Hi everybody,

I am thinking in how to implement my game engine and started with the input system. I read http://www.gamedev.net/blog/355/entry-2250186-designing-a-robust-input-handling-system-for-games/ and came up with this. What i have is an InputManager that handles SDL way of input and send them to a list of InputContexts. Each InputContext has a pointer to IInputListenner, that is the one who handles the input, but the InputContext has the role of translate the InputEvent object into a game message. And is here that i dont know how to really do it. I thought put the information needed by InputContext inside a XML file, but i dont know how to parse a XML into a generic type of data, which may have one, two or three values inside it and pass it to game logic.

My problem isn't how to load a XML file, it is how do i create a generic MessageObject that my game can handle.

InputManager.h:

class InputManager
{
public:
        static InputManager* getInstance();

        void dispatchEvents();

        void registerContext(InputContext* c);
        void deregisterContext(InputContext* c);
private:
        InputManager();
        static InputManager* instance;
        std::list<InputContext*> contexts;
}

The only interesting function is the dispatchEvent(). which is called every frame:

void InputManager::dispatchEvents()
{
	SDL_Event event;
	while(SDL_PollEvent(&event) != 0)
	{
		InputEvent inputEvent;
		std::map<unsigned int, InputEventType>::iterator it = inputEventMap.find(event.type);
		if(it == inputEventMap.end())
		{
                        std::cout<<"Unknown Event"<<std::endl;
            		continue;
		}
		inputEvent.type = it->second;
		inputEvent.timestamp = event.common.timestamp;
		if(inputEvent.type == KEYBOARD)
		{
			inputEvent.key = mapKeyInput(event);
		}
		else if(inputEvent.type == MOUSE)
		{
			inputEvent.mouse = mapMouseInput(event);
		}
		for(std::list<InputContext*>::iterator it = contexts.begin(); it != contexts.end(); it++)
		{
			if((*it)->dispatch(inputEvent))
			{
				break;
			}
		}
	}
}

Here is a possible syntax for the XML :

<?xml version="1.0" encoding="ISO-8859-1"?>
<context>
   <key value="W" pressed="true" message="MOVE_FORWARD"/>
   <key value="SHIFT + W" pressed="true" message="RUN_FORWARD"/>
...
   <mouse value="MOTION" message="CAMERA_MOTION">
      <param value="X" inverted="false"/>
      <param value="Y" inverted="false"/>
   </mouse>
</context>

i dont like the idea of passing the messages as string because string comparison isnt efficient. I am open to suggestions.

Thanks in advance.

Thanks for your reply.

Ok, let me see if i got it. I dont need handlers, because the inputs goes direct to my buffer and the buffer is directed accessed from logic update right?

But i still need a way to parse the input data into game data, and this must be relative to the context that i'm using. The way i see, a player would have a context, a menu would have a context and so on. Then whenever i would read the input, i would pass something like message = currentContext.parse(input); and check whatever i need to execute the message. So i still need a way to parse my XML into a generic message or there is a more elegant way of doing it?

Also, could you explain me why singleton is wrong? its not the first time i see it, but no one pointed me an article or explained why.

Also, could you explain me why singleton is wrong? its not the first time i see it, but no one pointed me an article or explained why.

Generally because they're just a sign of a poor engine architecture and layout, they also make silly assumptions like that you will only ever have one instance of something. Want to make a second input handler to accept networked input? Sorry, only one. Want to make a second render controller for another opengl context? Sorry only one here.

They also are basically globals in OOP sheep's wool and have nearly all the same problems as them. It is usually considered rather bad design choice to allow any section of a program to reach a claw out and stick itself in different sections of the engine without any sort of control or reduction of visibility. I believe L. Spiro mentions it in a few blog posts too as to why you would ever possibly want more than one copy of a subsystem like rendering for multiple contexts.

But really if you search the forum I'd be shocked if you don't find a thousand debate topics on the subject. My opinion stands at, they are a valid design idea but with the exception of a few closet cases in languages like C#, you should prefer to not use them, they'll just promote lazy design that will bite you hard later, especially if you start threading.

Thanks for the articles, now i see the way i was using ( and taught ) was wrong. About the input, i changed to an event manager that i saw in Game Code Complete 4, using fast delegates http://www.codeproject.com/Articles/11015/The-Impossibly-Fast-C-Delegates. Now i am going to learn how to do it multithread so i can properly handle SDL.

So much to learn..

Thanks for the help .