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;
 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
 145         if (debug) {
 146                 printf("adding node %p to parent %p\n", new, parent);
 147                 fflush(stdout);
 148         }
 149
 150         quadtree_recalculate_parent_stats(new, ops);
 151
 152         validate_tree(new);
 153
 154         return new;
 155 }
 156
 157 /*
 158  * _quadtree_reposition_reqursively - Move everything under and
 159  * including a given node under the new root node
 160  */
 161
 162 static void
 163 _quadtree_reposition_reqursively(struct quadtree *root,
 164                                  struct quadtree *node,
 165                                  struct quadtree_ops *ops)
 166 {
 167         int i;
 168
 169         validate_tree(root);
 170
 171         /* First remove all children, if any */
 172
 173         for (i = 0; i < 4; i++) {
 174                 if (!node->child[i])
 175                         continue;
 176
 177                 if (node->child[i] == node ||
 178                     node->child[i] == node->parent)
 179                         trap();
 180
 181                 _quadtree_reposition_reqursively(root, node->child[i], ops);
 182                 node->child[i] = 0;
 183         }
 184
 185         /* There are no children left, reset stats */
 186         node->depth = 0;
 187         node->children = 0;
 188
 189         /* Then remove this node under the new root. */
 190         quadtree_add(root, node, ops);
 191 }
 192
 193 /*
 194  * quadtree_del - Detach a node from the tree
 195  *
 196  * Return value: The new root node of the tree. If we are detaching
 197  * anything but the root node of the entire tree, the returned root
 198  * value will be the original root of the tree.
 199  */
 200 struct quadtree *quadtree_del(struct quadtree *node,
 201                               struct quadtree_ops *ops)
 202 {
 203         struct quadtree *parent = 0;
 204         int i;
 205
 206         if (debug) {
 207                 printf("Deleting node %p under parent %p\n",
 208                                node, node->parent);
 209                 fflush(stdout);
 210         }
 211         /*
 212          * We are deleting the root node. This means we have to select
 213          * a new root node and reconstruct the entire tree under it
 214          * again.
 215          */
 216         if (!node->parent) {
 217                 for (i = 0; i < 4; i++) {
 218                         if (!node->child[i])
 219                                 continue;
 220
 221                         if (!parent) {
 222                                 parent = node->child[i];
 223                                 parent->parent = 0;
 224                                 continue;
 225                         }
 226                         _quadtree_reposition_reqursively(parent,
 227                                                          node->child[i],
 228                                                          ops);
 229                         node->child[i] = 0;
 230                 }
 231
 232                 return parent;
 233         }
 234
 235         /*
 236          * We are not deleting the parent. Detach the node from the
 237          * parent abd relocate the children. The node will be then
 238          * detached from the tree.
 239          */
 240
 241         for (i = 0; i < 4; i++) {
 242                 if (node->parent->child[i] == node) {
 243                         node->parent->child[i] = 0;
 244                         break;
 245                 }
 246         }
 247         if (i == 4) {
 248                 printf("%s:%d Fatal! Tree inconsistency detected\n",
 249                        __func__, __LINE__);
 250                 trap();
 251         }
 252
 253         /* Fix parent stats */
 254         quadtree_recalculate_parent_stats(node->parent, ops);
 255
 256         /*
 257          * The sub branch is now detached from the main tree. Continue
 258          * relocating the detached branch.
 259          */
 260
 261         for (i = 0; i < 4; i++) {
 262                 if (!node->child[i])
 263                         continue;
 264
 265                 _quadtree_reposition_reqursively(node->parent, node->child[i],
 266                                                  ops);
 267                 node->child[i] = 0;
 268         }
 269
 270         parent = quadtree_find_parent(node);
 271         node->parent = 0;
 272
 273         node->children = 0;
 274         node->depth = 0;
 275
 276         validate_tree(parent);
 277         return parent;
 278 }
 279
 280
 281 static int _walk_tree(struct quadtree *head, const struct quadtree_iterator *it)
 282 {
 283         int direction, count = 0;
 284
 285         direction = it->direction(head, (struct quadtree_iterator *)it);
 286
 287         if ((direction & QUADTREE_UPLEFT) && head->child[0])
 288                 count += _walk_tree(head->child[0], it);
 289
 290         if ((direction & QUADTREE_UPRIGHT) && head->child[1])
 291                 count += _walk_tree(head->child[1], it);
 292
 293         if ((direction & QUADTREE_DOWNLEFT) && head->child[2])
 294                 count += _walk_tree(head->child[2], it);
 295
 296         if ((direction & QUADTREE_DOWNRIGHT) && head->child[3])
 297                 count += _walk_tree(head->child[3], it);
 298
 299         if ((direction & QUADTREE_SELF) && it->callback) {
 300                 it->callback(head, (struct quadtree_iterator *)it);
 301                 count++;
 302         }
 303
 304         return count;
 305 }
 306
 307 int walk_quadtree(const struct quadtree_iterator *it)
 308 {
 309         return _walk_tree(it->head, it);
 310 }