# 6.绘制地图

作为一个 RPG 游戏怎么能没有地图呢，*是时候绘制地图了！*

绘制地图的最佳工具始终是：一支铅笔和一张纸。基本地图由**位置**（矩形）组成，由道路（箭头）连接。我们已经在第 3 章中创建了位置，现在我们将开始添加道路。

在虚拟世界中，“道路”可能是连接两个位置的任何东西：一条路，一扇门，沙漠中。基本上，一段经文具有以下属性：

- 起点（位置）。
- 目标（位置）。
- 叙述性描述，例如“森林小径”。
- 在 *go* 命令中往哪里走的描述性标记

考虑到这些属性，第 4 章中定义的结构对象就非常适合存储道路了。事实上，一个道路与一个项目或 NPC 并没有太大的不同，它作为“可见出口”存在于某个位置（该位置是起点）。它只是与某些命令的行为不同，特别是命令“go”：应用于道路，*go*将改变玩家的位置。

```c
struct object {
   const char    *description;
   const char    *tag;
   struct object *location;
   struct object *destination;
};
```

注意：

- 显然，*目的地*在大多数其他对象（物品，NPC）中都没有使用
- 通道总是朝一个方向运行;要双向连接两个位置，我们总是必须创建两个单独的通道。乍一看，这似乎很笨拙，但它确实给了我们很大的灵活性来完善命令“go”的行为
- 在大地图上，你可能会发现手动创建所有通道很乏味。所以，我强烈建议你使用自定义工具*生成*地图中重复性更强的部分。这里不会介绍这一点，但您可能会在第 9 章中找到一些灵感，我们将在其中讨论自动胜场。

::: warning 🤔 思考题：为什么创建两个通道可以使我们的程序更加灵活？
:::

接下来我们将展开对象数组

## object.h

```c
typedef struct object {
   const char    *description;
   const char    *tag;
   struct object *location;
   struct object *destination;
} OBJECT;

extern OBJECT objs[];

#define field      (objs + 0)   //是不是觉得这个很熟悉
#define cave       (objs + 1)
#define silver     (objs + 2)
#define gold       (objs + 3)
#define guard      (objs + 4)
#define player     (objs + 5)
#define intoCave   (objs + 6)
#define exitCave   (objs + 7)

#define endOfObjs  (objs + 8)
```

## object.c

```c
#include <stdio.h>
#include "object.h"

OBJECT objs[] = {
   {"an open field"  , "field"   , NULL , NULL  },
   {"a little cave"  , "cave"    , NULL , NULL  },
   {"a silver coin"  , "silver"  , field, NULL  },
   {"a gold coin"    , "gold"    , cave , NULL  },
   {"a burly guard"  , "guard"   , field, NULL  },
   {"yourself"       , "yourself", field, NULL  },
   {"a cave entrance", "entrance", field, cave  },
   {"an exit"        , "exit"    , cave , field }
};
```

我们将在 *misc.c* 中添加一个小的帮助函数，以确定两个给定位置之间是否存在通道。

## misc.h

```c
extern OBJECT *getPassage(OBJECT *from, OBJECT *to);
extern OBJECT *actorHere(void);
extern int listObjectsAtLocation(OBJECT *location);
```

## misc.c

```c
#include <stdio.h>
#include "object.h"

OBJECT *getPassage(OBJECT *from, OBJECT *to)
{
   if (from != NULL && to != NULL)
   {
      OBJECT *obj;
      for (obj = objs; obj < endOfObjs; obj++)   //寻找物品之间是否具有通道
      {
         if (obj->location == from && obj->destination == to)
         {
            return obj;  //找到了
         }
      }
   }
   return NULL;//找不到
}

OBJECT *actorHere(void)
{
   OBJECT *obj;
   for (obj = objs; obj < endOfObjs; obj++)
   {
      if (obj->location == player->location && obj == guard)
      {
         return obj;
      }
   }
   return NULL;
}

int listObjectsAtLocation(OBJECT *location)
{
   int count = 0;
   OBJECT *obj;
   for (obj = objs; obj < endOfObjs; obj++)
   {
      if (obj != player && obj->location == location)
      {
         if (count++ == 0)
         {
            printf("You see:\n");
         }
         printf("%s\n", obj->description);
      }
   }
   return count;
}
```

我们将在命令“go”的实现中使用新功能*getPassage*来确定是否存在可以将玩家带到所需位置的通道。

## location.h

```c
extern void executeLook(const char *noun);
extern void executeGo(const char *noun);
```

## location.c

```c
#include <stdio.h>
#include <string.h>
#include "object.h"
#include "misc.h"
#include "noun.h"

void executeLook(const char *noun)
{
   if (noun != NULL && strcmp(noun, "around") == 0)
   {
      printf("You are in %s.\n", player->location->description);
      listObjectsAtLocation(player->location);
   }
   else
   {
      printf("I don't understand what you want to see.\n");
   }
}

void executeGo(const char *noun)
{
   OBJECT *obj = getVisible("where you want to go", noun);
   if (obj == NULL)
   {
      // already handled by getVisible
   }
   else if (getPassage(player->location, obj) != NULL)
   //go 只会在有地方的时候才会运行起来
   {
      printf("OK.\n");
      player->location = obj;
      executeLook("around");
   }
   else if (obj->location != player->location)
   {
      printf("You don't see any %s here.\n", noun);
   }
   else if (obj->destination != NULL)
   {
      printf("OK.\n");
      player->location = obj->destination;
      executeLook("around");
   }
   else
   {
      printf("You can't get much closer than this.\n");
   }
}
```

我们还将使用新功能*getPassage*来确定从玩家站立的位置是否可以看到某个位置。未通过通道连接到当前位置的位置不被视为可见。

## noun.h

```c
extern OBJECT *getVisible(const char *intention, const char *noun);
extern OBJECT *getPossession(OBJECT *from, const char *verb, const char *noun);
```

## noun.c

```c
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include "object.h"
#include "misc.h"

static bool objectHasTag(OBJECT *obj, const char *noun)
{
   return noun != NULL && *noun != '\0' && strcmp(noun, obj->tag) == 0;
}

static OBJECT *getObject(const char *noun)
{
   OBJECT *obj, *res = NULL;
   for (obj = objs; obj < endOfObjs; obj++)
   {
      if (objectHasTag(obj, noun))
      {
         res = obj;
      }
   }
   return res;
}

OBJECT *getVisible(const char *intention, const char *noun)
{
   OBJECT *obj = getObject(noun);
   
   if (obj == NULL)
   {
      printf("I don't understand %s.\n", intention);
   }
   else if (!(obj == player ||
              obj == player->location ||
              obj->location == player ||
              obj->location == player->location ||
              getPassage(player->location, obj) != NULL ||   //检查两个位置是否相邻
              (obj->location != NULL &&
               (obj->location->location == player ||
                obj->location->location == player->location))))
   {
      printf("You don't see any %s here.\n", noun);
      obj = NULL;
   }
   return obj;
}

OBJECT *getPossession(OBJECT *from, const char *verb, const char *noun)
{
   OBJECT *obj = NULL;
   if (from == NULL)
   {
      printf("I don't understand who you want to %s.\n", verb);
   }
   else if ((obj = getObject(noun)) == NULL)
   {
      printf("I don't understand what you want to %s.\n", verb);
   }
   else if (obj == from)
   {
      printf("You should not be doing that to %s.\n", obj->description);
      obj = NULL;
   }
   else if (obj->location != from)
   {
      if (from == player)
      {
         printf("You are not holding any %s.\n", noun);
      }
      else
      {
         printf("There appears to be no %s you can get from %s.\n",
                noun, from->description);
      }
      obj = NULL;
   }
   return obj;
}
```

显然，此示例中的地图是微不足道的：只有两个位置，并且它们在两个方向上都连接在一起。第 12 章将增加第三个地点。

::: warning 🤔 思考题：
你能否绘制一张更精细的地图，并将其变成对象列表（位置和通道）

注：不用当成任务，自行实验即可

:::

输出样例

Welcome to Little Cave Adventure.
You are in an open field.
You see:
a silver coin
a burly guard
a cave entrance

--> go entrance
OK.
You are in a little cave.
You see:
a gold coin
an exit

--> go exit
OK.
You are in an open field.
You see:
a silver coin
a burly guard
a cave entrance

--> go cave
OK.
You are in a little cave.
You see:
a gold coin
an exit

--> quit

Bye!