I'm currently working on a game. There will be quite a few different AI's, one for every enemy.
How do I go about implementing this? Do I make a base class, from which I derive a class for every single type of AI? Do I just make one big class, with all AI's in a select case? Maybe something else?
I'm doing this in Unity3d with C#.
Thanks!
Well I guess it depends,
There a plenty of ways of doing this.
1) Classical OOP, you can make a detailed class structure deriving from AI interface, and then work your class hierarchy from there.
2) You could use component oriented design, then create an AI component, which can be initialized and further expanded using different smaller components.
3) You can go the scripting route, scripting outside of your "Engine" your AI logic, this is nice because it offers separation between the core engine functionality and your particular game Logic.
In my opinion it certainly depends on your particular needs, I often Mix 1 && 3, but I guess you could go with 1 || 2 || 3, they are not totally exclusive.
I think another thing you should have in mind is your character control system and how you have implemented that, the character control system will have a direct impact in how you will implement your AI system architecture.
Good luck :)
Maybe design pattern "Strategy pattern" fits your needs. See wiki page.
It forces you to use similar interface for every AI.
It allows you to change AI algorithm of an enemy object at runtime.
A safe way to begin designing something like this is to create a unit AI interface, then place each AI into a separate class implementing it. Common functionality could be placed into helper classes.
In regards to object hierarchies, game AI should follow SOLID principles, as everything else.
Related
I'd like to write an application, which would imitate a player in an online game.
About the game: it is a strategy, where you can:
train your army (you have to have enough resources, then click on a unit, click train)
build buildings (mines, armories, houses,...)
attack enemies (select a unit, select an enemy, click attack)
transport resources between buildings
make researches (economics, military, technologic,...)
This is a simplified list and is just an example. Main thing is, that you have to do a lot of clicking, if you want to advance...
I allready have the 'navigational' part of the application (I used Watin library - http://watin.sourceforge.net/). That means, that I can use high level objects and manipulate them, for example:
Soldiers soldiers = Navigator.GetAllSoldiers();
soldiers.Move(someLocation);
Now I'd like to take the next step - write a kind of AI, which would simulate my gaming style. For this I have two ideas (and I don't like either of them):
login to the game and then follow a bunch of if statements in a loop (check if someone is attacking me, check if I can build something, check if I can attack somebody, loop)
design a kind of scripting language and write a compiler for it. This way I could write simple scripts and run them (Login(); CheckForAnAttack(); BuildSomething(); ...)
Any other ideas?
PS: some might take this as cheating and it probably is, but I look on this as a learning project and it will never be published or reselled.
A bunch of if statements is the best option if the strategy is not too complicated. However, this solution does not scale very well.
Making a scripting language (or, domain specific language as one would call that nowadays) does not buy you much. You are not going to have other people create AI agents are you? You can better use your programming language for that.
If the strategy gets more involved, you may want to look at Bayesian Belief Networks or Decision Graphs. These are good at looking for the best action in an uncertain environment in a structured and explicit way. If you google on these terms you'll find plenty of information and libraries to use.
Sounds like you want a finite state machine. I've used them to various degrees of success in coding bots. Depending on the game you're botting you could be better off coding an AI that learns, but it sounds like yours is simple enough not to need that complexity.
Don't make a new language, just make a library of functions you can call from your state machine.
Most strategy game AIs use a "hierarchical" approach, much in the same way you've already described: define relatively separate domains of action (i.e. deciding what to research is mostly independent from pathfinding), and then create an AI layer to handle just that domain. Then have a "top-level" AI layer that directs the intermediate layers to perform tasks.
How each of those intermediate layers work (and how your "general" layer works) can each determined separately. You might come up with something rather rigid and straightforward for the "What To Research" layer (based on your preferences), but you may need a more complicated approach for the "General" layer (which is likely directing and responding to inputs of the other layers).
Do you have the sourcecode behind the game? If not, it's going to be kind of hard tracing the positions of each CPU you're (your computer in your case) is battling against. You'll have to develop some sort of plugin that can do it because from the sound of it, you're dealing with some sort of RTS of some sort; That requires the evaluation of a lot of different position scenarios between a lot of different CPUs.
If you want to simulate your movements, you could trace your mouse using some WinAPI quite easily. You can also record your screen as you play (which probably won't help much, but might be of assistance if you're determined enough.).
To be brutally honest, what you're trying to do is damn near impossible for the type of game you're playing with. You didn't seem to think this through yet. Programming is a useful skill, but it's not magic.
Check out some stuff (if you can find any) on MIT Battlecode. It might be up your alley in terms of programming for this sort of thing.
First of all I must point out that this project(which only serves educational purposes), is too large for a single person to complete within a reasonable amount of time. But if you want the AI to imitate your personal playing style, another alternative that comes to mind are neural networks: You play the game a lot(really a lot) and record all moves you make and feed that data to such a network, and if all goes well, the AI should play roughly the same as you do. But I'm afraid this is just a third idea you won't like, because it would take a tremendeous amount of time to get it perfect.
I've been studying hierachial reinforcement learning problems, and while a lot of papers propose interesting ways for learning a policy, they all seem to assume they know in advance a graph structure describing the actions in the domain. For example, The MAXQ Method for Hierarchial Reinforcement Learning by Dietterich describes a complex graph of actions and sub-tasks for a simple Taxi domain, but not how this graph was discovered. How would you learn the hierarchy of this graph, and not just the policy?
In Dietterich's MAXQ, the graph is constructed manually. It's considered to be a task for the system designer, in the same way that coming up with a representation space and reward functions are.
Depending on what you're trying to achieve, you might want to automatically decompose the state space, learn relevant features, or transfer experience from simple tasks to more complex ones.
I'd suggest you just start reading papers that refer to the MAXQ one you linked to. Without knowing what exactly what you want to achieve, I can't be very prescriptive (and I'm not really on top of all the current RL research), but you might find relevant ideas in the work of Luo, Bell & McCollum or the papers by Madden & Howley.
This paper describes one approach that is a good starting point:
N. Mehta, S. Ray, P. Tadepalli, and T. Dietterich. Automatic Discovery and Transfer of MAXQ Hierarchies. In International Conference on Machine Learning, 2008.
http://web.engr.oregonstate.edu/~mehtane/papers/hi-mat.pdf
Say there is this agent out there moving about doing things. You don't know its internal goals (task graph). How do you infer its goals?
In way way, this is impossible. Just as it is impossible for me to know what goal you had mind when you put that box down: maybe you were tired, maybe you saw a killer bee, maybe you had to pee....
You are trying to model an agent's internal goal structure. In order to do that you need some sort of guidance as to what are the set of possible goals and how these are represented by actions. In the research literature this problem has been studied under the terms "plan recognition" and also with the use of POMDP (partially observable markov decision process), but both of these techniques assume you do know something about the other agent's goals.
If you don't know anything about its goals, all you can do is either infer one of the above models (This is what we humans do. I assume others have the same goals I do. I never think, "Oh, he dropped his laptop, he must be ready to lay an egg" cse, he's a human.) or model it as a black box: a simple state-to-actions function then add internal states as needed (hmmmm, someone must have written a paper on this, but I don't know who).
Can anyone please give me any example of situation in a database-driven application where I should use Flyweight pattern?
How can I know that, I should use flyweight pattern at a point in my application?
I have learned flyweight pattern. But not able to understand an appropriate place in my database-driven business applications to use it.
Except for a very specialized database application, the Flyweight might be used by your application, but probably not for any class that represents an entity which is persisted in your database. Flyweight is used when there otherwise might be a need for so many instantiations of a class that if you instantiated one every discrete time you needed it performance would suffer. So instead, you instantiate a much smaller number of them and reuse them for each required instance by just changing data values for each use. This would be useful in a situation where, for example, you might have to instantiate thousands of such classes each second, which is generally not the case for entities persisted in a database.
You should apply any pattern when it naturally suggests itself as a solution to a concrete problem - not go looking for places in your application where you can apply a given pattern.
Flyweight's purpose is to address memory issues, so it only makes sense to apply it after you have profiled an application and determined that you have a ton of identical instances.
Colors and Brushes from the Base Class Library come to mind as examples.
Since a very important part of Flyweight is that the shared implementation is immutable, good candidates in a data-driven application would be what Domain-Driven Design refers to as Value Objects - but it only becomes relevant if you have a lot of identical values.
[Not a DB guy so this is my best guess]
The real bonus to the flyweight pattern is that you can reuse data if you need to; Another example is word processing where ideally you would have an object per "character" in your document, but that wuld eat up way too much memory so the flyweight memory lets you only store one of each unique value that you need.
A second (and perhaps simplest) way to look at it is like object pooling, only you're pooling on a "per-field" level as opposed to a "per-object" level.
In fact, now that i think about it, it's not unlike using a (comparatively small) chunk of memory in c(++) so store some raw data which you do pointer manipulation to get stuff out of.
[See this wikpedia article].
What are the pros and cons of having multiple inheritance?
And why don't we have multiple inheritance in C#?
UPDATE
Ok so it is currently avoided because of the issue with clashes resolving which parent method is being called etc. Surely this is a problem for the programmer to resolve. Or maybe this could be resolve simularly as SQL where there is a conflict more information is required i.e. ID might need to become Sales.ID to resolve a conflict in the query.
Here is a good discussion on the pitfalls of multiple inheritance:
Why should I avoid multiple inheritance in C++?
Here is a discussion from the C# team on why they decided not to allow multiple inheritance:
http://blogs.msdn.com/csharpfaq/archive/2004/03/07/85562.aspx
http://dotnetjunkies.com/WebLog/unknownreference/archive/2003/09/04/1401.aspx
It's just another tool in the toolbox. Sometimes, it is exactly the right tool. If it is, having to find a workaround because the language actually prohibits it is a pain and leads to good opportunities to screw it up.
Pros and cons can only be found for a concrete case. I guess that it's quite rare to actually fit a problem, but who are the language designers to decide how I am to tackle a specific problem?
I will give a pro here based on a C++ report-writer I've been converting to REALbasic (which has interfaces but only single-inheritance).
Multiple inheritance makes it easier to compose classes from small mixin base classes that implement functionality and have properties to remember state. When done right, you can get a lot of reuse of small code without having to copy-and-paste similar code to implement interfaces.
Fortunately, REALbasic has extends methods which are like the extension methods recently added to C# in C# 3.0. These help a bit with the problem, especially as they can be applied to arrays. I still ended up with some class hierarchies being deeper as a result of folding in what were previously multiply-inherited classes.
The main con is that if two classes have a method with the same name, the new subclass doesn't know which one to call.
In C# you can do a form of multiple inheritance by including instances of each parent object within the child.
class MyClass
{
private class1 : Class1;
private class2: Class2;
public MyClass
{
class1 = new Class1;
class2 = new Class2;
}
// Then, expose whatever functionality you need to from there.
}
When you inherit from something you are asserting that your class is of that (base) type in every way except that you may implement something slightly differently or add something to it, its actually extremely rare that your class is 2 things at once. Usually it just has behavour common to 2 or more things, and a better way to describe that generally is to have your class implement multiple interfaces. (or possibly encapsulation, depending on your circumstances)
It's one of those help-me-to-not-shoot-myself-in-the-foot quirks, much like in Java.
Although it is nice to extend fields and methods from multiple sources (imagine a Modern Mobile Phone, which inherits from MP3 Players, Cameras, Sat-Navs, and the humble Old School Mobile Phone), clashes cannot be resolved by the compiler alone.
I used to have one class for one file. For example car.cs has the class car. But as I program more classes, I would like to add them to the same file. For example car.cs has the class car and the door class, etc.
My question is good for Java, C#, PHP or any other programming language. Should I try not having multiple classes in the same file or is it ok?
I think you should try to keep your code to 1 class per file.
I suggest this because it will be easier to find your class later. Also, it will work better with your source control system (if a file changes, then you know that a particular class has changed).
The only time I think it's correct to use more than one class per file is when you are using internal classes... but internal classes are inside another class, and thus can be left inside the same file. The inner classes roles are strongly related to the outer classes, so placing them in the same file is fine.
In Java, one public class per file is the way the language works. A group of Java files can be collected into a package.
In Python, however, files are "modules", and typically have a number of closely related classes. A Python package is a directory, just like a Java package.
This gives Python an extra level of grouping between class and package.
There is no one right answer that is language-agnostic. It varies with the language.
One class per file is a good rule, but it's appropriate to make some exceptions. For instance, if I'm working in a project where most classes have associated collection types, often I'll keep the class and its collection in the same file, e.g.:
public class Customer { /* whatever */ }
public class CustomerCollection : List<Customer> { /* whatever */ }
The best rule of thumb is to keep one class per file except when that starts to make things harder rather than easier. Since Visual Studio's Find in Files is so effective, you probably won't have to spend much time looking through the file structure anyway.
No I don't think it's an entirely bad practice. What I mean by that is in general it's best to have a separate file per class, but there are definitely good exception cases where it's better to have a bunch of classes in one file. A good example of this is a group of Exception classes, if you have a few dozen of these for a given group does it really make sense to have separate a separate file for each two liner class? I would argue not. In this case having a group of exceptions in one class is much less cumbersome and simple IMHO.
I've found that whenever I try to combine multiple types into a single file, I always end going back and separating them simply because it makes them easier to find. Whenever I combine, there is always ultimately a moment where I'm trying to figure out wtf I defined type x.
So now, my personal rule is that each individual type (except maybe for child classes, by which a mean a class inside a class, not an inherited class) gets its own file.
Since your IDE Provides you with a "Navigate to" functionality and you have some control over namespacing within your classes then the below benefits of having multiple classes within the same file are quite worth it for me.
Parent - Child Classes
In many cases i find it quite helpful to have Inherited classes within their Base Class file.
It's quite easy then to see which properties and methods your child class inherits and the file provides a faster overview of the overall functionality.
Public: Small - Helper - DTO Classes
When you need several plain and small classes for a specific functionality i find it quite redundant to have a file with all the references and includes for just a 4-8 Liner class.....
Code navigation is also easier just scrolling over one file instead of switching between 10 files...Its also easier to refactor when you have to edit just one reference instead of 10.....
Overall breaking the Iron rule of 1 class per file provides some extra freedom to organize your code.
What happens then, really depends on your IDE, Language,Team Communication and Organizing Skills.
But if you want that freedom why sacrifice it for an iron rule?
The rule I always go by is to have one main class in a file with the same name. I may or may not include helper classes in that file depending on how tightly they're coupled with the file's main class. Are the support classes standalone, or are they useful on their own? For example, if a method in a class needs a special comparison for sorting some objects, it doesn't bother me a bit to bundle the comparison functor class into the same file as the method that uses it. I wouldn't expect to use it elsewhere and it doesn't make sense for it to be on its own.
If you are working on a team, keeping classes in separate files make it easier to control the source and reduces chances of conflicts (multiple developers changing the same file at the same time). I think it makes it easier to find the code you are looking for as well.
It can be bad from the perspective of future development and maintainability. It is much easier to remember where the Car class is if you have a Car.cs class. Where would you look for the Widget class if Widget.cs does not exist? Is it a car widget? Is it an engine widget? Oh maybe it's a bagel widget.
The only time I consider file locations is when I have to create new classes. Otherwise I never navigate by file structure. I Use "go to class" or "go to definition".
I know this is somewhat of a training issue; freeing yourself from the physical file structure of projects requires practice. It's very rewarding though ;)
If it feels good to put them in the same file, be my guest. Cant do that with public classes in java though ;)
You should refrain from doing so, unless you have a good reason.
One file with several small related classes can be more readable than several files.
For example, when using 'case classes', to simulate union types, there is a strong relationship between each class.
Using the same file for multiple classes has the advantage of grouping them together visually for the reader.
In your case, a car and a door do not seem related at all, and finding the door class in the car.cs file would be unexpected, so don't.
As a rule of thumb, one class/one file is the way to go. I often keep several interface definitions in one file, though. Several classes in one file? Only if they are very closely related somehow, and very small (< 5 methods and members)
As is true so much of the time in programming, it depends greatly on the situation.
For instance, what is the cohesiveness of the classes in question? Are they tightly coupled? Are they completely orthogonal? Are they related in functionality?
It would not be out of line for a web framework to supply a general purpose widgets.whatever file containing BaseWidget, TextWidget, CharWidget, etc.
A user of the framework would not be out of line in defining a more_widgets file to contain the additional widgets they derive from the framework widgets for their specific domain space.
When the classes are orthogonal, and have nothing to do with each other, the grouping into a single file would indeed be artificial. Assume an application to manage a robotic factory that builds cars. A file called parts containing CarParts and RobotParts would be senseless... there is not likely to be much of a relation between the ordering of spare parts for maintenance and the parts that the factory manufactures. Such a joining would add no information or knowledge about the system you are designing.
Perhaps the best rule of thumb is don't constrain your choices by a rule of thumb. Rules of thumb are created for a first cut analysis, or to constrain the choices of those who are not capable of making good choices. I think most programmers would like to believe they are capable of making good decisions.
The Smalltalk answer is: you should not have files (for programming). They make versioning and navigation painful.
One class per file is simpler to maintain and much more clear for anyone else looking at your code. It is also mandatory, or very restricted in some languages.
In Java for instance, you cannot create multiple top level classes per file, they have to be in separate files where the classname and filename are the same.
(C#) Another exception (to one file per class) I'm thinking of is having List in the same file as MyClass. Where I envisage using this is in reporting. Having an extra file just for the List seems a bit excessive.