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(void)
  13 {
  14         if (debug)
  15                 exit(1);
  16 }
  17
  18 static void validate_subtree(const struct quadtree *node)
  19 {
  20         int i;
  21         long int children;
  22         children = 0;
  23
  24         if (!node) {
  25                 printf("Attempted to validate a null pointer\n");
  26                 fflush(stdout);
  27                 trap();
  28         }
  29
  30         for (i = 0; i < 4; i++) {
  31                 if (!node->child[i])
  32                         continue;
  33
  34                 if (node->child[i]->parent != node) {
  35                         printf("%s:%d Fatal! Tree inconsistency detected at "
  36                                "child %d %p in node %p, incorrent parent %p\n",
  37                                __func__, __LINE__, i, node->child[i], node,
  38                                node->child[i]->parent);
  39                         fflush(stdout);
  40                         trap();
  41                 }
  42
  43                 if (node->parent) {
  44                         if (node->child[i] == node->parent) {
  45                                 printf("%s:%d Fatal! Tree loop detected "
  46                                        "at child %d in node %p\n",
  47                                        __func__, __LINE__, i, node);
  48                                 fflush(stdout);
  49                                 trap();
  50                         }
  51                 }
  52
  53                 children += node->child[i]->children + 1;
  54
  55                 validate_subtree(node->child[i]);
  56         }
  57
  58         if (node->depth < 0) {
  59                 printf("%s:%d Tree statistics inconsistency detected! "
  60                        "Negative depth: %ld\n",
  61                        __func__, __LINE__, node->depth);
  62         }
  63
  64         if (node->children != children) {
  65                 printf("%s:%d Tree statistics inconsistency detected! "
  66                        "child count mismatch. Expected %ld, got %ld\n",
  67                        __func__, __LINE__, children, node->children);
  68                 fflush(stdout);
  69                 trap();
  70         }
  71
  72         for (i = 0; i < 4 && node->children; i++) {
  73                 if (!node->child[i])
  74                         continue;
  75
  76                 if (node->depth == node->child[i]->depth + 1)
  77                         break;
  78
  79                 if (node->child[i]->depth > node->depth) {
  80                         printf("%s:%d Tree statistics inconsistency detected! "
  81                                "child depth mismatch %ld > %ld\n",
  82                                __func__, __LINE__, node->child[i]->depth,
  83                                node->depth);
  84                 }
  85         }
  86
  87         if (i == 4) {
  88                 printf("%s:%d Tree statistics inconsistency detected! "
  89                        "child depth mismatch.",
  90                        __func__, __LINE__);
  91                 fflush(stdout);
  92                 trap();
  93         }
  94 }
  95
  96 static void validate_tree(const struct quadtree *node)
  97 {
  98         if (debug)
  99                 validate_subtree(quadtree_find_parent(node));
 100 }
 101
 102 /**
 103  * quadtree_add - add a node to a quadtree
 104  * @parent: parent node
 105  * @new: the new node to be added
 106  * @compare: pointer to a comparison function
 107  *
 108  * Add a node to a quadtree. The tree is kept in order, the new node
 109  * is placed in the end of appropriate branch. The compare function is
 110  * used to compare the new node against a branch in the tree. The
 111  * comparison function must have following return value depending on
 112  * the position of node a compared to the position of node b:
 113  *
 114  * 0: upper left
 115  * 1: upper right
 116  * 2: lower left
 117  * 3: lower right
 118  *
 119  * The case of nodes sharing identical coordinates is not taken into
 120  * account at all.
 121  */
 122
 123 struct quadtree *quadtree_add(struct quadtree *parent, struct quadtree *new,
 124                               struct quadtree_ops *ops)
 125 {
 126         int ret, i;
 127         if (parent == new)
 128                 trap();
 129
 130         validate_tree(parent);
 131
 132         ret = ops->compare(parent, new);
 133
 134         if (ret < 0 || ret >= 4) {
 135                 printf("Invalid comparison result of %d\n", ret);
 136                 return 0;
 137         }
 138
 139         if (parent->child[ret])
 140                 return quadtree_add(parent->child[ret], new, ops);
 141
 142         parent->child[ret] = new;
 143         new->parent = parent;
 144         for (i = 0; i < 4; i++)
 145                 new->child[i] = 0;
 146
 147         if (debug) {
 148                 printf("adding node %p to parent %p\n", new, parent);
 149                 fflush(stdout);
 150         }
 151
 152         quadtree_recalculate_parent_stats(new, ops);
 153
 154         validate_tree(new);
 155
 156         return new;
 157 }
 158
 159 /*
 160  * _qt_optimal_del - Delete nodes from a detached subtree in optimal order
 161  *
 162  * All nodes are moved under the new parent node
 163  */
 164 static void _qt_optimal_del(struct quadtree *parent, struct quadtree *node,
 165                        struct quadtree_ops *ops, int parents)
 166 {
 167         struct quadtree *child[4] = {0};
 168         int i, children = 0, max_c, max_i;
 169
 170         for (i = 0; i < 4; i++) {
 171                 if (!node->child[i]) {
 172                         child[i] = 0;
 173                         continue;
 174                 }
 175
 176                 child[children] = node->child[i];
 177                 node->child[i] = NULL;
 178                 children++;
 179         }
 180
 181         /*
 182          * Try to remove the nodes in such order that the node which
 183          * has child number one quarter of the parent's child numer
 184          * gets deleted first.
 185          */
 186
 187         if (node->children <= parents / 4) {
 188                 if (debug) {
 189                         printf("%d: Moving node %p away from parent %p\n",
 190                                __LINE__, node, parent);
 191                         fflush(stdout);
 192                 }
 193                 validate_tree(parent);
 194                 quadtree_add(parent, node, ops);
 195                 node = NULL;
 196                 parents /= 4;
 197         }
 198
 199         while(children) {
 200                 max_c = -1;
 201                 max_i = -1;
 202                 for (i = 0; i < 4; i++) {
 203                         if (!child[i])
 204                                 continue;
 205
 206                         if (max_c < child[i]->children) {
 207                                 max_c = child[i]->children;
 208                                 max_i = i;
 209                         }
 210                 }
 211
 212                 _qt_optimal_del(parent, child[max_i], ops, parents / 4);
 213                 child[max_i] = 0;
 214                 children--;
 215         }
 216
 217         if (node) {
 218                 validate_tree(parent);
 219                 if (debug) {
 220                         printf("%d: Moving node %p away from parent %p\n",
 221                                __LINE__, node, parent);
 222                         fflush(stdout);
 223                 }
 224                 quadtree_add(parent, node, ops);
 225         }
 226 }
 227
 228 /*
 229  * quadtree_del - Detach a node from the tree
 230  *
 231  * Return value: The new root node of the tree. If we are detaching
 232  * anything but the root node of the entire tree, the returned root
 233  * value will be the original root of the tree.
 234  */
 235 struct quadtree *quadtree_del(struct quadtree *node,
 236                               struct quadtree_ops *ops)
 237 {
 238         struct quadtree *parent = 0;
 239         int i;
 240
 241         if (debug) {
 242                 printf("Deleting node %p under parent %p\n",
 243                                node, node->parent);
 244                 fflush(stdout);
 245         }
 246         /*
 247          * We are deleting the root node. This means we have to select
 248          * a new root node and reconstruct the entire tree under it
 249          * again.
 250          */
 251         if (!node->parent) {
 252                 for (i = 0; i < 4; i++) {
 253                         if (!node->child[i])
 254                                 continue;
 255
 256                         if (!parent) {
 257                                 parent = node->child[i];
 258                                 parent->parent = 0;
 259                                 continue;
 260                         }
 261                         _qt_optimal_del(parent, node->child[i], ops,
 262                                         node->children);
 263                         node->child[i] = 0;
 264                 }
 265
 266                 return parent;
 267         }
 268
 269         /*
 270          * We are not deleting the parent. Detach the node from the
 271          * parent abd relocate the children. The node will be then
 272          * detached from the tree.
 273          */
 274
 275         for (i = 0; i < 4; i++) {
 276                 if (node->parent->child[i] == node) {
 277                         node->parent->child[i] = 0;
 278                         break;
 279                 }
 280         }
 281         if (i == 4)
 282                 trap();
 283
 284         parent = node->parent;
 285
 286         /*
 287          * The sub branch is now detached from the main tree. Fix the
 288          * stats.
 289          */
 290         quadtree_recalculate_parent_stats(node->parent, ops);
 291
 292         parent = quadtree_find_parent(parent);
 293
 294         if (node->children) {
 295                 for (i = 0; i < 4; i++) {
 296                         if (!node->child[i])
 297                                 continue;
 298
 299                         _qt_optimal_del(parent, node->child[i], ops,
 300                                         node->children);
 301                 }
 302         }
 303
 304         validate_tree(parent);
 305         return parent;
 306 }
 307
 308
 309 static int _walk_tree(struct quadtree *head, const struct quadtree_iterator *it)
 310 {
 311         int direction, count = 0;
 312
 313         direction = it->direction(head, (struct quadtree_iterator *)it);
 314
 315         if ((direction & QUADTREE_UPLEFT) && head->child[0])
 316                 count += _walk_tree(head->child[0], it);
 317
 318         if ((direction & QUADTREE_UPRIGHT) && head->child[1])
 319                 count += _walk_tree(head->child[1], it);
 320
 321         if ((direction & QUADTREE_DOWNLEFT) && head->child[2])
 322                 count += _walk_tree(head->child[2], it);
 323
 324         if ((direction & QUADTREE_DOWNRIGHT) && head->child[3])
 325                 count += _walk_tree(head->child[3], it);
 326
 327         if ((direction & QUADTREE_SELF) && it->callback) {
 328                 it->callback(head, (struct quadtree_iterator *)it);
 329                 count++;
 330         }
 331
 332         return count;
 333 }
 334
 335 int walk_quadtree(const struct quadtree_iterator *it)
 336 {
 337         return _walk_tree(it->head, it);
 338 }