Duplicate SDL event issue

aatwell · 01-02-2008, 04:00 PM

Hi folks,
I have an issue with a program I'm writing. I'm using SDL to capture keyboard events. When I press an arrow key (Left, Right, UP or Down), the program works just as it should. The problem arises when I press a second button. The first key pressed seems to remain in the queue and executes again and is immediately followed by the second command.

For example:
If I press the UP arrow, it moves an object up...then if I press the left arrow, it moves the object up and then to the left.

Does anyone know what might cause this?

- Andrew

dmail · 01-02-2008, 06:26 PM

Hmm is one of them a keydown followed by a keyup, or maybe its a key repeat as the button is still pressed. Would you post your event loop?

aatwell · 01-02-2008, 08:14 PM

I thought of that...so I made only the SDL_KEYUP have any action taken.

Code:

/*
#include //  blah....blah....blah
*/

int main()
{	// declarations, video, SDL_INIT //
	// blah...blah...blah...         //


	// MAIN LOOP EVENT //
	while(SDL_PollEvent(&event))
	{	switch(event.type)
		{	case SDL_KEYDOWN:
				break;
			case SDL_KEYUP:
				DoSomething(&event.key);
				break;
			case SDL_QUIT:
				break;
		}
	}

	// blah....blah....blah...       //
	return(0);
}


void DoSomething(SDL_KeyboardEvent *key)
{
	switch(key->keysym.sym)
	{       case SDLK_LEFT:
			printf("LEFT   KEY PRESSED.\n", stdout);
			fflush(stdout);
			break;
		case SDLK_RIGHT:
			printf("RIGHT  KEY PRESSED.\n", stdout);
			fflush(stdout);
			break;
		case SDLK_UP:
			printf("UP     KEY PRESSED.\n", stdout);
			fflush(stdout);
			break;
		case SDLK_DOWN:				   
			printf("DOWN   KEY PRESSED.\n", stdout);      
			fflush(stdout);
			break;
		case SDLK_ESCAPE:
			printf("ESCAPE KEY PRESSED.\n", stdout);
			fflush(stdout);
			break;
		default:
			break;
	}
}

dmail · 01-03-2008, 04:46 AM

I did suspect that you were falling through the case statement yet this seems not to be the case(is this the actual code? ) and I am unsure of why this is happening; but I have to say I think you are handling key presses wrongly. Only detecting a key release is a strange method to use.
is this for a game?
which version of SDL are you using
which operating system?
How old is the keyboard you are using?

aatwell · 01-03-2008, 11:25 AM

Yeah. This is for a game. It does the same thing under Fedora Core 6 and 7 using SDL-1.2.11-1.fc6 and SDL-1.2.12-1.fc7 respectively. My keyboard is a standard keyboard.

You mentioned that only using the key release is strange...but what is the standard method. I did this to try and resolve the double action issue, but it didn't resolve it.

Thanks,
Andrew

Fidori · 01-04-2008, 02:15 PM

Is the while loop inside another loop? This is working okay for me on Ubuntu 7.10:

Code:

int main(int argc, char *argv[])
{
        SDL_Event event;

        if (SDL_Init(SDL_INIT_VIDEO) != 0
            || SDL_SetVideoMode(500, 500, 0, SDL_ANYFORMAT) == NULL) {
                fprintf(stderr, "error: %s\n", SDL_GetError());
                return EXIT_FAILURE;
        }

        for (;;) {
                while (SDL_PollEvent(&event)) {
                        switch (event.type) {
                        case SDL_KEYUP:
                                printf("key up: %d\n", event.key.keysym.sym);
                                break;
                        case SDL_QUIT:
                                SDL_Quit();
                                return EXIT_SUCCESS;
                        default:
                                break;
                        }
                }
        }
}

aatwell · 01-04-2008, 02:35 PM

Hmmm..... Actually it is inside another loop. I have a while inside a while. That was done to solve another issue with closing the program without error. I'll see what happens... Thanks. -Andrew