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         if (debug)
 142                 validate_subtree(quadtree_find_parent(node));
 143 }
 144
 145 /**
 146  * quadtree_add - add a node to a quadtree
 147  * @parent: parent node
 148  * @new: the new node to be added
 149  *
 150  * Add a node to a quadtree. The tree is kept in order, the new node
 151  * is placed in the end of appropriate branch.
 152  *
 153  * The case of nodes sharing identical coordinates is not taken into
 154  * account at all.
 155  */
 156
 157 struct quadtree *quadtree_add(struct quadtree *parent, struct quadtree *new,
 158                               struct quadtree_ops *ops)
 159 {
 160         int ret, i;
 161         if (parent == new)
 162                 trap();
 163
 164         validate_tree(parent);
 165
 166         ret = quadtree_compare(parent, new);
 167
 168         if (ret < 0 || ret >= 4) {
 169                 printf("Invalid comparison result of %d\n", ret);
 170                 return 0;
 171         }
 172
 173         if (parent->child[ret])
 174                 return quadtree_add(parent->child[ret], new, ops);
 175
 176         parent->child[ret] = new;
 177         new->parent = parent;
 178         for (i = 0; i < 4; i++)
 179                 new->child[i] = 0;
 180
 181         if (debug) {
 182                 printf("adding node %p to parent %p\n", new, parent);
 183                 fflush(stdout);
 184         }
 185
 186         quadtree_recalculate_parent_stats(new, ops);
 187
 188         validate_tree(new);
 189
 190         return new;
 191 }
 192
 193 /*
 194  * _qt_optimal_del - Delete nodes from a detached subtree in optimal order
 195  *
 196  * All nodes are moved under the new parent node
 197  */
 198 static void _qt_optimal_del(struct quadtree *parent, struct quadtree *node,
 199                        struct quadtree_ops *ops, int parents)
 200 {
 201         struct quadtree *child[4] = {0};
 202         int i, children = 0, max_c, max_i;
 203
 204         for (i = 0; i < 4; i++) {
 205                 if (!node->child[i]) {
 206                         child[i] = 0;
 207                         continue;
 208                 }
 209
 210                 child[children] = node->child[i];
 211                 node->child[i] = NULL;
 212                 children++;
 213         }
 214
 215         /*
 216          * Try to remove the nodes in such order that the node which
 217          * has child number one quarter of the parent's child numer
 218          * gets deleted first.
 219          */
 220
 221         if (node->children <= parents / 4) {
 222                 if (debug) {
 223                         printf("%d: Moving node %p away from parent %p\n",
 224                                __LINE__, node, parent);
 225                         fflush(stdout);
 226                 }
 227                 validate_tree(parent);
 228                 quadtree_add(parent, node, ops);
 229                 node = NULL;
 230                 parents /= 4;
 231         }
 232
 233         while(children) {
 234                 max_c = -1;
 235                 max_i = -1;
 236                 for (i = 0; i < 4; i++) {
 237                         if (!child[i])
 238                                 continue;
 239
 240                         if (max_c < child[i]->children) {
 241                                 max_c = child[i]->children;
 242                                 max_i = i;
 243                         }
 244                 }
 245
 246                 _qt_optimal_del(parent, child[max_i], ops, parents / 4);
 247                 child[max_i] = 0;
 248                 children--;
 249         }
 250
 251         if (node) {
 252                 validate_tree(parent);
 253                 if (debug) {
 254                         printf("%d: Moving node %p away from parent %p\n",
 255                                __LINE__, node, parent);
 256                         fflush(stdout);
 257                 }
 258                 quadtree_add(parent, node, ops);
 259         }
 260 }
 261
 262 /*
 263  * quadtree_del - Detach a node from the tree
 264  *
 265  * Return value: The new root node of the tree. If we are detaching
 266  * anything but the root node of the entire tree, the returned root
 267  * value will be the original root of the tree.
 268  */
 269 struct quadtree *quadtree_del(struct quadtree *node,
 270                               struct quadtree_ops *ops)
 271 {
 272         struct quadtree *parent = 0;
 273         int i;
 274
 275         if (debug) {
 276                 printf("Deleting node %p under parent %p\n",
 277                                node, node->parent);
 278                 fflush(stdout);
 279         }
 280         /*
 281          * We are deleting the root node. This means we have to select
 282          * a new root node and reconstruct the entire tree under it
 283          * again.
 284          */
 285         if (!node->parent) {
 286                 for (i = 0; i < 4; i++) {
 287                         if (!node->child[i])
 288                                 continue;
 289
 290                         if (!parent) {
 291                                 parent = node->child[i];
 292                                 parent->parent = 0;
 293                                 continue;
 294                         }
 295                         _qt_optimal_del(parent, node->child[i], ops,
 296                                         node->children);
 297                         node->child[i] = 0;
 298                 }
 299
 300                 return parent;
 301         }
 302
 303         /*
 304          * We are not deleting the parent. Detach the node from the
 305          * parent abd relocate the children. The node will be then
 306          * detached from the tree.
 307          */
 308
 309         for (i = 0; i < 4; i++) {
 310                 if (node->parent->child[i] == node) {
 311                         node->parent->child[i] = 0;
 312                         break;
 313                 }
 314         }
 315         if (i == 4)
 316                 trap();
 317
 318         parent = node->parent;
 319
 320         /*
 321          * The sub branch is now detached from the main tree. Fix the
 322          * stats.
 323          */
 324         quadtree_recalculate_parent_stats(node->parent, ops);
 325
 326         parent = quadtree_find_parent(parent);
 327
 328         if (node->children) {
 329                 for (i = 0; i < 4; i++) {
 330                         if (!node->child[i])
 331                                 continue;
 332
 333                         _qt_optimal_del(parent, node->child[i], ops,
 334                                         node->children);
 335                 }
 336         }
 337
 338         validate_tree(parent);
 339         return parent;
 340 }
 341
 342
 343 static int _walk_tree(struct quadtree *head, const struct quadtree_iterator *it)
 344 {
 345         int direction, count = 0;
 346
 347         direction = it->direction(head, (struct quadtree_iterator *)it);
 348
 349         if ((direction & QUADTREE_UPLEFT) && head->child[0])
 350                 count += _walk_tree(head->child[0], it);
 351
 352         if ((direction & QUADTREE_UPRIGHT) && head->child[1])
 353                 count += _walk_tree(head->child[1], it);
 354
 355         if ((direction & QUADTREE_DOWNLEFT) && head->child[2])
 356                 count += _walk_tree(head->child[2], it);
 357
 358         if ((direction & QUADTREE_DOWNRIGHT) && head->child[3])
 359                 count += _walk_tree(head->child[3], it);
 360
 361         if ((direction & QUADTREE_SELF) && it->callback) {
 362                 it->callback(head, (struct quadtree_iterator *)it);
 363                 count++;
 364         }
 365
 366         return count;
 367 }
 368
 369 int walk_quadtree(const struct quadtree_iterator *it)
 370 {
 371         return _walk_tree(it->head, it);
 372 }