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Troubles with keyboard input.


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#1 Soan   Members   -  Reputation: 100

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Posted 03 June 2011 - 08:08 PM

Hi, I'm currently studying programming(doing C++) and game dev at a local school, and we've recently started our 2d sprite game projects, and I've encountered a problem that even my tutor isn't sure why it's happening. What it boils down too, is that windows does not seem to be picking up when two keys are released at the same time, which ends up in the character continuing to move in whatever direction he was moving in without any keys being pressed.

I have the following code in my winproc:


case WM_KEYUP:
		{
			if (VK_LEFT == _wparam)
			{
				if (HeroSprite->GetDirection() == WALK_LEFT)
				{
					HeroSprite->StopWalking();
				}
			}

			if (VK_RIGHT == _wparam)
			{
				if (HeroSprite->GetDirection() == WALK_RIGHT)
				{
					HeroSprite->StopWalking();
				}
			}

			if (VK_SPACE == _wparam)
			{
				if (!((GetAsyncKeyState(VK_RIGHT) & 0x8000) == 0x8000) &&
					!((GetAsyncKeyState(VK_LEFT) & 0x8000) == 0x8000))
				{ 
					if (HeroSprite->GetWalkingState())
					{
						HeroSprite->StopWalking();
					}
				}
			}
		}
		break;

What I want to happen, is if either of the movement keys (left and right arrow keys), are released at the same time the attack key(space bar) is hit, for the character to stop moving.


Any advice or suggestions on how I could possibly get this to happen would be great. :)

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#2 DarkRonin   Members   -  Reputation: 610

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Posted 04 June 2011 - 05:19 AM

What if you break; at the end of the if(VK_... statement.

As it is unlikely that you could release two keys simultaneously on the one loop. The next coming loops should catch the second key release and you are good to go.

#3 scgames   Members   -  Reputation: 1977

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Posted 04 June 2011 - 03:32 PM

That should probably be a switch statement or a series of if-else's rather than a series of 'if' statements (since '_wparam' can only have one value).

Also, if you're going to use leading underscores for symbols, be sure you're familiar with what the standard has to say about them.

As for your problem, it seems unlikely to me that Windows would not correctly report multiple key releases in a single polling cycle. As such, I'm guessing the problem is due to a logic error in your code somewhere (although I can't say that for sure).

In any case, the first thing I'd probably do is add some breakpoints or debug output to determine which blocks of code are actually being executed.

#4 Soan   Members   -  Reputation: 100

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Posted 04 June 2011 - 05:39 PM

Also, if you're going to use leading underscores for symbols, be sure you're familiar with what the standard has to say about them.


That's actually part of my schools naming standards for variables, where anything that's a parameter of a function gets an underscore in front of it. If there's some other meaning behind it as well I can't say I remember them having covered it.

Not long after I posted this I actually had a brain wave and was able to fix it. Was just a bit of a logic change in where I put the GetAsyncKeyState call. Will definitely change it to a switch or if-else statements though, as that does make more sense.




#5 scgames   Members   -  Reputation: 1977

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Posted 04 June 2011 - 05:47 PM

That's actually part of my schools naming standards for variables, where anything that's a parameter of a function gets an underscore in front of it.

It's probably not something that'd be covered in your class, I wouldn't imagine. In any case, leading underscores for method parameter names should be ok. (If you're curious about the details, just search the forums for 'leading underscores'.)

#6 DarkRonin   Members   -  Reputation: 610

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Posted 05 June 2011 - 03:05 AM

What the? You are using WM_KEYUP and GetAsyncKeyState() at the same time? :blink:

You don't need GetAsyncKeyState() if you are processing key presses with WM_KEYUP.

#7 A1P4A_0M3GA   Members   -  Reputation: 89

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Posted 05 June 2011 - 03:50 AM

Ok, here's what you need to do:

Set up two switches, one for keydown and one for keyup events. Then put a case for each keydown and keyup event in the respectful switch.

I apologize in advance for not using the proper code.

switch(getKeyDown)	{
	case VK_LEFT: HeroSprite->GetDirection = WALK_LEFT; break;
	case VK_SPACE: HeroSprite->StopWalking; break;
/*...*/
}
switch(getKeyUp)	{
	case VK_LEFT: HeroSprite->StopWalking; break;
/*...*/
}

That seems like a more efficient and effective way to program your controls.
-A1P4A 0M3GA
Lead script writer on Scutum [http://www.gamedev.n...-entertainment/]
Team Member of Forcas Entertainment
Amateur programmer with C++ and SDL knowledge
Game Enthusiast




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