bool TCOD_path_compute(TCOD_path_t p, int ox,int oy, int dx, int dy) {
TCOD_path_data_t *path=(TCOD_path_data_t *)p;
TCOD_IFNOT(p != NULL) return false;
path->ox=ox;
path->oy=oy;
path->dx=dx;
path->dy=dy;
TCOD_list_clear(path->path);
TCOD_list_clear(path->heap);
if ( ox == dx && oy == dy ) return true; /* trivial case */
/* check that origin and destination are inside the map */
TCOD_IFNOT((unsigned)ox < (unsigned)path->w && (unsigned)oy < (unsigned)path->h) return false;
TCOD_IFNOT((unsigned)dx < (unsigned)path->w && (unsigned)dy < (unsigned)path->h) return false;
/* initialize djikstra grids */
memset(path->grid,0,sizeof(float)*path->w*path->h);
memset(path->prev,NONE,sizeof(dir_t)*path->w*path->h);
path->heur[ ox + oy * path->w ] = 1.0f; /* anything != 0 */
TCOD_path_push_cell(path,ox,oy); /* put the origin cell as a bootstrap */
/* fill the djikstra grid until we reach dx,dy */
TCOD_path_set_cells(path);
if ( path->grid[dx + dy * path->w] == 0 ) return false; /* no path found */
/* there is a path. retrieve it */
do {
/* walk from destination to origin, using the 'prev' array */
int step=path->prev[ dx + dy * path->w ];
TCOD_list_push(path->path,(void *)(uintptr)step);
dx -= dirx[step];
dy -= diry[step];
} while ( dx != ox || dy != oy );
return true;
}
/* fill the grid, starting from the origin until we reach the destination */
static void TCOD_path_set_cells(TCOD_path_data_t *path, int cutoff) {
int stepstaken = 0;
while ( path->grid[path->dx + path->dy * path->w ] == 0 && ! TCOD_list_is_empty(path->heap) ) {
stepstaken++;
if (stepstaken > cutoff)
break;
int x,y,i,imax;
float distance;
TCOD_path_get_cell(path,&x,&y,&distance);
imax= ( path->diagonalCost == 0.0f ? 4 : 8) ;
for (i=0; i < imax; i++ ) {
/* convert i to dx,dy */
static int idirx[]={0,-1,1,0,-1,1,-1,1};
static int idiry[]={-1,0,0,1,-1,-1,1,1};
/* convert i to direction */
static dir_t prevdirs[] = {
NORTH, WEST, EAST, SOUTH, NORTH_WEST, NORTH_EAST,SOUTH_WEST,SOUTH_EAST
};
/* coordinate of the adjacent cell */
int cx=x+idirx[i];
int cy=y+idiry[i];
if ( cx >= 0 && cy >= 0 && cx < path->w && cy < path->h ) {
float walk_cost = TCOD_path_walk_cost(path,x,y,cx,cy);
if ( walk_cost > 0.0f ) {
/* in of the map and walkable */
float covered=distance + walk_cost * (i>=4 ? path->diagonalCost : 1.0f);
float previousCovered = path->grid[cx + cy * path->w ];
if ( previousCovered == 0 ) {
/* put a new cell in the heap */
int offset=cx + cy * path->w;
/* A* heuristic : remaining distance */
float remaining=(float)sqrt((cx-path->dx)*(cx-path->dx)+(cy-path->dy)*(cy-path->dy));
path->grid[ offset ] = covered;
path->heur[ offset ] = covered + remaining;
path->prev[ offset ] = prevdirs[i];
TCOD_path_push_cell(path,cx,cy);
} else if ( previousCovered > covered ) {
/* we found a better path to a cell already in the heap */
int offset=cx + cy * path->w;
path->grid[ offset ] = covered;
path->heur[ offset ] -= (previousCovered - covered); /* fix the A* score */
path->prev[ offset ] = prevdirs[i];
/* reorder the heap */
heap_reorder(path,offset);
}
}
}
}
}
}
