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#include <math.h>
#include <stddef.h>
#include <stdlib.h>
#include "util.h"
#include "geometry.h"
bool quad_contains_point(struct quad_region_t region,
struct point_t pt)
{
if (region.center.x - region.half_dim > pt.x ||
region.center.x + region.half_dim <= pt.x)
return false;
if (region.center.y - region.half_dim > pt.y ||
region.center.y + region.half_dim <= pt.y)
return false;
return true;
}
struct quadtree_node_t quadtree_new_node(struct point_t center,
double half_dim)
{
struct quadtree_node_t node;
node.region = (struct quad_region_t) { center, half_dim };
node.id = -1;
node.nw = NULL;
node.ne = NULL;
node.sw = NULL;
node.se = NULL;
return node;
}
void quadtree_subdivide(struct quadtree_node_t *node,
struct point_t *points)
{
node->nw = malloc(sizeof(struct quadtree_node_t));
node->ne = malloc(sizeof(struct quadtree_node_t));
node->sw = malloc(sizeof(struct quadtree_node_t));
node->se = malloc(sizeof(struct quadtree_node_t));
struct point_t center = node->region.center;
double quarter_dim = node->region.half_dim / 2;
struct point_t c_nw =
{ center.x - quarter_dim, center.y - quarter_dim };
*(node->nw) = quadtree_new_node(c_nw, quarter_dim);
struct point_t c_ne =
{ center.x + quarter_dim, center.y - quarter_dim };
*(node->ne) = quadtree_new_node(c_ne, quarter_dim);
struct point_t c_sw =
{ center.x - quarter_dim, center.y + quarter_dim };
*(node->sw) = quadtree_new_node(c_sw, quarter_dim);
struct point_t c_se =
{ center.x + quarter_dim, center.y + quarter_dim };
*(node->se) = quadtree_new_node(c_se, quarter_dim);
if (node->id != -1) {
/* move point to a child */
if (quad_contains_point(node->nw->region,
points[node->id]))
node->nw->id = node->id;
else if (quad_contains_point(node->ne->region,
points[node->id]))
node->ne->id = node->id;
else if (quad_contains_point(node->sw->region,
points[node->id]))
node->sw->id = node->id;
else
node->se->id = node->id;
node->id = -1;
}
}
bool quadtree_insert(struct quadtree_node_t *node,
struct point_t *points, int id)
{
if (!quad_contains_point(node->region, points[id]))
return false;
if (node->id == -1 && node->nw == NULL) {
node->id = id;
return true;
}
if (node->nw == NULL)
quadtree_subdivide(node, points);
if (quadtree_insert(node->nw, points, id)) return true;
if (quadtree_insert(node->ne, points, id)) return true;
if (quadtree_insert(node->sw, points, id)) return true;
if (quadtree_insert(node->se, points, id)) return true;
return false;
}
static int get_points_in_region(struct quadtree_node_t *node,
int* buffer)
{
if (node->id != -1) {
*buffer = node->id;
return 1;
}
if (node->nw != NULL) {
int n_points = 0;
n_points += get_points_in_region(node->nw, buffer + n_points);
n_points += get_points_in_region(node->ne, buffer + n_points);
n_points += get_points_in_region(node->sw, buffer + n_points);
n_points += get_points_in_region(node->se, buffer + n_points);
return n_points;
}
return 0;
}
int quadtree_get_closest(struct quadtree_node_t *node,
struct point_t *points,
struct point_t pt)
{
if (!quad_contains_point(node->region, pt))
return -1;
if (node->id != -1)
return node->id;
int closest;
if (node->nw != NULL) {
if ((closest = quadtree_get_closest(node->nw, points, pt)) != -1)
return closest;
if ((closest = quadtree_get_closest(node->ne, points, pt)) != -1)
return closest;
if ((closest = quadtree_get_closest(node->sw, points, pt)) != -1)
return closest;
if ((closest = quadtree_get_closest(node->se, points, pt)) != -1)
return closest;
/* closest point is in a subregion, but not the *same*
* subregion as the point itself, so we need to check against
* all points contained within the region
*/
int buffer[1000];
int n_points = get_points_in_region(node, buffer);
double dist = 1e9;
for (int i=0; i<n_points; i++) {
int id = buffer[i];
double d = distance(points[id], pt);
if (d < dist) {
closest = id;
dist = d;
}
}
return closest;
}
return -1;
}
void quadtree_free(struct quadtree_node_t *node)
{
if (node->nw != NULL) {
quadtree_free(node->nw);
quadtree_free(node->ne);
quadtree_free(node->sw);
quadtree_free(node->se);
}
free(node);
}
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