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SDL input problems...

Started by BloodLust666 Dec 5, 2005 at 10:23 PM 15 replies 4.3k views

Original Post

Dec 5, 2005 at 10:23 PM

[source lang=C++]
if (SDL_Init( SDL_INIT_EVERYTHING) < 0)
   return cWUtility::ErrorLog.Write("cWInput::Init()");

SDL_EVENT   m_Event;
Uint8       *m_KeyState;
Uint8       m_MouseState;
long        m_AbsX, m_AbsY, m_RelX, m_RelY;


SDL_PollEvent( &m_Event );
SDL_EnableUNICODE( 1 );

m_KeyState = SDL_GetKeyState(NULL);

while (loop)
{
   SDL_PollEvent( &m_Event );
   SDL_PumpEvents();
   m_MouseState = SDL_GetMouseState((int*)m_AbsX, (int*)m_AbsY);
   SDL_GetRelativeMouseState((int*)m_RelX, (int*)m_RelY);

   if ( MYGetKeyState(SDL_ESCAPE))
      exit();
}

bool MYGetKeyState(long Key)
{
   if (m_KeyState[Key] == 1 )
     return true;
   return false;
}

for some reason none of my keyboard and mouse events are working.. it's not seeing that anything is being pressed (of course this is a very simplified version of what i really have coded) is there anything wrong with that?

Nairb

Dec 5, 2005 at 11:51 PM

The problem with your keyboard inputs can be explained because the
m_KeyState = SDL_GetKeyState(NULL) should be within your main loop.

Also, I think you're calling SDL_GetMouseState incorrectly. It should look something like:
m_MouseState = SDL_GetMouseState( &m_AbsX, &m_AbsY );

Cheers,
--Brian

BloodLust666

Dec 6, 2005 at 6:06 AM

ohhh, ok. what about pollevent() and pumpevents()? should i have those in my main loop?

Kylotan

Dec 6, 2005 at 8:37 AM

If you're not using that SDL_Event object, you don't need SDL_PollEvent at all. You will need SDL_PumpEvents, however.

BloodLust666

Dec 6, 2005 at 9:57 AM

Alright. How's the order go in the loop? should i pump events THEN getkeystate? for vice-versa?

Also, what's the purpose of using the SDL_EVENT, and polling the event?

rip-off

Dec 6, 2005 at 1:15 PM

Quote:
Original post by EvilKnuckles666
Alright. How's the order go in the loop? should i pump events THEN getkeystate? for vice-versa?

Also, what's the purpose of using the SDL_EVENT, and polling the event?

the event queue is central to SDL's event handling. if you do not empty the queue( by polling over every element and dealing with those you want ) your application will become unresponsive. you need to do that regularly.

the "snapshot" input functions can then be used, but they are not a complete replacement for polling

BloodLust666

Dec 6, 2005 at 1:45 PM

alright, i get the part about pollevent().. kinda, but what if there are 2 buttons being pressed at the same time?

can someone post some examples using pollevent() AND pumpevents() and event getkeystate()?

BloodLust666

Dec 6, 2005 at 2:45 PM

hmm... would i be able to just have something that looks like this?

[source lang=C++]bool Run() {    static SDL_Event s_Event;        // main loop    while (1)    {      SDL_PollEvent(&s_Event);      static unsigned char *s_Keys = SDL_GetKeyState(NULL);      static unsigned int SDLK_ALT = (SDLK_LALT | SDLK_RALT);      if (s_Keys[SDLK_ALT] && s_Keys[SDLK_F4])          break;      SDL_PumpEvents();    }    return true;}

also:
so the pollevent() needs to be at the top with the getkeystate() and the pumpevents() needs to be at the bottom once i'm done checking the states and whatnot?

edit:
since the SDL_EVENT only checks one key, and i'm going to use the getkeystate() anyway? could i just avoid using pollevent() completely? or would i have to do just what i'm doing in that code i posted and just ahve a call to it?

Drew_Benton

Dec 6, 2005 at 3:26 PM

I may be mistaken, but won't the line:

static unsigned char *s_Keys = SDL_GetKeyState(NULL);

Only call SDL_GetKeyState(NULL); once when that variable is first initialized first time around? Each subsequent call will not update the keystate since it's declared as static?

Of course, I go about all this input stuff a lot different from the ideas presented here, so rather than just post that, you can take a look at what I do if you want (lots of comments): Input Demo

rip-off

Dec 6, 2005 at 4:20 PM

Quote:
Original post by Anonymous Poster
It's just that I had keys in my functions, but not static, and since in the example I made a Run() function that ran the keys I decided to make it static, off-my-head. Atleast it's only an example... Since I got... anonymous I can't edit things so I'll just say it here:
*** Source Snippet Removed ***

Good luck!

C++

your use of statics is unnessecary and adds nothing but possible confusion and bugs.

only consider statics when you need to retain data across function calls, which for c++ means making an object usually.

the lowdown on SDL events:

you _must_ call SDL_PollEvent(...) to clear the event queue. your application will not run correctly on some systems without periodically running pollevent.

calls to GetKeyState and GetMouseState are just handy ways of accessing an input device. you can get exactly the same information from polling events.

problems can occur when detecting mulitiple keypresses. basically, sometimes if you hold down 2 or 3 keys, no program can detect them, (on windows) you can try this out in notepad. try pressing p, then y then t then r without releasing any of them.

on my system, you cant simultaneously detect all of them. your application will get the same data then using Poll()ing or Get*State()ing...

rip-off

Dec 6, 2005 at 6:00 PM

Quote:
Original post by Anonymous Poster
Quote:
Original post by rip-off
Quote:
Original post by Anonymous Poster
It's just that I had keys in my functions, but not static, and since in the example I made a Run() function that ran the keys I decided to make it static, off-my-head. Atleast it's only an example... Since I got... anonymous I can't edit things so I'll just say it here:
*** Source Snippet Removed ***

Good luck!

C++

your use of statics is unnessecary and adds nothing but possible confusion and bugs.

only consider statics when you need to retain data across function calls, which for c++ means making an object usually.

the lowdown on SDL events:

you _must_ call SDL_PollEvent(...) to clear the event queue. your application will not run correctly on some systems without periodically running pollevent.

calls to GetKeyState and GetMouseState are just handy ways of accessing an input device. you can get exactly the same information from polling events.

problems can occur when detecting mulitiple keypresses. basically, sometimes if you hold down 2 or 3 keys, no program can detect them, (on windows) you can try this out in notepad. try pressing p, then y then t then r without releasing any of them.

on my system, you cant simultaneously detect all of them. your application will get the same data then using Poll()ing or Get*State()ing...

I like your words. They are... 'wise'.

Anyways, 'Poll()ing' cannot give me all my keys. However, 'Get*State()ing' can. 'Get*State()ing' gives a snapshot... All the keys pressed. 'Poll()ing' gives you the event, so that's why when you press 'p' you get a 'p' and even if you still hold it and press something else you would get something else.

C++

depends on what you are doing.

some people prefer

if( leftkey ) movePlayerLeft();

i prefer

if( leftkeydown ) setPlayerVelocity( ... );
if( leftkeyup ) setPlayerVelocity( 0 );

its a bit more than that but you get the point...

Kylotan

Dec 10, 2005 at 8:09 AM

Seems to be a bit of confusion here... as I said earlier, if you use PumpEvents, you don't need PollEvent. (Unless there's a bug in SDL that I am not aware of.)

Also, you can track multiple keypresses using SDL_EVENT/PollEvent, but you have to watch for it yourself. When a keydown event comes in, you mark the key as down, and when a keyup comes in, you mark it as up. That way you can see when multiple keys are pressed. If you don't need the event handling for other purposes though, you may as well stick with GetKeyState.

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