OPEN->NextNode=Node; // make Open List point to first node
for (;;)
{ //从Open表中取得一个估价值最好的节点
BestNode=ReturnBestNode();
//如果该节点是目标节点就退出
if (BestNode->NodeNum == TileNumDest) // if we've found the end, break and fini
1000
sh
break;
//否则生成子节点
GenerateSuccessors(BestNode,sx,sy);
}
PATH = BestNode;
}
再看看生成子节点函数 GenerateSuccessors:
void AstarPathfinder::GenerateSuccessors(NODE *BestNode, int dx, int dy)
{
int x, y;
//哦!依次生成八个方向的子节点,简单!
// Upper-Left
if ( FreeTile(x=BestNode->x-TILESIZE, y=BestNode->y-TILESIZE) )
GenerateSucc(BestNode,x,y,dx,dy);
// Upper
if ( FreeTile(x=BestNode->x, y=BestNode->y-TILESIZE) )
GenerateSucc(BestNode,x,y,dx,dy);
// Upper-Right
if ( FreeTile(x=BestNode->x+TILESIZE, y=BestNode->y-TILESIZE) )
GenerateSucc(BestNode,x,y,dx,dy);
// Right
if ( FreeTile(x=BestNode->x+TILESIZE, y=BestNode->y) )
GenerateSucc(BestNode,x,y,dx,dy);
// Lower-Right
if ( FreeTile(x=BestNode->x+TILESIZE, y=BestNode->y+TILESIZE) )
GenerateSucc(BestNode,x,y,dx,dy);
// Lower
if ( FreeTile(x=BestNode->x, y=BestNode->y+TILESIZE) )
GenerateSucc(BestNode,x,y,dx,dy);
// Lower-Left
if ( FreeTile(x=BestNode->x-TILESIZE, y=BestNode->y+TILESIZE) )
GenerateSucc(BestNode,x,y,dx,dy);
// Left
if ( FreeTile(x=BestNode->x-TILESIZE, y=BestNode->y) )
GenerateSucc(BestNode,x,y,dx,dy);
}
看看最重要的函数GenerateSucc:
void AstarPathfinder::GenerateSucc(NODE *BestNode,int x, int y, int dx, int dy)
{
int g, TileNumS, c = 0;
NODE *Old, *Successor;
//计算子节点的 g 值
g = BestNode->g+1; // g(Successor)=g(BestNode)+cost of getting from BestNode to Successor
TileNumS = TileNum(x,y); // identification purposes
//子节点再Open表中吗?
if ( (Old=CheckOPEN(TileNumS)) != NULL ) // if equal to NULL then not in OPEN list, else it returns the Node in Old
{
//若在
for( c = 0; c <8; c++) if( BestNode->Child[c] == NULL ) // Add Old to the list of BestNode's Children (or Successors).
break;
BestNode->Child[c] = Old;
//比较Open表中的估价值和当前的估价值(只要比较g值就可以了)
if ( g g ) // if our new g value is Old's then reset Old's parent to point to BestNode { //当前的估价值小就更新Open表中的估价值 Old-Parent = BestNode;
Old->g = g;
Old->f = g + Old->h;
}
}
else //在Closed表中吗?
if ( (Old=CheckCLOSED(TileNumS)) != NULL ) // if equal to NULL then not in OPEN list, else it returns the Node in Old
{
//若在
for( c = 0; c<8; c++) if ( BestNode->Child[c] == NULL ) // Add Old to the list of BestNode's Children (or Successors).
break;
BestNode->Child[c] = Old;
//比较Closed表中的估价值和当前的估价值(只要比较g值就可以了)
if ( g g ) // if our new g value is Old's then reset Old's parent to point to BestNode { //当前的估价值小就更新Closed表中的估价值 Old-Parent = BestNode;
Old->g = g;
Old->f = g + Old->h;
//再依次更新Old的所有子节点的估价值
PropagateDown(Old); // Since we changed the g value of Old, we need
// to propagate this new value downwards, i.e.
// do a Depth-First traversal of the tree!
}
}
else//不在Open表中也不在Close表中
{
//生成新的节点
Successor = ( NODE* )calloc(1,sizeof( NODE ));
Successor->Parent = BestNode;
Successor->g = g;
Successor->h = (x-dx)*(x-dx) + (y-dy)*(y-dy); // should do sqrt(), but since we don't really
Successor->f = g+Successor->h; // care about the distance but just which branch looks
Successor->x = x; // better this should suffice. Anyayz it's faster.
Successor->y = y;
Successor->NodeNum = TileNumS;
//再插入Open表中,同时排序。
Insert(Successor); // Insert Successor on OPEN list wrt f
for( c =0; c <8; c++) if ( BestNo
457
de->Child[c] == NULL ) // Add Old to the list of BestNode's Children (or Successors).
break;
BestNode->Child[c] = Successor;
}
}
哈哈!A*算法我懂了!当然,我希望你有这样的感觉!不过我还要再说几句。仔细看看这个程 序,你会发现,这个程序和我前面说的伪程序有一些不同,在GenerateSucc函数中,当子节点 在Closed表中时,没有将子节点从Closed表中删除并放入Open表中。而是直接的重新的计算该 节点的所有子节点的估价值(用PropagateDown函数)。这样可以快一些!另当子节点在 Open 表和Closed表中时,重新的计算估价值后,没有重新的对Open表中的节点排序,我有些想不通, 为什么不排呢?:-(,会不会是一个小小的BUG。你知道告诉我好吗?
// 路径寻找主函数
int * findpath(void)
{
TREE root;
int i,j;
int * path;
memset(dis_map,0xff,map_h*map_w*sizeof(*dis_map)); //填充dis_map为0XFF,表示各点未曾经过
init_queue();
root=(TREE)malloc(sizeof(*root));
root->tile=tile_num(start_x,start_y);
root->h=0;
root->father=NULL;
enter_queue(root,judge(start_x,start_y));
for (;;) {
int x,y,child;
TREE p;
root=get_from_queue();
if (root==NULL) {
return NULL;
}
x=tile_x(root->tile);
y=tile_y(root->tile);
if (x==end_x && y==end_y) break; // 达到目的地成功返回
void printpath(int *path)
{
int i;
if(path==NULL) return ;
for (i=0;path[i]>=0;i++) {
gotoxy(tile_x(path[i])+1,tile_y(path[i])+1);
cprintf(".");
}
}
int readmap()
{
FILE *f;
int i,j;
f=fopen("map.dat","r");
assert(f);
fscanf(f,"%d,%d\n",&map_w,&map_h);
map=malloc(map_w*map_h+1);
assert(map);
for(i=0;i<map_h;i++)
fgets(map+tile_num(0,i),map_w+2,f);
fclose(f);
start_x=-1,end_x=-1;
for (i=0;i<map_h;i++)
for (j=0;j<map_w;j++) {
if (map[tile_num(j,i)]=='s') map[tile_num(j,i)]=' ',start_x=j,start_y=i;
if (map[tile_num(j,i)]=='e') map[tile_num(j,i)]=' ',end_x=j,end_y=i;
}
assert(start_x>=0 && end_x>=0);
dis_map=malloc(map_w*map_h*sizeof(*dis_map));
assert(dis_map);
return 0;
}
void showmap()
{
int i,j;
clrscr();
for (i=0;i<map_h;i++) {
gotoxy(1,i+1);
for (j=0;j<map_w;j++)
if (map[tile_num(j,i)]!=' ') cprintf("O");
else cprintf(" ");
}
gotoxy(start_x+1,start_y+1);
cprintf("s");
gotoxy(end_x+1,end_y+1);
cprintf("e");
}
int main()
{
int * path;
readmap();
showmap();
getch();
path=findpath();
printpath(path);
if(dis_map) free(dis_map);
if(path) free(path);
if(map) free(map);
getch();
return 0;
}
/*===============================================================================
地图文件:map.dat
79,24
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
o o o
o ooooooo o o
o o o oooooooooooooo o
o s o o o
oooooooooooooooooo o o
o oooooooooooooooooooooooooo oooooooo o
o oooooo o oooo o o o
o o o ooo ooo o
o oooo oooo o
o o oooooooooooooooooooooooooooooooooooooooooooooo
o oooooooooooooooooooooooo o
o o
o o
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo o
o o ooooooooooo
o o ooooooo o o
o o o o o
o ooooooooooo oooooooooo o o
o o e ooo o o
o ooooo o o o
o o oooooooooooooooooo oooooooo o
o o o
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
---------------------------------------------------------------------------------*/