本篇是游戏中物件的定义与使用（7）的续篇。
Developing a Character ICS
Although
developing a character’s inventory system might make you cringe at first,
let me reassure you that it’s not much different from developing a map inventory
control system. You have the ability to add and remove items, but you don’t have
the
problem of dealing with the item coordinates on the map. Instead, a player’s ICS
keeps track of order, which means that players can rearrange the items as they
see fit.
Of course, this ordering is just a matter of arranging the linked list, but what
about
the items that can hold other items, such as backpacks? As long as you properly
categorize
the items as containers in the MIL Editor, you don’t need to worry.
Speaking of categorizing, the real magic happens when you want to equip or use
an item. Because each item is categorized, the character ICS can quickly
determine
what to do with the item in question. If the item is a weapon, the character ICS
can
ask to equip the item. If it’s a healing item, the player can consume it.
Beginning
to get the idea?
Finally, a
character ICS should allow the player to examine objects, which is the reason
for the mesh and image parameters in the MIL Editor. Whenever the game’s
player examines the object, the specific mesh or image is loaded and displayed.
Now, turn your attention to putting together a character ICS and example by
using
the ICS.
Defining the cCharICS Class
Interface:
//==================================================================================
// This structure contains char item information list.
//==================================================================================
typedef struct sCharItem
{
long item_index; // MIL item index
long quantity; // quantity of item (ie coins)
sCharItem* prev;
sCharItem* next;
long index; // map item index
long owner;
sCharItem* parent; // parent of a contained item
sCharItem()
{
memset(this, 0, sizeof(*this));
owner = -1;
}
~sCharItem()
{
delete next;
}
} *sCharItemPtr;
//==================================================================================
// This class encapsulate char inventory contrl system for character.
//==================================================================================
typedef class cCharIcs
{
private:
long m_num_items;
sCharItemPtr m_root_item;
private:
long get_next_long(FILE* fp);
float get_next_float(FILE* fp);
public:
cCharIcs();
~cCharIcs();
bool load(const char* filename);
bool save(const char* filename);
void free();
void add(long item_index, long quantity, sCharItemPtr owner_item);
void remove(sCharItemPtr item);
long get_num_items();
sCharItemPtr get_root_item();
sCharItemPtr get_item(long index);
void sort();
bool move_up(sCharItemPtr item);
bool move_down(sCharItemPtr item);
} *cCharIcsPtr;
Much like the cMapICS class,
the cCharICS class uses a special structure (sCharItem) that
tracks the MIL item numbers and quantity and maintains a linked list. Unlike the
sMapItem structure, however, sCharItem doesn’t care about the item’s
coordinates.
Implement:
//----------------------------------------------------------------------------
// Get numeric value from file.
//----------------------------------------------------------------------------
static void get_numeric_value(FILE* fp, char* buf, int size)
{
long pos;
int c;
// read until EOF or EOL or over buffer
for(pos = 0; (c = fgetc(fp)) != EOF && c != 0x0a && pos != size-1; pos++)
{
if((c >= '0' && c <= '9') || c == '.' || c == '-')
buf[pos] = c;
}
buf[pos] = 0;
}
//----------------------------------------------------------------------------
// Constructor, initialize member data.
//----------------------------------------------------------------------------
cCharIcs::cCharIcs()
{
memset(this, 0, sizeof(*this));
}
//----------------------------------------------------------------------------
// Destructor, free allocated resource.
//----------------------------------------------------------------------------
cCharIcs::~cCharIcs()
{
free();
}
//----------------------------------------------------------------------------
// free allocate resource.
//----------------------------------------------------------------------------
void cCharIcs::free()
{
m_num_items = 0;
delete m_root_item;
}
//----------------------------------------------------------------------------
// Load all char items from file.
//----------------------------------------------------------------------------
bool cCharIcs::load(const char* filename)
{
free(); // free a prior set
FILE* fp;
if((fp = fopen(filename, "rb")) == NULL)
return false;
sCharItemPtr item;
sCharItemPtr item_ptr = NULL;
// loop forever reading in items
while(1)
{
long item_index;
// get next item number (break if no more items, which is represented by a return value of -1).
if((item_index = get_next_long(fp)) == -1)
break;
// create a new map item and link it in
item = new sCharItem;
if(item_ptr == NULL)
m_root_item = item;
else
{
item->prev = item_ptr;
item_ptr->next = item;
}
item_ptr = item;
item->item_index = item_index;
item->quantity = get_next_long(fp);
item->owner = get_next_long(fp);
item->index = m_num_items++;
}
fclose(fp);
// match objects that belong to others
for(item_ptr = m_root_item; item_ptr != NULL; item_ptr = item_ptr->next)
{
// check if this item belongs to another
if(item_ptr->owner == -1)
continue;
// find matching parent item
for(item = m_root_item; item != NULL; item = item->next)
{
if(item_ptr->owner == item->index)
{
// a match, point to parent and stop scanning for parents.
item_ptr->parent = item;
break;
}
}
}
return true;
}
//----------------------------------------------------------------------------
// Save all char items to file.
//----------------------------------------------------------------------------
bool cCharIcs::save(const char* filename)
{
FILE* fp;
if((fp = fopen(filename, "wb")) == NULL)
return false;
long index = 0;
for(sCharItemPtr item = m_root_item; item != NULL; item = item->next)
{
item->index = index++;
// match child items to parents
if(item->parent)
item->owner = item->parent->index;
else
item->owner = -1;
fprintf(fp, "%lu\r\n%lu\r\n%ld\r\n", item->item_index, item->quantity, item->owner);
}
fclose(fp);
return true;
}
//----------------------------------------------------------------------------
// Add char item into list.
//----------------------------------------------------------------------------
void cCharIcs::add(long item_index, long quantity, sCharItemPtr owner_item)
{
sCharItemPtr item = new sCharItem;
// fill the item structure
item->item_index = item_index;
item->quantity = quantity;
item->parent = owner_item;
// insert into top of list
item->next = m_root_item;
if(m_root_item)
m_root_item->prev = item;
m_root_item = item;
}
//----------------------------------------------------------------------------
// Remove char item from list.
//----------------------------------------------------------------------------
void cCharIcs::remove(sCharItemPtr item)
{
sCharItemPtr next_item;
// remove child objects first
for(sCharItemPtr item_ptr = m_root_item; item_ptr != NULL; item_ptr = next_item)
{
next_item = item_ptr->next;
if(item_ptr->parent == item)
remove(item_ptr);
}
// remove from linked list and reset root if it's the current head of list.
if(item->prev)
item->prev->next = item->next;
else
m_root_item = item->next;
if(item->next)
item->next->prev = item->prev;
item->prev = item->next = NULL;
delete item;
}
//----------------------------------------------------------------------------
// Return number of map items.
//----------------------------------------------------------------------------
long cCharIcs::get_num_items()
{
return m_num_items;
}
//----------------------------------------------------------------------------
// Return root map item.
//----------------------------------------------------------------------------
sCharItemPtr cCharIcs::get_root_item()
{
return m_root_item;
}
//----------------------------------------------------------------------------
// Return map item with specified index.
//----------------------------------------------------------------------------
sCharItemPtr cCharIcs::get_item(long index)
{
sCharItemPtr item;
// loop until reached item index
for(item = m_root_item; item != NULL && index != 0; item = item->next)
index--;
return item;
}
//----------------------------------------------------------------------------
// Return long value from next line in file.
//----------------------------------------------------------------------------
long cCharIcs::get_next_long(FILE *fp)
{
char buf[1024];
get_numeric_value(fp, buf, sizeof(buf));
if(strlen(buf) == 0) // if there is no long value in file
return -1;
return atol(buf);
}
//----------------------------------------------------------------------------
// Return float value from next line in file.
//----------------------------------------------------------------------------
float cCharIcs::get_next_float(FILE *fp)
{
char buf[1024];
get_numeric_value(fp, buf, sizeof(buf));
return (float)atof(buf);
}
The cCharICS class, again, is much
like its cMapICS counterpart, except for the addition
of three more public functions— sort, move_up, and move_down. You use these
functions
to sort the character’s list of items. Their code is as follows:
//----------------------------------------------------------------------------
// Arrange char ics.
//----------------------------------------------------------------------------
void cCharIcs::sort()
{
// start at top of linked list and float each item up that has a lesser item_index,
// break if past bottom of list.
for(sCharItemPtr item = m_root_item; item != NULL; item = item->next)
{
// keep floating up while previous item has a lesser item_index value or
// until top of list has been rearched.
for(sCharItemPtr prev_item = item->prev; prev_item != NULL; prev_item = item->prev)
{
// break if no more to float up
if(prev_item->item_index <= item->item_index)
break;
// swap element
if(prev_item->prev)
prev_item->prev->next = item;
if((prev_item->next = item->next) != NULL)
item->next->prev = prev_item;
if((item->prev = prev_item->prev) == NULL)
m_root_item = item;
prev_item->prev = item;
item->next = prev_item;
}
}
}
//----------------------------------------------------------------------------
// Move one char item up.
//----------------------------------------------------------------------------
bool cCharIcs::move_up(sCharItemPtr item)
{
sCharItemPtr prev_item = item->prev;
if(prev_item == NULL)
return FALSE;
// swap item and item before it
if(prev_item->prev)
prev_item->prev->next = item;
if((prev_item->next = item->next) != NULL)
item->next->prev = prev_item;
if((item->prev = prev_item->prev) == NULL)
m_root_item = item;
prev_item->prev = item;
item->next = prev_item;
return TRUE;
}
//----------------------------------------------------------------------------
// Move one char item down.
//----------------------------------------------------------------------------
bool cCharIcs::move_down(sCharItemPtr item)
{
sCharItemPtr next_item = item->next;
if(next_item == NULL)
return FALSE;
// swap item and item after it
if((item->next = next_item->next) != NULL)
next_item->next->prev = item;
if((next_item->prev = item->prev) != NULL)
item->prev->next = next_item;
else
m_root_item = next_item;
next_item->next = item;
item->prev = next_item;
return TRUE;
}
Function 'sort' sorts the linked
list of items based on each item’s MIL item number, from
lowest to highest. If, on the other hand, you want to specifically order the
list yourself,
you can utilize the move_up and move_down functions, which take a pointer to a
sCharItem structure that is already contained in the list.
The move_up function moves the
specified sItem structure up in the linked list, and
move_down moves the specified structure down in the linked list. Figure 15.10
illustrates
the concept of using the Arrange, move_up, and move_down functions on a sample
linked list of items.
The rest of the functions in
cCharICS are identical in their functionality to the
cMapICS class, with the obvious exclusion of the item coordinates used when
adding
an item to the list. Even the storage format for character items is identical to
the
map item format, except for the coordinates.
Using the
cCharICS Class
To demonstrate the use of the
character ICS system, I created a demo application
named CharICS that maintains a list of items contained in the default.mil master
item list file. When you start the demo, you’ll see the
Inventory dialog box (shown in following snap). In the Inventory dialog box, the
list
box contains an imaginary character’s inventory, which you can manipulate by
using the buttons on the dialog box.
To use the CharICS demo, follow
these steps:
1. Click the Add Item button. The CharICS demo will add a random item from
the MIL to the inventory list.
2. Select an item from the list. Items are classified, so the Use and Equip
buttons
are enabled or disabled depending on which item you select from the
list. Clicking Equip has no effect; it comes into play later when you deal with
characters. Clicking Use, however, removes an item if it is flagged as USEONCE.
3. Click the Drop button to
drop an item (remove the item from the inventory
list) if it is flagged as CANDROP.
4. In order to arrange the items in the inventory, you can click an item and
then click either Sort Up or Sort Down. The selected item then moves up or
down in the list. To arrange the items by their item number in the list, click
Sort.
As a last, special treat, items that have matching meshes appear in the box on
the
right in the demo. The 3-D object spins around slowly so that you have a full
view
of all sides. Now, that’s cool!