Introduction to Building Nightmare Objects Nightmare IV Object Library written by Descartes of Borg 951204 If you are anything like I was when I became a creator for the first time, then your knowledge of computers consists of how to write a paper using WordPerfect and how to play the games you like to play. It probably seems like a long distance between that and actually writing programs to run on a computer. And the truth is, many years ago it was. Programming a computer is no longer really programming. It is more like playing with Legos. Whereas you used to feed into a computer step by step instructions on how the program is supposed to work, today instead you fit objects together like pieces of a puzzle and define their basic characteristics. The object library handles the rest. Of course, that begs the question, what is an object? It is easiest to understand the concept if you get out of the computer mindset. Just think about things like you do in every day life. Objects simply are things. Your house is an object, your car is an object, your floor is an object, your cat is an object, and you are an object. Programming for an LPMud is simply about defining what objects exist in the world. What distinguishes you from your cat? What distinguishes your cat from your neighbour's cat? Each object has two defining pieces, its attributes and its behaviour. An attribute is simply something that is true of the object, for example, your cat has green eyes, while your neighbours has blue. Things such as name, eye colour, fur length, tail length, mass, intelligence, etc. are all attributes. In building on muds, you will often hear attributes referred to as global variables. The other part of an object is its behaviour. In the real world, things happen to objects, and objects react. Your cat sees a bird. Seeing the bird causes the cat to salivate. The cat in turn hunts the bird. The chain of events really goes on and on with no identifiable beginning or end, except in the way you describe the event. For example, you could take the cat seeing the bird as being caused by the bird landing, which was caused by its migration south, which was caused by the change of seasons... The bottom line is that the world is full of objects which behave in response to events according to their attributes and built-in nature. Building objects on a mud therefore is about setting the attributes for specific objects and defining they way they react to certain events. Fortunately, the LPC language has built-in mechanism to make this easy. It is called inheritance. Going back to the cat example, let's say you were going to build a cat. You could go and rewrite every piece of behaviour common to your first cat and your neghbour's cat. If you were going to build ten cats, that would get tedious. LPC allows you to build a generic cat, then customize an instance of that generic class and make it your cat. The Nightmare Object Library is what its name implies, a library of objects that object-oriented terminology refers to as "abstract classes". An abstract class is a type of object you never see running around the mud. Instead, it is a building block used in the objects you see running around the mud. In other words, the object library builds the concept of cat, and you use this to build individual cats. Another analogy is that of the object library being like a Lego set. You take the pieces it gives you to build specific objects. In building an area, you know understand your task is to build the objects which make up that area. Building an object simply means using the abstract classes the object library gives you to create specific instances of those abstract classes. You do this by defining the specific attributes of the new objects, and defining new behaviours. You have probably heard me refer to the terms behaviour and event interchangeably. In philosophy, they are not interchangeable. A behaviour is a type of event which is defined as being caused by something that meant to cause the event. In other words, the cat chasing the bird is behaviour, while the cat seeing the bird is simply an event. Both are considered events. With respect to objects, you are really defining events, since some events are actually unintentional responses to other events. The Nightmare Object Library therefore refers to what you define in objects as events. Writing an event in LPC is nothing more that providing step by step instructions for what happens when a given event occurs. The LPC term for an event is a function (sometimes you will hear people refer to functions as methods). The Nightmare Object Library uses four types of events: #1 MudOS initiated events, sometimes called an "apply" The names of these events are all lower case. The most common apply is the create() event. It is caused by the creation of the object. #2 Attribute manipulation events These are the SetXXX() and GetXXX() events. They exist basically to allow other objects to find out about an object's attributes, or to do initial setup for an object's attributes. #3 Modal events These are the CanXXX() events. They get called often just prior to a behaviour type of an event. For example, I am trying to leave a room, so my leave behaviour asks the room if I can leave. This would be CanLeave() in the room. If CanLeave() says I can leave, then the leave event is triggered in the room. #4 True events A true event is identified by eventXXX(). These type of events are the meat of what is happening in the game. Any given true event is generally in turn triggered by some other true event. The chain generally can be traced as starting with a player or NPC command at some point. There are also two other types of functions which are not really events, but instead simple routines that perform complex operations, like the absolute_value() function. These functions belong to no particular object since they are not really events. Instead any object in the game may refer to them. You will hear them referred to sefuns (simul efuns) and efuns respectively. So, an object in the Nightmare Object Library consists of all of these events. That sounds like you have a lot to do? Not really. The object library itself defines almost all of the events needed for any particular object. Most often, you will be defining only one event for any object, the creation event (create()). The event create() is triggered by MudOS for every single object when it is first created. This is therefore the ideal place for defining what the attributes are for an object, so your create() generally ends up being a series of SetXXX() calls. In addition, if you add any attributes, you will want to give them values in create(). Take for example an NPC. Any NPC you build will have to have a name. Thus, when it gets created, you want to be sure to set its name. You do this through the SetKeyName() event. The documents in this directory primarily describe for you what SetXXX() functions exist in objects to allow you to define your own unique objects. Once you are feeling comfortable with building simple objects that only have create() behaviours, you can then start adding other behaviours to objects. For example, one type of behaviour you can add to some rooms is to respond to someone digging in the room. You thus define CanDig() and eventDig() events in addition to your create() event. In the event, whatever events you end up defining, they end up being nothing more than modifying attributes of the object in question, or causing events in other objects.
