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/*
* tileset.c:
* Interface to an individual tile set.
*
* Copyright (c) 2006 UK Citizens Online Democracy. All rights reserved.
* Email: chris@mysociety.org; WWW: http://www.mysociety.org/
*
*/
static const char rcsid[] = "$Id: tileset.c,v 1.5 2006-09-20 15:45:44 chris Exp $";
/*
* Tile sets are stored in directory trees which contain indices of tile
* locations to tile IDs, packed archives of tile images, and indices of where
* each tile image lives in the corresponding packed file. Tile IDs are SHA1
* digests of the tile contents, enabling efficient storage in the presence of
* repeated tiles.
*
* Note that this doesn't have attractive properties for locality of reference.
* That will need fixing if performance under the current scheme is not
* acceptable.
*/
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "cdb.h"
#include "tileset.h"
#include "util.h"
#define TILEID_LEN 20
struct tileset {
char *t_path, *t_pathbuf;
cdb t_tileid_idx;
/* Tile IDs are stored in the tile ID database in N-by-N square blocks,
* so that the tile ID for (X, Y) is obtained by getting the block for
* (X / N, Y / N) and looking up (X, Y) within it. The blocking factor is
* (hopefully!) chosen to be about a disk block in size. It is stored in
* the tile ID database. Rather than allocating a specific tile ID for a
* tile which is not present, each information block is preceded by a
* coverage bitmap. */
unsigned t_blocking;
bool t_first;
unsigned t_x, t_y;
cdb_datum t_block;
/* File pointer open on an image file and the name of the file it's open
* on. */
char *t_imgfile;
FILE *t_fpimg;
};
/* tileset_open PATH
* Open the tileset at PATH, returning a tileset object on success or NULL on
* failure. */
tileset tileset_open(const char *path) {
struct tileset *T, Tz = {0};
cdb_datum d = NULL;
char *s;
int i;
T = xmalloc(sizeof *T);
*T = Tz;
T->t_first = 1;
T->t_path = xstrdup(path);
T->t_pathbuf = xmalloc(strlen(path) + sizeof "/tiles/a/b/c/tiles.cdb");
/* Open the tile ID index. */
sprintf(T->t_pathbuf, "%s/index.cdb", T->t_path);
if (!(T->t_tileid_idx = cdb_open(T->t_pathbuf)))
goto fail;
/* get blocking factor */
if (!(d = cdb_get_string(T->t_tileid_idx, "blocking")))
goto fail;
s = (char*)d->cd_buf;
if (!(i = atoi(s)) || i < 0)
goto fail;
T->t_blocking = (unsigned)i;
cdb_datum_free(d);
return T;
fail:
tileset_close(T);
if (d) cdb_datum_free(d);
return NULL;
}
/* tileset_close T
* Free resources associated with T. */
void tileset_close(tileset T) {
if (!T) return;
cdb_close(T->t_tileid_idx);
xfree(T->t_path);
xfree(T->t_pathbuf);
xfree(T);
}
static size_t blockmap_bitmap_len(const unsigned blocking) {
return (blocking * blocking + 8) / 8;
}
static size_t blockmap_len(const unsigned blocking) {
size_t l;
/* Bitmap of null tiles. */
l = blockmap_bitmap_len(blocking);
/* Tile IDs themselves */
l += blocking * blocking * TILEID_LEN;
return l;
}
/* tileset_get_tileid T X Y ID
* Write into ID the tile ID of the tile at (X, Y) in T, returning true on
* success or false on failure. */
bool tileset_get_tileid(tileset T, const unsigned x, const unsigned y,
uint8_t *id) {
unsigned x2, y2, off, off0;
uint8_t *b;
if (T->t_first || T->t_x != x || T->t_y != y) {
/* Grab block from database. */
char buf[32];
T->t_first = 0;
if (T->t_block) cdb_datum_free(T->t_block);
sprintf(buf, "%u,%u", x / T->t_blocking, y / T->t_blocking);
if (!(T->t_block = cdb_get_string(T->t_tileid_idx, buf)))
return 0;
}
if (T->t_block->cd_len != blockmap_len(T->t_blocking))
return 0;
/* XXX also report bogus ID block */
b = (uint8_t*)T->t_block->cd_buf;
x2 = x % T->t_blocking;
y2 = y % T->t_blocking;
off = (x2 + y2 * T->t_blocking);
/* For a tile not present the corresponding bit in the bitmap is set. */
if (b[off >> 3] & (1 << (off & 7)))
return 0;
off0 = blockmap_bitmap_len(T->t_blocking);
memcpy(id, b + off0 + off * TILEID_LEN, TILEID_LEN);
return 1;
}
/* tileset_get_tile T ID LEN
* Retrieve the tile identified by ID, writing its length into *LEN and
* returning a malloced buffer containing its contents on success, or returning
* NULL on failure. */
void *tileset_get_tile(tileset T, const uint8_t *id, size_t *len) {
cdb idx = NULL;
cdb_datum d = NULL;
void *ret = NULL;
unsigned off;
FILE *fp = NULL;
sprintf(T->t_pathbuf, "%s/tiles/%x/%x/%x/tiles.cdb",
T->t_path, (unsigned)(id[0] >> 4),
(unsigned)(id[0] & 0xf), (unsigned)(id[1] >> 4));
if (!(idx = cdb_open(T->t_pathbuf)))
return NULL;
/* also maybe report bogus index */
if (!(d = cdb_get_buf(idx, id, TILEID_LEN)))
goto fail;
if (2 != sscanf((char*)d->cd_buf, "%x:%x", &off, len))
goto fail;
sprintf(T->t_pathbuf, "%s/tiles/%x/%x/%x/tiles",
T->t_path, (unsigned)(id[0] >> 4),
(unsigned)(id[0] & 0xf), (unsigned)(id[1] >> 4));
if (!(fp = fopen(T->t_pathbuf, "rb")))
goto fail;
else if (-1 == fseek(fp, off, SEEK_SET))
goto fail;
ret = xmalloc(*len);
if (*len != fread(ret, 1, *len, fp)) {
xfree(ret);
goto fail;
}
fail:
if (idx) cdb_close(idx);
if (d) cdb_datum_free(d);
if (fp) fclose(fp);
return ret;
}
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