Actions

[ LiB ]

Everything that happens in the physical part of the world is considered an action and this includes characters moving, attributes changing, items moving around, and people speaking.

A naive design would give each entity in the game specific calls for each event to look something like this:

 class Character {     void SawCharacterLeave( entityid p_char, entityid p_portal );     void SawCharacterEnter( entityid p_char, entityid p_portal );     ...     ...     ... }; 

Depending on the number of physical actions, this can end up making your codebase literally explode in size.

Instead, as mentioned previously, I use a special structure to represent actions, called the Action structure. (You can find this in /BetterMUD/Entities/Action.h.)

NOTE

There's a constructor that I didn't show in the previous code segment, but it simply takes parameters matching each one of the fields. It also uses default parameters for each of the arguments, so you don't have to use all the arguments all the time. You'll see this used in a bit.

 struct Action {     std::string actiontype;     entityid data1;     entityid data2;     entityid data3;     entityid data4;     std::string stringdata; }; 

An action contains six fields of data: two strings, and four entityid s. These fields contain enough data to represent the details of every physical action within the game.

For example, if you want to tell the game that character 1 entered the realm, you could create an action like this:

 Action a( "enterrealm", 1 ); 

Or when that character attempts to speak, you could create an action like this:

 Action b( "attemptsay", 1, 0, 0, 0, "Hello Game!!!" ); 

The constructor uses default parameter values, but if you want to use the data string, you need to pass in all parameters, even if they aren't used.

NOTE

I show you the meanings of all of the action parameters in a bit.

There are three major types of actions within the BetterMUD: attempted actions, query actions, and completed actions.

Attempted Actions

Attempted actions are basically requests to the game. You have a script attached to a character, and the script wants to move the character through a portal. The script then tells the game, "Hey, I want this character to go through a portal!" Some attempted actions such as trying to go through portals may fail; others, such as entering the realm, always work.

Attempted actions are always registered with the game module, which I show you in the next chapter.

Here is a listing of player- related attempted actions:

enterrealm a player is entering the realm

leaverealm a player is leaving the realm

announce a system-wide announcement is being made

chat a player wants to globally chat

attemptsay a player wants to speak in a room

vision a room-wide vision event is occurring

command a player wants to execute a command

Then we have some physical event requests:

attemptportalenter a character wants to enter a portal

attempttransport a character wants to teleport to another room without using a portal

transport a character is forced to teleport to another room, without asking permission

spawncharacter a new character wants to be spawned in a room

spawnitem a new item wants to be spawned at a location

destroycharacter a character is told to die

destroyitem an item is destroyed

attemptdropitem a character tries to drop an item

attemptgetitem a character tries to get an item

attemptgiveitem one character gives an item to another

There are also events that deal with the databases:

cleanup tells the item and character databases to clean up all their deleted instances

savedatabases tells the game to save all databases to disk

saveregion tells the game to save a particular region to disk

saveplayers tells the game to save the players (not all characters) to disk

savetimers tells the game to save all timers to disk

reloaditems tells the game to reload the item template database

reloadcharacters tells the game to reload the character template database

reloadregion tells the game to reload a particular region

reloadcommandscript tells the game to reload a command script by name

reloadlogicscript tells the game to reload a logic script by name

And then there are the attribute modifiers:

modifyattribute modify an attribute of an entity Actions

And finally, here are the other actions that don't fit into the other categories:

messagelogic send a generic text message to any logic module in the game

addlogic add a logic module to an entity

dellogic delete a logic module from an entity

do send a generic action event to an entity

Query Actions

Query actions are often supposed to return Booleans, and they govern things that can happen in the realm. For example, you may want to prohibit players of a specific type from picking up items of a specific type, or you may want items of a specific type to refuse to be picked up at all.

To figure out just what the heck can happen in the game, you need a bunch of query actions , which ask an item if an action is allowed.

Here is a list of query actions:

cansay can a character say something?

canleaveregion can a character leave a region?

canenterregion can a character enter a region?

canleaveroom can a character leave a room?

canenterportal can a character enter a portal?

cangetitem can a character get an item?

candropitem can a character drop an item?

canreceiveitem can a character receive an item given by another character?

query generic query that asks custom questions.

All these actions (except query , which I go over in much more detail in Chapter 15) should return a value of zero if the action is acceptable, or one if unacceptable. I know this sounds strange , since zero usually means "no" or "false," but it involves the workings of the action reporting system.

A collection of logic modules governs the actions of every character. If several scripts are attached to a character, the character asks each script if the action can be accomplished. Whenever an action returns non-zero , it is assumed that it is important to return the information to whomever called the script, so the game engine stops sending the action to each module, and just returns the value. Figure 14.1 shows the chaining system of the BetterMUD logic modules.

Figure 14.1. Modules are informed of actions until one of the modules returns a non-zero value.

graphic/14fig01.gif


So, if a character has a module (for example, a logic module for someone dedicated to a church ) that prevents him from picking up certain items (such as an evil relic), that script returns a value of 1 whenever the script prevents the character from getting an item. The script returns 0 if the action is allowed.

In a similar way, items and rooms are asked if they will allow characters to pick things up; I go over the specifics of all this logic in the next chapter.

Completed Actions

Now that you've seen what actions can be requested by scripts, you need to know about the other side of the equation. When you tell the game about an action, it tries to accomplish that action, and if it succeeds, it must tell every actor in the equation about what happened .

For example, if a script requests that a player enter a portal, the game tries to move the player, and a number of things must be done to accomplish that move. First, the player must ask the portal for permission to enter, and if he receives permission, the room and everyone in it is told that the player left the room and moved into a portal, the portal is told that the player entered, and then the new room and everyone in it is told that the player entered.

Here are the completed actions that entities are informed of:

enterrealm A character entered the realm.

leaverealm A character left the realm.

leave The game tells a character to leave the game state.

hangup The game tells a character to hang up.

enterregion A character entered a region.

enterroom A character entered a room.

leaveroom A character left a room.

leaveregion A character left a region.

enterportal A character entered a portal.

getitem A character got an item.

dropitem A character dropped an item.

giveitem A character gave an item to another character.

error An error occurred.

announce A system announcement was made.

say Someone said something.

spawnitem A new item was spawned.

spawncharacter A new character was spawned.

destroyitem An item was destroyed.

destroycharacter A character was destroyed.

messagelogic A message was sent to a logic module.

modifyattribute An attribute was modified.

The preceding lists constitute all of the actions possible within the entire game. Table 15.1 shows which entities are notified about which events.

Table 15.1. Entity Event Notifications

Event

Items

Characters

Rooms

Regions

Portals

enterrealm

no

yes

no

no

no

leaverealm

no

yes

no

no

no

leave

no

yes

no

no

no

hangup

no

yes

no

no

no

enterregion

no

yes

no

yes

no

enterroom

yes

yes

yes

no

no

leaveroom

yes

yes

yes

no

no

leaveregion

no

yes

no

yes

no

enterportal

no

yes

no

no

yes

getitem

yes

yes

yes

no

no

dropitem

yes

yes

yes

no

no

giveitem

yes

yes

no

no

no

error

no

yes

no

no

no

announce

no

yes

no

no

no

say

yes

yes

yes

no

no

spawnitem

yes

yes

yeso

no

no

spawncharacter

no

yes

yes

no

no

destroyitem

yes

yes

yes

yes

no

destroycharacter

no

yes

yes

yes

no

messagelogic

yes

yes

yes

yes

yes

modifyattributes

yes

yes

yes

yes

yes


Action Parameters

Tables 15.2, 15.3, and 15.4 list the parameters for each action event type. Most of the time you don't have to pass room numbers as arguments, since the logic modules can assume that the room in question is the room that currently contains the player.

Table 15.2. Attempted Action Parameters

Action

arg1

arg2

arg3

arg4

data

chat

player

-

-

-

text

announce

-

-

-

-

text

vision

room

-

-

-

text

enterrealm

player

-

-

-

-

leaverealm

player

-

-

-

-

attemptsay

character

-

-

-

text

command

character

-

-

-

text

attemptenterportal

character

portal

-

-

-

attempttransport

character

room

-

-

-

transport

character

room

-

-

-

attemptgetitem

character

item

quantity

-

-

attemptdropitem

character

item

quantity

-

-

attemptgiveitem

character

character

item

quantity

-

spawnitem

template

room/person

isroom/person?

quantity

-

spawncharacter

template

room

-

-

-

destroyitem

item

quantity

-

-

-

destroycharacter

character

-

-

-

-

cleanup

-

-

-

-

-

savedatabases

-

-

-

-

-

saveregion

region

-

-

-

-

saveplayers

-

-

-

-

-

savetimers

-

-

-

-

-

reloaditems

-

-

-

-

file

reloadcharacters

-

-

-

-

file

reloadregion

-

-

-

-

name

reloadcommandscript

-

-

-

-

name

reloadlogicscript

-

-

-

-

name

modifyattribute

entity type

entityid

value

-

name

messagelogic

entity type

entityid

-

-

name

addlogic

entity type

entityid

-

-

logic

dellogic

entity type

entityid

-

-

logic

do

entity type

entityid

-

-

text


Table 15.3. Query Action Parameters

Action

arg1

arg2

arg3

arg4

data

cansay

character

-

-

-

text

canleaveregion

character

region

-

-

-

canenterregion

character

region

-

-

-

canleaveroom

character

room

-

-

-

canenterroom

character

room

-

-

-

canenterportal

character

portal

-

-

-

cangetitem

character

item

quantity

-

-

candropitem

character

item

quantity

-

-

canreceiveitem

giver

receiver

item

quantity

query

optional

optional

optional

optional

optional


Table 15.4. Happened Action Parameters

Action

arg1

arg2

arg3

arg4

data

enterrealm

player

-

-

-

-

leaverealm

player

-

-

-

leave

-

-

-

-

-

hangup

-

-

-

-

-

enterregion

character

region

-

-

-

enterroom

character

portal

-

-

-

leaveroom

character

portal

-

-

-

leaveregion

character

region

-

-

-

enterportal

character

portal

-

-

-

getitem

character

item

-

-

-

dropitem

character

item

-

-

-

giveitem

character

recipient

item

-

error

text

announce

-

-

-

-

text

say

character

-

-

-

text

spawnitem

item

-

-

-

-

spawncharacter

character

-

-

-

-

destroyitem

item

-

-

-

-

destroycharacter

character

-

-

-

-

messagelogic

entity type

entityid

-

-

name

modifyattribute

entity type

entityid

value

-

name


A few of the actions are "routable" actions, in which the action is routed to a specific entity in the game. These actions have an entity type and an entity ID that determine where they go. Here is a listing of the entity types:

0character

1item

2room

3portal

4region

So if you wanted to set attribute foo of item number 24 to the value 80, then you would construct an action like this:

 Action a( "modifyattribute", 1, 24, 80, 0, "foo" ); 

[ LiB ]


MUD Game Programming
MUD Game Programming (Premier Press Game Development)
ISBN: 1592000908
EAN: 2147483647
Year: 2003
Pages: 147
Authors: Ron Penton

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