337 lines
8.3 KiB
Markdown
337 lines
8.3 KiB
Markdown
# 6.绘制地图
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作为一个 RPG 游戏怎么能没有地图呢，<em>是时候绘制地图了！</em>
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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<strong>位置</strong>（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。
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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：
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- 起点（位置）。
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- 目标（位置）。
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- 叙述性描述，例如“森林小径”。
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- 在 <em>go</em> 命令中往哪里走的描述性标记
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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，<em>go</em>将改变玩家的位置。
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```c
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struct object {
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const char *description;
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const char *tag;
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struct object *location;
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struct object *destination;
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};
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```
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注意：
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- 显然，<em>目的地</em>在大多数其他对象（物品，NPC）中都没有使用
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- 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
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- 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<em>生成</em>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。
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思考题：为什么创建两个通道可以使我们的程序更加灵活？
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接下来我们将展开对象数组
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# object.h
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```c
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typedef struct object {
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const char *description;
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const char *tag;
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struct object *location;
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struct object *destination;
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} OBJECT;
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extern OBJECT objs[];
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#define field (objs + 0) //是不是觉得这个很熟悉
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#define cave (objs + 1)
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#define silver (objs + 2)
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#define gold (objs + 3)
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#define guard (objs + 4)
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#define player (objs + 5)
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#define intoCave (objs + 6)
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#define exitCave (objs + 7)
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#define endOfObjs (objs + 8)
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```
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# object.c
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```c
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#include <stdio.h>
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#include "object.h"
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OBJECT objs[] = {
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{"an open field" , "field" , NULL , NULL },
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{"a little cave" , "cave" , NULL , NULL },
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{"a silver coin" , "silver" , field, NULL },
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{"a gold coin" , "gold" , cave , NULL },
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{"a burly guard" , "guard" , field, NULL },
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{"yourself" , "yourself", field, NULL },
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{"a cave entrance", "entrance", field, cave },
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{"an exit" , "exit" , cave , field }
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};
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```
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我们将在 <em>misc.c</em> 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。
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# misc.h
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```c
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extern OBJECT *getPassage(OBJECT *from, OBJECT *to);
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extern OBJECT *actorHere(void);
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extern int listObjectsAtLocation(OBJECT *location);
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```
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# misc.c
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```c
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#include <stdio.h>
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#include "object.h"
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OBJECT *getPassage(OBJECT *from, OBJECT *to)
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{
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if (from != NULL && to != NULL)
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{
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OBJECT *obj;
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for (obj = objs; obj < endOfObjs; obj++) //寻找物品之间是否具有通道
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{
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if (obj->location == from && obj->destination == to)
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{
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return obj; //找到了
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}
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}
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}
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return NULL;//找不到
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}
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OBJECT *actorHere(void)
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{
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OBJECT *obj;
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for (obj = objs; obj < endOfObjs; obj++)
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{
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if (obj->location == player->location && obj == guard)
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{
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return obj;
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}
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}
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return NULL;
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}
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int listObjectsAtLocation(OBJECT *location)
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{
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int count = 0;
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OBJECT *obj;
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for (obj = objs; obj < endOfObjs; obj++)
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{
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if (obj != player && obj->location == location)
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{
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if (count++ == 0)
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{
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printf("You see:\n");
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}
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printf("%s\n", obj->description);
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}
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}
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return count;
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}
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```
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我们将在命令“go”的实现中使用新功能<em>getPassage</em>来确定是否存在可以将玩家带到所需位置的通道。
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# location.h
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```c
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extern void executeLook(const char *noun);
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extern void executeGo(const char *noun);
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```
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# location.c
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```c
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#include <stdio.h>
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#include <string.h>
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#include "object.h"
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#include "misc.h"
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#include "noun.h"
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void executeLook(const char *noun)
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{
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if (noun != NULL && strcmp(noun, "around") == 0)
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{
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printf("You are in %s.\n", player->location->description);
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listObjectsAtLocation(player->location);
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}
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else
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{
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printf("I don't understand what you want to see.\n");
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}
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}
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void executeGo(const char *noun)
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{
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OBJECT *obj = getVisible("where you want to go", noun);
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if (obj == NULL)
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{
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// already handled by getVisible
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}
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else if (getPassage(player->location, obj) != NULL)
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//go只会在有地方的时候才会运行起来
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{
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printf("OK.\n");
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player->location = obj;
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executeLook("around");
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}
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else if (obj->location != player->location)
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{
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printf("You don't see any %s here.\n", noun);
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}
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else if (obj->destination != NULL)
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{
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printf("OK.\n");
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player->location = obj->destination;
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executeLook("around");
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}
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else
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{
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printf("You can't get much closer than this.\n");
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}
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}
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```
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我们还将使用新功能<em>getPassage</em>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。
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# noun.h
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```c
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extern OBJECT *getVisible(const char *intention, const char *noun);
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extern OBJECT *getPossession(OBJECT *from, const char *verb, const char *noun);
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```
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# noun.c
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```c
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#include <stdbool.h>
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#include <stdio.h>
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#include <string.h>
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#include "object.h"
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#include "misc.h"
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static bool objectHasTag(OBJECT *obj, const char *noun)
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{
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return noun != NULL && *noun != '\0' && strcmp(noun, obj->tag) == 0;
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}
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static OBJECT *getObject(const char *noun)
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{
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OBJECT *obj, *res = NULL;
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for (obj = objs; obj < endOfObjs; obj++)
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{
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if (objectHasTag(obj, noun))
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{
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res = obj;
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}
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}
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return res;
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}
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OBJECT *getVisible(const char *intention, const char *noun)
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{
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OBJECT *obj = getObject(noun);
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if (obj == NULL)
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{
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printf("I don't understand %s.\n", intention);
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}
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else if (!(obj == player ||
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obj == player->location ||
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obj->location == player ||
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obj->location == player->location ||
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getPassage(player->location, obj) != NULL || //检查两个位置是否相邻
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(obj->location != NULL &&
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(obj->location->location == player ||
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obj->location->location == player->location))))
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{
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printf("You don't see any %s here.\n", noun);
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obj = NULL;
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}
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return obj;
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}
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OBJECT *getPossession(OBJECT *from, const char *verb, const char *noun)
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{
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OBJECT *obj = NULL;
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if (from == NULL)
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{
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printf("I don't understand who you want to %s.\n", verb);
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}
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else if ((obj = getObject(noun)) == NULL)
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{
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printf("I don't understand what you want to %s.\n", verb);
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}
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else if (obj == from)
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{
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printf("You should not be doing that to %s.\n", obj->description);
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obj = NULL;
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}
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else if (obj->location != from)
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{
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if (from == player)
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{
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printf("You are not holding any %s.\n", noun);
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}
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else
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{
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printf("There appears to be no %s you can get from %s.\n",
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noun, from->description);
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}
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obj = NULL;
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}
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return obj;
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}
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```
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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。
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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）
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```
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注：不用当成任务，自行实验即可
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```
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输出样例
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Welcome to Little Cave Adventure.
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You are in an open field.
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You see:
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a silver coin
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a burly guard
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a cave entrance
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--> go entrance
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OK.
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You are in a little cave.
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You see:
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a gold coin
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an exit
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--> go exit
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OK.
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You are in an open field.
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You see:
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a silver coin
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a burly guard
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a cave entrance
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--> go cave
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OK.
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You are in a little cave.
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You see:
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a gold coin
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an exit
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--> quit
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Bye!
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