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         for (i = 0; i < 4; i++) {
  25                 if (!node->child[i])
  26                         continue;
  27
  28                 if (node->child[i]->parent != node) {
  29                         printf("%s:%d Fatal! Tree inconsistency detected "
  30                                "at child %d in node %p\n",
  31                                __func__, __LINE__, i, node);
  32                         trap();
  33                 }
  34
  35                 if (node->parent) {
  36                         if (node->child[i] == node->parent) {
  37                                 printf("%s:%d Fatal! Tree loop detected "
  38                                        "at child %d in node %p\n",
  39                                        __func__, __LINE__, i, node);
  40                                 trap();
  41                         }
  42                 }
  43
  44                 children += node->child[i]->children + 1;
  45
  46                 validate_subtree(node->child[i]);
  47         }
  48
  49         if (node->depth < 0) {
  50                 printf("%s:%d Tree statistics inconsistency detected! "
  51                        "Negative depth: %ld\n",
  52                        __func__, __LINE__, node->depth);
  53         }
  54
  55         if (node->children != children) {
  56                 printf("%s:%d Tree statistics inconsistency detected! "
  57                        "child count mismatch. Expected %ld, got %ld\n",
  58                        __func__, __LINE__, children, node->children);
  59                 trap();
  60         }
  61
  62         for (i = 0; i < 4 && node->children; i++) {
  63                 if (!node->child[i])
  64                         continue;
  65
  66                 if (node->depth == node->child[i]->depth + 1)
  67                         break;
  68
  69                 if (node->child[i]->depth > node->depth) {
  70                         printf("%s:%d Tree statistics inconsistency detected! "
  71                                "child depth mismatch %ld > %ld\n",
  72                                __func__, __LINE__, node->child[i]->depth,
  73                                node->depth);
  74                 }
  75         }
  76
  77         if (i == 4) {
  78                 printf("%s:%d Tree statistics inconsistency detected! "
  79                        "child depth mismatch.",
  80                        __func__, __LINE__);
  81                 trap();
  82         }
  83 }
  84
  85 static void validate_tree(const struct quadtree *node)
  86 {
  87         if (debug)
  88                 validate_subtree(quadtree_find_parent(node));
  89 }
  90
  91 /**
  92  * quadtree_add - add a node to a quadtree
  93  * @parent: parent node
  94  * @new: the new node to be added
  95  * @compare: pointer to a comparison function
  96  *
  97  * Add a node to a quadtree. The tree is kept in order, the new node
  98  * is placed in the end of appropriate branch. The compare function is
  99  * used to compare the new node against a branch in the tree. The
 100  * comparison function must have following return value depending on
 101  * the position of node a compared to the position of node b:
 102  *
 103  * 0: upper left
 104  * 1: upper right
 105  * 2: lower left
 106  * 3: lower right
 107  *
 108  * The case of nodes sharing identical coordinates is not taken into
 109  * account at all.
 110  */
 111
 112 struct quadtree *quadtree_add(struct quadtree *parent, struct quadtree *new,
 113                               struct quadtree_ops *ops)
 114 {
 115         int ret;
 116         if (parent == new)
 117                 trap();
 118
 119         validate_tree(parent);
 120
 121         ret = ops->compare(parent, new);
 122
 123         if (ret < 0 || ret >= 4) {
 124                 printf("Invalid comparison result of %d\n", ret);
 125                 return 0;
 126         }
 127
 128         if (parent->child[ret])
 129                 return quadtree_add(parent->child[ret], new, ops);
 130
 131         parent->child[ret] = new;
 132         new->parent = parent;
 133
 134         quadtree_recalculate_parent_stats(parent);
 135
 136         validate_tree(new);
 137
 138         return new;
 139 }
 140
 141 /*
 142  * _quadtree_reposition_reqursively - Move everything under and
 143  * including a given node under the new root node
 144  */
 145
 146 static void
 147 _quadtree_reposition_reqursively(struct quadtree *root,
 148                                  struct quadtree *node,
 149                                  struct quadtree_ops *ops)
 150 {
 151         int i;
 152
 153         validate_tree(node);
 154
 155         /* First remove all children, if any */
 156
 157         for (i = 0; i < 4; i++) {
 158                 if (!node->child[i])
 159                         continue;
 160
 161                 if (node->child[i] == node ||
 162                     node->child[i] == node->parent)
 163                         trap();
 164
 165                 _quadtree_reposition_reqursively(root, node->child[i], ops);
 166                 node->child[i] = 0;
 167         }
 168
 169         /* There are no children left, reset stats */
 170         node->depth = 0;
 171         node->children = 0;
 172
 173         /* Then remove this node under the new root. */
 174         quadtree_add(root, node, ops);
 175 }
 176
 177 /*
 178  * quadtree_del - Detach a node from the tree
 179  *
 180  * Return value: The new root node of the tree. If we are detaching
 181  * anything but the root node of the entire tree, the returned root
 182  * value will be the original root of the tree.
 183  */
 184 struct quadtree *quadtree_del(struct quadtree *node,
 185                               struct quadtree_ops *ops)
 186 {
 187         struct quadtree *parent = 0;
 188         int i;
 189
 190         /*
 191          * We are deleting the root node. This means we have to select
 192          * a new root node and reconstruct the entire tree under it
 193          * again.
 194          */
 195         if (!node->parent) {
 196                 for (i = 0; i < 4; i++) {
 197                         if (!node->child[i])
 198                                 continue;
 199
 200                         if (!parent) {
 201                                 parent = node->child[i];
 202                                 continue;
 203                         }
 204                         _quadtree_reposition_reqursively(parent,
 205                                                          node->child[i],
 206                                                          ops);
 207                         node->child[i] = 0;
 208                 }
 209
 210                 return parent;
 211         }
 212
 213         /*
 214          * We are not deleting the parent. Detach the node from the
 215          * parent abd relocate the children. The node will be then
 216          * detached from the tree.
 217          */
 218
 219         for (i = 0; i < 4; i++) {
 220                 if (node->parent->child[i] == node) {
 221                         node->parent->child[i] = 0;
 222                         break;
 223                 }
 224         }
 225         if (i == 4) {
 226                 printf("%s:%d Fatal! Tree inconsistency detected\n",
 227                        __func__, __LINE__);
 228                 trap();
 229         }
 230
 231         /* Fix parent stats */
 232         quadtree_recalculate_parent_stats(node->parent);
 233
 234         /*
 235          * The sub branch is now detached from the main tree. Continue
 236          * relocating the detached branch.
 237          */
 238
 239         for (i = 0; i < 4; i++) {
 240                 if (!node->child[i])
 241                         continue;
 242
 243                 _quadtree_reposition_reqursively(node->parent, node->child[i],
 244                                                  ops);
 245                 node->child[i] = 0;
 246         }
 247
 248         parent = quadtree_find_parent(node);
 249         node->parent = 0;
 250
 251         node->children = 0;
 252         node->depth = 0;
 253
 254         validate_tree(parent);
 255         return parent;
 256 }
 257
 258
 259 static int _walk_tree(struct quadtree *head, const struct quadtree_iterator *it)
 260 {
 261         int direction, count = 0;
 262
 263         direction = it->direction(head, (struct quadtree_iterator *)it);
 264
 265         if ((direction & QUADTREE_UPLEFT) && head->child[0])
 266                 count += _walk_tree(head->child[0], it);
 267
 268         if ((direction & QUADTREE_UPRIGHT) && head->child[1])
 269                 count += _walk_tree(head->child[1], it);
 270
 271         if ((direction & QUADTREE_DOWNLEFT) && head->child[2])
 272                 count += _walk_tree(head->child[2], it);
 273
 274         if ((direction & QUADTREE_DOWNRIGHT) && head->child[3])
 275                 count += _walk_tree(head->child[3], it);
 276
 277         if ((direction & QUADTREE_SELF) && it->callback) {
 278                 it->callback(head, (struct quadtree_iterator *)it);
 279                 count++;
 280         }
 281
 282         return count;
 283 }
 284
 285 int walk_quadtree(const struct quadtree_iterator *it)
 286 {
 287         return _walk_tree(it->head, it);
 288 }