• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
suliman

Modify functions from generic class? (c++)

6 posts in this topic

Hi

I have many classes in my gameengine. They perform verious standard things (used in all games) but i also want to be able to do game-specific stuff with them, preferably without making inherited classes from the generic class.

 

Can i declare an "empty function" for the class that i fill differently depending on the game?

And maybe also add some game-specific variables?

 

Thanks

Erik

0

Share this post


Link to post
Share on other sites

What language?

 

Why are you trying to avoid inheritance? You could do something like this using function pointers but it would be about as pointless as possible.

0

Share this post


Link to post
Share on other sites

c++ is the language (see topic)

Since i want to remain uniformity. And be able to reuse some stuff. Often i want to do very similar stuff just modify something.

0

Share this post


Link to post
Share on other sites
Since the question is extremely generic the answers will end up being extremely generic:
- use composition
- use polymorphism despite your reservations
- use compile-time polymorphism
- embed a scripting language
1

Share this post


Link to post
Share on other sites

Assuming you are writing good code and predominantly using interface inheritance instead of implementation inheritance, you can always derive from an interface that provides your "general" functionality, and have each specific game add an interface for its own specific functionality.

0

Share this post


Link to post
Share on other sites

Can i declare an "empty function" for the class that i fill differently depending on the game?

 
At compile time? Sure - just declare the function in the engine's header files, but only define it in the game-specific source files.
//MyClass.h - Engine header file
class MyClass
{
     public:
     void function();
     void gameSpecificFunction();
};
.
//MyClass.cpp - Engine source file
void MyClass::function()
{
     //Code....
}
.
//MyClass_Game.cpp - Game-specific source file.
void MyClass::gameSpecificFunction()
{
     //Code....
}
.
If you mean at runtime you want the function to change? Sure - just use function pointers.
typedef std::function<void(float,int)> MyFunction;
 
class MyClass
{
     public:
     void SetFunctionToUse(MyFunction function) { functionToCall = function; }
 
     void CallFunction(float myFloat, int myInt)
     {
          //Check if a function has been set.
          if(functionToCall)
          {
                 //If so, call the function.
                 functionToCall(myFloat, myInt);
          }
     }
     
     private:
     MyFunction functionToCall;
};
.

And maybe also add some game-specific variables?

Well, that's slightly more difficult, but yes. You can use the pImpl idiom very effectively for this.
 
//MyClass.h - Engine header file
class MyClass
{
     public:
     void function();
     void gameSpecificFunction();
 
     private:
     int normalVariable;
     //The game-specific variables don't go here yet.
     
     private:
     //We tell the compiler a class called 'MyClass::Implementation' exists, but we don't define it yet.
     //This is a class within a class (in terms of namespace).
     class Implementation; 
     
     std::unique_ptr<Implementation> pImpl; //A pointer to the 'Implementation' class that we haven't yet defined.
};
.
//MyClass.cpp - Engine source file
 
//I'm including a _source_ file here, not a header file.
#include "../Game/MyClass_Implementation.cpp"
 
MyClass::gameSpecificFunction()
{
    //Call the Implementation's version of the function.
    pImpl->realFunction();
}
.
//MyClass_Implementation.cpp - Game-specific source file
 
//NOW we define MyClass::Implementation.
//I like to make pImpl's be 'structs' since they are public by default.
struct MyClass::Implementation
{
     //Game-specific variables.
     int meow = 357;
     
     //Game-specific function implementation
     void realFunction()
     {
           //...code...
     }
 
};
.
However, using these in some situations may indicate bad architecture - I would give it some serious thought and ask myself what I am actually needing, why I'm needing it, and what would be the best way to implement it. Edited by Servant of the Lord
1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0