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kdtree.c
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kdtree.c
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#include "kdtree.h"
#include <stdlib.h>
#include <assert.h>
#include <math.h>
#include <stdio.h>
#include <float.h>
void kdtree_initialize(KDTree * kdtree) {
kdtree->capacity = 0;
kdtree->count = 0;
kdtree->items = NULL;
kdtree->nodes = NULL;
}
void kdtree_set_capacity(KDTree * kdtree, size_t capacity) {
kdtree->nodes = realloc(kdtree->nodes, sizeof(KDTreeNode) * capacity);
assert(kdtree->nodes != NULL);
kdtree->items = realloc(kdtree->items, sizeof(KDTreeItem) * capacity);
assert(kdtree->items != NULL);
kdtree->capacity = capacity;
}
void kdtree_clear(KDTree * kdtree) {
kdtree->count = 0;
}
void kdtree_add(KDTree * kdtree, Vector position, void * ref) {
assert(kdtree->count < kdtree->capacity);
KDTreeItem * item = &kdtree->items[kdtree->count++];
item->position = position;
item->ref = ref;
}
static Vector load_item_position(const void * item_ptr) {
return ((const KDTreeItem *)item_ptr)->position;
}
static int compare_float(float a, float b) {
if (a < b) return -1;
if (a > b) return 1;
return 0;
}
static int compare_item_x(const void * a, const void * b) {
return compare_float(load_item_position(a).x, load_item_position(b).x);
}
static int compare_item_y(const void * a, const void * b) {
return compare_float(load_item_position(a).y, load_item_position(b).y);
}
static KDTreeNode * get_next_node(KDTree * kdtree, int * count) {
assert(*count < kdtree->count);
return &kdtree->nodes[(*count)++];
}
static KDTreeNode * build_recursive_node(KDTree * kdtree, KDTreeItem * items, size_t items_length, int depth, int * count) {
if (items_length == 0)
return NULL;
int (*compare_fn)(const void *, const void *) = depth%2 == 0 ? compare_item_x : compare_item_y;
qsort(items, items_length, sizeof(KDTreeItem), compare_fn);
KDTreeNode * node = get_next_node(kdtree, count);
size_t median_item_index = items_length / 2;
while (median_item_index > 0 && compare_fn(&items[median_item_index], &items[median_item_index-1]) == 0) {
median_item_index--;
}
size_t right_item_index = median_item_index + 1;
node->item = items[median_item_index];
node->left = build_recursive_node(kdtree, &items[0], median_item_index, depth+1, count);
node->right = build_recursive_node(kdtree, &items[right_item_index], items_length - right_item_index, depth+1, count);
return node;
}
void kdtree_build(KDTree * kdtree) {
if (kdtree->count == 0)
return;
int count = 0;
build_recursive_node(kdtree, kdtree->items, kdtree->count, 0, &count);
assert(count == kdtree->count);
}
typedef struct {
float distance;
KDTreeNode * node;
} KDTreeNodeDistance;
static KDTreeNodeDistance get_node_distance(KDTreeNode * node, Vector position) {
assert(node != NULL);
return (KDTreeNodeDistance){ vector_sq_distance(node->item.position, position), node };
}
static float get_position_on_axis(Vector vector, int depth) {
return depth%2 == 0 ? vector.x : vector.y;
}
static KDTreeNodeDistance get_better_node_distance(KDTreeNodeDistance left, KDTreeNodeDistance right, void * excluding_ref) {
return right.node->item.ref == excluding_ref || (left.distance < right.distance && left.node->item.ref != excluding_ref) ? left : right;
}
static KDTreeNodeDistance get_closer_node_distance(KDTreeNodeDistance current_nd, Vector position, void * excluding_ref, int depth) {
KDTreeNode * current_node = current_nd.node;
float current_position = get_position_on_axis(current_node->item.position, depth);
float target_position = get_position_on_axis(position, depth);
int position_comparison = target_position >= current_position;
KDTreeNodeDistance current_best_nd;
KDTreeNode * next_node = position_comparison ? current_node->right : current_node->left;
if (next_node == NULL)
current_best_nd = current_nd;
else {
KDTreeNodeDistance next_nd = get_node_distance(next_node, position);
KDTreeNodeDistance closest_nd = get_closer_node_distance(next_nd, position, excluding_ref, depth+1);
current_best_nd = get_better_node_distance(closest_nd, current_nd, excluding_ref);
}
KDTreeNode * other_node = position_comparison ? current_node->left : current_node->right;
if (other_node != NULL) {
float splitting_coord_diff = current_position - target_position;
if (splitting_coord_diff * splitting_coord_diff < current_best_nd.distance) {
KDTreeNodeDistance other_nd = get_node_distance(other_node, position);
KDTreeNodeDistance other_best_nd = get_closer_node_distance(other_nd, position, excluding_ref, depth+1);
current_best_nd = get_better_node_distance(other_best_nd, current_best_nd, excluding_ref);
}
}
return current_best_nd;
}
KDTreeFindResult kdtree_find_distance_excluding(KDTree * kdtree, Vector position, void * excluding_ref) {
if (!kdtree->count)
return (KDTreeFindResult){NULL, FLT_MAX};
KDTreeNode * current_node = &kdtree->nodes[0];
KDTreeNodeDistance nd = get_node_distance(current_node, position);
KDTreeNodeDistance result = get_closer_node_distance(nd, position, excluding_ref, 0);
return (KDTreeFindResult){ result.node->item.ref, result.distance };
}
KDTreeFindResult kdtree_find_distance(KDTree * kdtree, Vector position) {
return kdtree_find_distance_excluding(kdtree, position, NULL);
}
void * kdtree_find(KDTree * kdtree, Vector position) {
return kdtree_find_distance(kdtree, position).ref;
}
static void kdtree_debug_print_node(int depth, KDTreeNode * node, void * param, void (* print_fn)(void * ref, void * param)) {
if (node == NULL) {
return;
}
printf("%*s(%4.1f,%4.1f) ", depth * 2, "", node->item.position.x, node->item.position.y);
print_fn(node->item.ref, param);
printf("\n");
kdtree_debug_print_node(depth+1, node->left, param, print_fn);
kdtree_debug_print_node(depth+1, node->right, param, print_fn);
}
void kdtree_debug_print(KDTree * kdtree, void * param, void (* print_fn)(void * ref, void * param)) {
printf("KDTREE DEBUG PRINT\ncapacity: %zu\ncount: %zu\n", kdtree->capacity, kdtree->count);
kdtree_debug_print_node(0, &kdtree->nodes[0], param, print_fn);
}
void kdtree_deinitialize(KDTree * kdtree) {
free(kdtree->nodes);
kdtree->nodes = NULL;
free(kdtree->items);
kdtree->items = NULL;
kdtree->capacity = 0;
kdtree->count = 0;
}