vector *corner)
 289 {
 290         if ((pos->x >= corner[1].x) && (pos->x <= corner[0].x) &&
 291             (pos->y >= corner[1].y) && (pos->y <= corner[0].y))
 292                 return 1;
 293         return 0;
 294 }
 295
 296 static int quadrants_to_search(struct quadtree *node, struct vector *corner)
 297 {
 298         int direction = 0, i;
 299         int up = 0, left = 0, right = 0, down = 0;
 300
 301         for (i = 0; i < 2; i++) {
 302                 if (corner[i].x <= node->pos.x)
 303                         left = 1;
 304                 else if (corner[i].x >= node->pos.x)
 305                         right = 1;
 306                 if (corner[i].y <= node->pos.y)
 307                         up = 1;
 308                 else if (corner[i].y >= node->pos.y)
 309                         down = 1;
 310         }
 311
 312         if (left || up)
 313                 direction |= QUADTREE_UPLEFT;
 314         if (right || up)
 315                 direction |= QUADTREE_UPRIGHT;
 316         if (left || down)
 317                 direction |= QUADTREE_DOWNLEFT;
 318         if (right || down)
 319                 direction |= QUADTREE_DOWNRIGHT;
 320
 321         return direction;
 322 }
 323
 324 static struct quadtree *quadtree_find_nearest(struct quadtree *tree,
 325                                         struct vector *pos,
 326                                         struct vector *corner)
 327 {
 328         struct vector tmp;
 329         struct quadtree *nearest, *node;
 330         double distance = 0, dist;
 331         int i, directions;
 332
 333         if (!is_within(pos, corner)) {
 334                 if (debug) {
 335                         printf("No nearest to be found from (%f %f) (%f %f) "
 336                                 "pos (%f %f)\n",
 337                                 corner[0].x, corner[0].y,
 338                                 corner[1].x, corner[1].y,
 339                                 pos->x, pos->y);
 340                         fflush(stdout);
 341                 }
 342                 return NULL;
 343         }
 344
 345         if (is_within(&tree->pos, corner)) {
 346                 vector_sub(pos, &tree->pos, &tmp);
 347                 distance = vector_abs(&tmp);
 348                 nearest = tree;
 349         } else {
 350                 nearest = NULL;
 351         }
 352
 353         directions = quadrants_to_search(tree, corner);
 354
 355         for (i = 0; i < 4; i++) {
 356                 if (!tree->child[i])
 357                         continue;
 358
 359 /*
 360                 if (!(directions & (1 << i)))
 361                         continue;
 362 */
 363                 node = quadtree_find_nearest(tree->child[i], pos, corner);
 364
 365                 if (!node)
 366                         continue;
 367
 368                 vector_sub(pos, &node->pos, &tmp);
 369                 dist = vector_abs(&tmp);
 370
 371                 if (!nearest || dist < distance) {
 372                         nearest = node;
 373                         distance = dist;
 374
 375                 }
 376         }
 377
 378         if (nearest && !is_within(&nearest->pos, corner)) {
 379                 if (debug)
 380                         printf("Node %p (%f %f) is not within "
 381                                 "search window (%f %f) (%f %f)\n",
 382                                 nearest, nearest->pos.x, nearest->pos.y,
 383                                 corner[0].x, corner[0].y,
 384                                 corner[1].x, corner[1].y);
 385                 return NULL;
 386         }
 387
 388         return nearest;
 389 }
 390
 391 static struct quadtree *quadtree_find_nearest_noparent(struct quadtree *tree,
 392                                                 struct vector *pos,
 393                                                 struct vector *corner)
 394 {
 395         struct quadtree *nearest;
 396         struct vector sub;
 397         struct quadtree *node;
 398         double dist = 0, dist2;
 399         int i;
 400
 401         nearest = quadtree_find_nearest(tree, pos, corner);
 402
 403         if (nearest != tree)
 404                 goto out;
 405
 406         if (debug)
 407                 printf("Avoiding parent or NULL node %p\n", nearest);
 408
 409         /*
 410          * oops, we don't want to pick the parent node, let's choose
 411          * another one
 412          */
 413         nearest = NULL;
 414         for (i = 0; i < 4; i++) {
 415                 if (!tree->child[i])
 416                         continue;
 417
 418                 if (!nearest) {
 419                         nearest = quadtree_find_nearest(tree->child[i], pos,
 420                                                         corner);
 421
 422                         if (nearest == NULL)
 423                                 continue;
 424
 425                         vector_sub(pos, &nearest->pos, &sub);
 426                         dist = vector_abs(&sub);
 427                         continue;
 428                 }
 429                 node = quadtree_find_nearest(tree->child[i],
 430                                         pos, corner);
 431
 432                 if (node == NULL)
 433                         continue;
 434
 435                 vector_sub(pos, &node->pos, &sub);
 436                 dist2 = vector_abs(&sub);
 437
 438                 if (dist2 < dist) {
 439                         nearest = node;
 440                         dist = dist2;
 441                 }
 442         }
 443
 444 out:
 445         return nearest;
 446 }
 447
 448 static void get_middle_point(struct vector *corner, struct vector *middle)
 449 {
 450         middle->x = (corner[0].x + corner[1].x) / (double)2;
 451         middle->y = (corner[0].y + corner[1].y) / (double)2;
 452 }
 453
 454 static int quadtree_split_by_node(struct quadtree *node,
 455                                 struct vector *corner, int dir)
 456 {
 457         if (!is_within(&node->pos, corner)) {
 458                 if (debug)
 459                         printf("Not within search rectangle\n");
 460                 return 0;
 461         }
 462
 463         switch (dir) {
 464         case QUADTREE_UPLEFT:
 465                 corner[0] = node->pos;
 466                 break;
 467         case QUADTREE_UPRIGHT:
 468                 corner[0].y = node->pos.y;
 469                 corner[1].x = node->pos.x;
 470                 break;
 471         case QUADTREE_DOWNRIGHT:
 472                 corner[1] = node->pos;
 473                 break;
 474         case QUADTREE_DOWNLEFT:
 475                 corner[0].x = node->pos.x;
 476                 corner[1].y = node->pos.y;
 477                 break;
 478         default:
 479                 trap();
 480         }
 481
 482         if (debug)
 483                 printf("Search rectangle is now (%f %f) (%f %f), (%f %f)\n",
 484                         corner[0].x, corner[0].y,
 485                         corner[1].x, corner[1].y,
 486                         node->pos.x, node->pos.y);
 487
 488         if ((corner[0].x < corner[1].x) ||
 489             (corner[0].y < corner[1].y))
 490                 trap();
 491
 492         return 1;
 493 }
 494
 495 /*
 496  * Quickly detach a node from a tree. Move all child nodes under
 497  * @parent node.
 498  */
 499 static int _quadtree_del(struct quadtree *node, struct quadtree *parent)
 500 {
 501         struct quadtree *n;
 502         int i;
 503
 504         /* Detach from the tree */
 505         if (node->parent)
 506                 for (i = 0; i < 4; i++) {
 507                         if (node->parent->child[i] == node) {
 508                                 node->parent->child[i] = 0;
 509                                 break;
 510                         }
 511                 }
 512
 513         if (i == 4)
 514                 trap();
 515
 516
 517         for (i = 0; i < 4; i++) {
 518                 if (!node->child[i])
 519                         continue;
 520
 521                 n = node->child[i];
 522                 _quadtree_del(n, parent);
 523                 _quadtree_add(parent, n);
 524         }
 525
 526         return 0;
 527 }
 528
 529 /**
 530  * Move everything under @tree node to @parent node, everything
 531  * else except the @tree node itself
 532  */
 533 static int optimally_move_tree(struct quadtree *tree, struct quadtree *parent,
 534                         struct vector *corner_orig,
 535                         struct quadtree_ops *ops)
 536 {
 537         struct vector corner[2], mid;
 538         struct quadtree *t, *tmp;
 539         int moved = 0;
 540
 541         get_middle_point(corner_orig, &mid);
 542         t = quadtree_find_nearest_noparent(tree, &mid, corner_orig);
 543
 544         if (!t) {
 545                 if (debug)
 546                         printf("Cannot find nearest node\n");
 547
 548                 goto out;
 549         }
 550
 551         /*
 552          * Now we have the t node which contains the object of the
 553          * spatial middle coordinates of the tree.
 554          */
 555
 556         if (debug) {
 557                 printf("Relocating node %p (%f %f) under parent %p\n", t,
 558                         t->pos.x, t->pos.y, parent);
 559                 printf("There are %ld child nodes left\n", tree->children);
 560                 fflush(stdout);
 561         }
 562         _quadtree_del(t, tree);
 563         quadtree_add(parent, t, ops);
 564
 565         moved++;
 566         tree->children--;
 567         if (!tree->children)
 568                 goto out;
 569
 570         /*
 571          * Now split the search rectangle in quadtres and do the same
 572          * with all of the quarters.
 573          */
 574
 575         corner[0] = corner_orig[0];
 576         corner[1] = corner_orig[1];
 577         if (quadtree_split_by_node(t, corner, QUADTREE_UPLEFT))
 578                 moved += optimally_move_tree(tree, parent, corner, ops);
 579
 580         corner[0] = corner_orig[0];
 581         corner[1] = corner_orig[1];
 582         if (quadtree_split_by_node(t, corner, QUADTREE_UPRIGHT))
 583                 moved += optimally_move_tree(tree, parent, corner, ops);
 584
 585         corner[0] = corner_orig[0];
 586         corner[1] = corner_orig[1];
 587         if (quadtree_split_by_node(t, corner, QUADTREE_DOWNLEFT))
 588                 moved += optimally_move_tree(tree, parent, corner, ops);
 589
 590         corner[0] = corner_orig[0];
 591         corner[1] = corner_orig[1];
 592         if (quadtree_split_by_node(t, corner, QUADTREE_DOWNRIGHT))
 593                 moved += optimally_move_tree(tree, parent, corner, ops);
 594
 595         get_middle_point(corner_orig, &mid);
 596         tmp = quadtree_find_nearest(tree, &mid, corner_orig);
 597         if (tmp && tmp != tree)
 598                 trap();
 599
 600 out:
 601         if (debug)
 602                 printf("Now moved %d nodes, %ld left\n", moved, tree->children);
 603
 604         return moved;
 605 }
 606
 607 /*
 608  * quadtree_del - Detach a node from the tree
 609  *
 610  * Return value: The new root node of the tree. If we are detaching
 611  * anything but the root node of the entire tree, the returned root
 612  * value will be the original root of the tree.
 613  */
 614 struct quadtree *quadtree_del(struct quadtree *node,
 615                               struct quadtree_ops *ops)
 616 {
 617         struct quadtree *parent = NULL;
 618         struct vector corner[2];
 619         int i, children = node->children, moved;
 620
 621         validate_tree(node);
 622
 623         if (debug) {
 624                 printf("Deleting node %p under parent %p\n",
 625                                node, node->parent);
 626                 printf("Relocating %ld children\n", node->children);
 627                 fflush(stdout);
 628         }
 629
 630         if (!node->parent) {
 631                 /*
 632                  * We are deleting the root node. This means we have
 633                  * to select a new root node and reconstruct the
 634                  * entire tree under it again.
 635                  */
 636                 if (debug) {
 637                         printf("Deleting root node\n");
 638                         fflush(stdout);
 639                 }
 640                 for (i = 0; i < 4; i++) {
 641                         if (!node->child[i])
 642                                 continue;
 643
 644                         parent = node->child[i];
 645                         _quadtree_del(parent, node);
 646                         parent->parent = 0;
 647                         quadtree_recalculate_parent_stats(parent, ops);
 648                         break;
 649                 }
 650         } else {
 651                 /*
 652                  * The node has a parent. Detach the node from it and
 653                  * relocate the children.
 654                  */
 655
 656                 for (i = 0; i < 4; i++) {
 657                         if (node->parent->child[i] == node) {
 658                                 node->parent->child[i] = 0;
 659                                 break;
 660                         }
 661                 }
 662                 if (i == 4)
 663                         trap();
 664
 665                 parent = node->parent;
 666
 667                 /*
 668                  * The sub branch is now detached from the main
 669                  * tree. Fix the stats.
 670                  */
 671                 quadtree_recalculate_parent_stats(node->parent, ops);
 672         }
 673
 674         validate_tree(parent);
 675
 676         if (!node->children)
 677                 goto out;
 678         /*
 679          * Now we are ready to prepare for relocating the nodes under
 680          * the parent.
 681          */
 682
 683         corner[0] = node->corner[1];
 684         corner[1] = node->corner[0];
 685         moved = optimally_move_tree(node, parent, corner, ops);
 686
 687         if (debug) {
 688                 if (moved != children) {
 689                         printf("Got %d children but %d were moved\n",
 690                                 children, moved);
 691                         printf("nearest children left:\n");
 692                         for (i = 0 ; i < 4; i++)
 693                                 if (node->child[i])
 694                                         printf("   node %d %p, (%f %f)\n",
 695                                                 i, node->child[i],
 696                                                 node->child[i]->pos.x,
 697                                                 node->child[i]->pos.y);
 698                         fflush(stdout);
 699                         trap();
 700                 }
 701                 printf("Delete done, returning parent %p\n", parent);
 702                 fflush(stdout);
 703         }
 704
 705 out:
 706         validate_tree(parent);
 707         return quadtree_find_parent(parent);
 708 }
 709
 710 static void check_for_crossed_subnodes(struct quadtree *node,
 711                                 struct vector *limit, struct quadtree_ops *ops)
 712 {
 713         int direction = 0, i;
 714         int up = 0, left = 0, right = 0, down = 0;
 715
 716         for (i = 0; i < 2; i++) {
 717                 if (limit[i].x < node->pos.x)
 718                         left = 1;
 719                 else
 720                         right = 1;
 721                 if (limit[i].y < node->pos.y)
 722                         up = 1;
 723                 else
 724                         down = 1;
 725         }
 726
 727         if (left || up)
 728                 direction |= QUADTREE_UPLEFT;
 729         if (right || up)
 730                 direction |= QUADTREE_UPRIGHT;
 731         if (left || down)
 732                 direction |= QUADTREE_DOWNLEFT;
 733         if (right || down)
 734                 direction |= QUADTREE_DOWNRIGHT;
 735         if ((left && right) || (up && down))
 736                 direction |= QUADTREE_SELF;
 737
 738         if ((direction & QUADTREE_UPLEFT) && node->child[0])
 739                 check_for_crossed_subnodes(node->child[0], limit, ops);
 740
 741         if ((direction & QUADTREE_UPRIGHT) && node->child[1])
 742                 check_for_crossed_subnodes(node->child[0], limit, ops);
 743
 744         if ((direction & QUADTREE_DOWNLEFT) && node->child[2])
 745                 check_for_crossed_subnodes(node->child[0], limit, ops);
 746
 747         if ((direction & QUADTREE_DOWNRIGHT) && node->child[3])
 748                 check_for_crossed_subnodes(node->child[0], limit, ops);
 749
 750         if (direction & QUADTREE_SELF) {
 751                 struct quadtree *parent;
 752
 753                 parent = quadtree_del(node, ops);
 754                 quadtree_add(parent, node, ops);
 755         }
 756 }
 757
 758 struct quadtree *quadtree_move(struct quadtree *node, struct vector new_pos,
 759                         struct quadtree_ops *ops)
 760 {
 761         struct quadtree *parent, *tree_parent;
 762         int modify;
 763
 764         /* Check if we have crossed any of the parents */
 765         parent = node->parent;
 766         while (parent) {
 767                 if (node->pos.x < parent->pos.x && new_pos.x > parent->pos.x)
 768                         modify = 1;
 769                 if (node->pos.x > parent->pos.x && new_pos.x < parent->pos.x)
 770                         modify = 1;
 771                 if (node->pos.y < parent->pos.y && new_pos.y > parent->pos.y)
 772                         modify = 1;
 773                 if (node->pos.y > parent->pos.y && new_pos.y < parent->pos.y)
 774                         modify = 1;
 775
 776                 if (!modify) {
 777                         parent = parent->parent;
 778                         continue;
 779                 }
 780
 781                 /*
 782                  * If the node has crossed the boundaries, remove it
 783                  * from the tree and add it again to it. It is then
 784                  * guaranteed to be in the correct position of the
 785                  * tree.
 786                  */
 787                 tree_parent = quadtree_del(node, ops);
 788                 node->pos = new_pos;
 789                 quadtree_add(tree_parent, node, ops);
 790                 quadtree_recalculate_parent_stats(node, ops);
 791                 return tree_parent;
 792         }
 793
 794         /* Move the node into its new location */
 795         node->pos = new_pos;
 796
 797         if(node->children) {
 798                 /*
 799                  * Now, search the subtree for any children that are
 800                  * located in wrong place and move them into correct
 801                  * place within the tree.
 802                  */
 803                 struct vector limit[2];
 804
 805                 limit[0] = node->pos;
 806                 limit[1] = new_pos;
 807                 check_for_crossed_subnodes(node, limit, ops);
 808         }
 809
 810         quadtree_recalculate_parent_stats(node, ops);
 811         return quadtree_find_parent(node);
 812
 813 }
 814
 815 static int _walk_tree(struct quadtree *head, const struct quadtree_iterator *it)
 816 {
 817         int direction, count = 0;
 818
 819         direction = it->direction(head, (struct quadtree_iterator *)it);
 820
 821         if ((direction & QUADTREE_UPLEFT) && head->child[0])
 822                 count += _walk_tree(head->child[0], it);
 823
 824         if ((direction & QUADTREE_UPRIGHT) && head->child[1])
 825                 count += _walk_tree(head->child[1], it);
 826
 827         if ((direction & QUADTREE_DOWNLEFT) && head->child[2])
 828                 count += _walk_tree(head->child[2], it);
 829
 830         if ((direction & QUADTREE_DOWNRIGHT) && head->child[3])
 831                 count += _walk_tree(head->child[3], it);
 832
 833         if ((direction & QUADTREE_SELF) && it->callback) {
 834                 it->callback(head, (struct quadtree_iterator *)it);
 835                 count++;
 836         }
 837
 838         return count;
 839 }
 840
 841 int walk_quadtree(const struct quadtree_iterator *it)
 842 {
 843         return _walk_tree(it->head, it);
 844 }