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Game Input Timing


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#1 Zenroth   Members   -  Reputation: 127

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Posted 23 October 1999 - 07:59 AM

Ok i have recently run into a bit of a problem ive tried a few things to fix the problem,and they didnt work well. So here i am.

Ok i am using directinput for checking keys in my logic loop. Basicly

Keyboard->GetDeviceState( sizeof(diks), &diks );

int KEY(int key){
return diks[key] & 0x80;}

if (KEY(DIK_ESCAPE)) PostMessage(hwnd, WM_DESTROY,0,0);

Ok this works great so far. Now i come to my problem

if (KEY(DIK_UP) && KEY(DIK_LEFT))player1.y-=1, player1.x-=1, player1.dir = DIR_NORTH_WEST;

Ill tell you a bit more bout what im trying to do so that the above might make a little bit more sence. Im using 8-way graphics and i have bitmaps for each direction. The problem is i can never get the diagonal to work. I mean they work if i hold them down but i can't ever get the direction to stay as a diagonal. I guess it sees that one of the direction keys was down for a millisecond longer than the other so it goes up or left ect. So what i need i think is some type of a delay. Sleep(1) works perfectly but kills my framerate very badly.

Any Thoughts on how to get this working?


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#2 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 23 October 1999 - 07:10 AM

I haven't used GetDeviceState- but I'm guessing it gets the current up/down status of all the keys right?
Also, I'm confused about why adding a delay makes a difference. Maybe it has something to do with key repeat? The second key pressed will repeatedly be set as pressed while the first is only pressed once?

Anyway here's an alternative way, a bit uglier, but it works for me-

bool GetKeyEvent(unsigned char &Scancode, bool &Pressed)
{
DIDEVICEOBJECTDATA TheEvent;
unsigned long ArrayLen= 1;
HRESULT Result;

Result= Keyboard->GetDeviceData(sizeof(DIDEVICEOBJECTDATA), &TheEvent, &ArrayLen, 0);
if (!SUCCEEDED(Result))
{
return false; // no keys pressed
}

if (ArrayLen == 1)
{
Scancode= (unsigned char) TheEvent.dwOfs;
if (TheEvent.dwData & 0x80)
Pressed= true;
else
Pressed= false;
return true;
}
else
return false;
}


Call this in your main loop:

while (GetKeyEvent(Scancode, Pressed))
register this key as pressed/released

You'll need an array of the keys you want to use in your program, and mark them as down/up in the above loop.

Then after the loop you can check your keyarray for the pressed keys.

This also fixes a problem you might run into later, if you have a shoot key for instance- it's possible to press and release the key inbetween calls to GetDeviceState, in which case the keypress would not be caught.

hope this is somewhat useful


#3 Zenroth   Members   -  Reputation: 127

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Posted 23 October 1999 - 07:30 AM

Well how im doing keyboard input is im using immediate data and not buffered input. I dont check the entire keyboard. I just check to see if that one key is down.

I guess i might need to look into buffered directinput,but dont i have to worry about overflows and things then?


#4 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 23 October 1999 - 07:59 AM

Yes you'll have to deal with overflow, but it's not hard. Use the SetProperty function when you're setting up the keyboard:

DIPROPDWORD Props;
Props.diph.dwSize= sizeof(Props);
Props.diph.dwHeaderSize= sizeof(DIPROPHEADER);
Props.diph.dwObj= 0;
Props.diph.dwHow= DIPH_DEVICE;
Props.dwData= 1024;
Keyboard->SetProperty(DIPROP_BUFFERSIZE, &Props.diph);

The dwData member is the buffersize, as long as you're checking the buffer every so often it should never overflow with a big enough buffer.
If it does overflow, directinput handles it- new data is lost, but it won't crash.





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