2 keys down

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2 keys down

 
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  #1
Nov 2nd, 2009
hi...i'm making a game that uses the direction arrows and fires with space...the problem is that when i keep holding 2 keys it makes only the behavior of one....can any1 tell me what i shall do
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  #2
Nov 2nd, 2009
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Originally Posted by kadamora View Post
hi...i'm making a game that uses the direction arrows and fires with space...the problem is that when i keep holding 2 keys it makes only the behavior of one....can any1 tell me what i shall do
Could you post the code you're using to track key up/down status? That would help us find what's going wrong.
--smg
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Nov 2nd, 2009
AFAIK Normal Windows development (e.g. what you get with normal Visual Studio installations) does not handle multiple key presses, not including modifier keys (ctrl, alt, and shift.) The problem is Windows supports two types of key press events: KeyDown/Up and Repeat. Key up and down is great, but if you hold a key down, it fires Repeat until that key is let go. Not handy if you are trying to hold 2 keys down at once.

In order to handle multiple simultaneous non-modifier keys, you need to use the DirectInput portion of the DirectX SDK (google directx sdk directinput), and specifically the GetCurrentKeyboardState function.

There are definitely other ways to do this (I am sure there are a lot of existing game engines out there) but the Microsoft Way (TM) is DirectX. Other alternatives will probably appear if you search "windows game engine" , "windows game sdk" or "windows alternative keyboard handler." Good luck!
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  #4
Nov 2nd, 2009
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Originally Posted by gusano79 View Post
Could you post the code you're using to track key up/down status? That would help us find what's going wrong.
sure...here it is...
i use speed to accelerate
C# Syntax (Toggle Plain Text) 
  1.  void nagy_KeyDown(object sender, KeyEventArgs e)
  2.         {
  3.  
  4.             if (e.KeyCode == Keys.Left)
  5.             {
  6.                 leftspeed += 5;
  7.                 rightspeed = 0;
  8.  
  9.  
  10.             }
  11.  
  12.             if (e.KeyCode == Keys.Right)
  13.             {
  14.                 rightspeed += 5;
  15.                 leftspeed = 0;
  16.             }
  17.             if (e.KeyCode == Keys.Space)
  18.             {
  19.                 leaser = true;
  20.             }
  21.  
  22.  
  23.         }
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  #5
Nov 2nd, 2009
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Originally Posted by mikiurban View Post
AFAIK Normal Windows development (e.g. what you get with normal Visual Studio installations) does not handle multiple key presses, not including modifier keys (ctrl, alt, and shift.)
To clarify, the .NET Framework doesn't provide automatic handling of multiple key presses. You can still handle them yourself.

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Originally Posted by mikiurban View Post
The problem is Windows supports two types of key press events: KeyDown/Up and Repeat. Key up and down is great, but if you hold a key down, it fires Repeat until that key is let go. Not handy if you are trying to hold 2 keys down at once.
This is what's keeping your code from working right--when you hold one key down and press another at the same time, you stop getting repeats from the first key, and start getting them from the second.

As long as your game logic is coupled to keyboard event handling, you'll always need a new key event to do something in game logic. Because you never get repeats for more than one key at a time, you won't be able to do two actions at once.

The solution? Decouple keyboard event handling from game logic.

First, you need a place to keep track of which keys are currently down. If you only have a few keys you're interested in, you might have a couple of lines like this:

C# Syntax (Toggle Plain Text) 
  1. private bool spaceKeyDown = false;

Then, handle the "key down" event:

C# Syntax (Toggle Plain Text) 
  1. private void MainFormKeyDown(object sender, KeyEventArgs e)
  2. {
  3.     if(e.KeyCode == Keys.Space)
  4.     {
  5.         spaceKeyDown = true;
  6.     }
  7. }

Handle the corresponding "key up" event:

C# Syntax (Toggle Plain Text) 
  1. private void MainFormKeyUp(object sender, KeyEventArgs e)
  2. {
  3.     if(e.KeyCode == Keys.Space)
  4.     {
  5.         spaceKeyDown = false;
  6.     }
  7. }

Then the trick is to run your game logic in a separate thread, for example, with a Timer:

C# Syntax (Toggle Plain Text) 
  1. private void KeyMonitorTick(object sender, EventArgs e)
  2. {
  3.     if(spaceKeyDown)
  4.     {
  5.         // do something useful here
  6.     }
  7. }

This way, the timer tick method is able to check the "down" status of any key you've tracked using the key handlers, and you can handle more than one key being down at a time.

There are a few ways to skin this particular cat--some are easier to code, some are more general-purpose, others are more thread-safe... attached is a sample Windows Forms application that tracks multiple keypresses in a slightly different way than the above code.

Final note: There will be certain combinations of keys you won't ever be able to handle simultaneously, simply because keyboards won't send key events for them. It may differ from keyboard to keyboard, and usually they're reasonable. For example, I can hold any two (and sometimes three) arrow keys down on the keyboard I'm using right now and get proper events for those keys, but I never get "key down" events from all four simultaneously.
Attached Files
File Type: zip MultipleKeys.zip (20.5 KB, 8 views)
--smg
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  #6
Nov 3rd, 2009
this is so great......i'm very grateful to you, and the program
thnx alot
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  #7
Nov 3rd, 2009
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Originally Posted by gusano79 View Post
To clarify, the .NET Framework doesn't provide automatic handling of multiple key presses. You can still handle them yourself.

<snip>

This is what's keeping your code from working right--when you hold one key down and press another at the same time, you stop getting repeats from the first key, and start getting them from the second.

<snip>

The solution? Decouple keyboard event handling from game logic.
Thanks Gusano, for clarifying, and giving an excellent example.
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