use SDL to read joystick/gamepad input

samel_tvom · 10-06-2006, 05:47 PM

Hi!

I have written a really ugly program in C that reads input from my gamepad and then generates xevents, or sends keycodes, whatever you wanna call it, using the Xtest library (#include <X11/extensions/XTest.h>). So that for example, when you press the X-button on the gamepad, I make X generate a "press return key event".

I read byte by byte from /dev/input/js0 and I figured that maybe all gamepads and joysticks haven't got the same output, so I wanted to use something generic to read joystick/gamepad input. Something like SDL maybe.

But I can't get SDL to read input when the SDL app window is passive. I rather not use a gui at all since I only want to launch a daemon that listens for gamepad inputs and then makes xevents.

Any idea how to do this? Any other lib to use?

And yes, I have heard of qjoypad. http://qjoypad.sourceforge.net/

Thanks!

tuxdev · 10-07-2006, 11:17 AM

Where's the code? Can't say why it is doing whatever it is doing without looking at the code. Make sure you wrap them in [code] tags to preserve indentation.

osor · 10-07-2006, 03:33 PM

Quote:

Originally Posted by samel_tvom

Hi!

I have written a really ugly program in C that reads input from my gamepad and then generates xevents, or sends keycodes, whatever you wanna call it, using the Xtest library (#include <X11/extensions/XTest.h>). So that for example, when you press the X-button on the gamepad, I make X generate a "press return key event".

I read byte by byte from /dev/input/js0 and I figured that maybe all gamepads and joysticks haven't got the same output, so I wanted to use something generic to read joystick/gamepad input. Something like SDL maybe.

But I can't get SDL to read input when the SDL app window is passive. I rather not use a gui at all since I only want to launch a daemon that listens for gamepad inputs and then makes xevents.

If you are going to use linux, the /dev/input/jsX interfaces all generate the same sort of output, regardless of manufacturer (IIRC, joydev is the driver responsible for this). Why are you reading one byte at a time? You should read more bytes (maybe 8?). Whatever the number, it's probably better to use sizeof(whatever_the_js_event_struct_is_called) instead. It's been awhile, but I think upon the opening of the device, joydev spits out some stuff (i.e., fake events with special meaning) that's supposed to tell you about the number of buttons/axes/etc. on this specific joypad. There are also some IOCTL's to figure this out.

You can use the linux joydev API directly instead of trying to find a library with its own joystick API (unless, of course, you want some sort of cross-platform portability). Documentation should be in the linux source tree.

samel_tvom · 10-07-2006, 05:02 PM

Yeah, I found out later on that using the js_event is probably the way to go. However, I can't seem to compile the program. Maybe you guys could help me.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <linux/joystick.h>

int main() {
	int len;
	js_event msg;
	char* device = "/dev/input/js0";
	FILE *f = fopen(device, "rb+");
	
	while(1) {
		read(f, &msg, sizeof(js_event));
		if (len == (int) sizeof(js_event)) {
			printf("wii\n");
		}
	}
	
	return 0;

}

I try to compile with "gcc test.c" but I get
‘js_event’ undeclared (first use in this function)
and I can't figure out what lib the #include <linux/joystick.h> whould be in.
What args should I have to gcc?

Thanks!

samel_tvom · 10-07-2006, 05:09 PM

Hehe, I might add that the program I just posted is just a test program to get the reading from the joystick work =)

Now that I found out that using linux/joystick.h my old program (shitty and all) is useless, but I'll post it anyways.

There's some code from qjoypad, it's GPL'ed

Code:

// gcc gamepad.c -lXtst

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>

#include <X11/extensions/XTest.h>
#include <X11/Xlib.h>

// so that we get the definintions of keys in keysymdef.h
#define XK_LATIN1
#define XK_MISCELLANY

#include <X11/keysymdef.h>


typedef struct xevent xevent;

struct xevent {
        int type;
        unsigned int value1;     //button, keycode, or x
        unsigned int value2; //y
};


void sendevent(xevent e, Display *display) {
	if (e.value1 == 0 && e.value2 == 0) return;
	if (e.type == 4) {
		XTestFakeRelativeMotionEvent(display, e.value1, e.value2, 0);
	}
	else {
		if (e.type == 0 || e.type == 1) {
			XTestFakeKeyEvent(display, e.value1, (e.type == 1), 0);
		}
		else if (e.type == 2 | e.type == 3) {
			XTestFakeButtonEvent(display, e.value1, (e.type == 3), 0);
		}
	}
	XFlush(display);
}




int main() {
	unsigned char down_down[] = {255, 127, 2, 1};
	unsigned char down_up[] = {0, 0, 2, 1};
	unsigned char up_down[] = {1, 128, 2, 1};
	unsigned char up_up[] = {0, 0, 2, 1};

	unsigned char left_down[] = {1, 128, 2, 0};
	unsigned char left_up[] = {0, 0, 2, 0};
	unsigned char right_down[] = {255, 127, 2, 0};
	unsigned char right_up[] = {0, 0, 2, 0};
	
	unsigned char anybutton_down[] = {1, 0, 1, 1};

	Display *display;
	display = XOpenDisplay(":0.0");	
	xevent e;

	char* device = "/dev/input/js0";
	unsigned char packet[8];
	unsigned char key[4];	

	FILE *f = fopen(device, "wb+");

	// read away stuff at the begining
	void *tmp = malloc(8*12*sizeof(char));
	fread(tmp, sizeof(char)*8*12, 1, f);
	free(tmp);
	
	while(1) {
		fread(&packet, sizeof(char)*8, 1, f);
		key[0] = packet[4];
		key[1] = packet[5];
		key[2] = packet[6];
		key[3] = packet[7];
		
		if(strncasecmp(key, up_down, 4) == 0) {
			e.type = 1;
			e.value1 = XKeysymToKeycode(display, XK_Up);
			sendevent(e, display);
			e.type = 0;
			sendevent(e, display);
			
		}
			
		if(strncasecmp(key, down_down, 4) == 0) {
			e.type = 1;
			e.value1 = XKeysymToKeycode(display, XK_Down);
			sendevent(e, display);
			e.type = 0;
			sendevent(e, display);
		}
		if(strncasecmp(key, left_down, 4) == 0) {
			e.type = 1;
			e.value1 = XKeysymToKeycode(display, XK_Left);
			sendevent(e, display);
			e.type = 0;
			sendevent(e, display);

		}
		if(strncasecmp(key, right_down, 4) == 0) {
			e.type = 1;
			e.value1 = XKeysymToKeycode(display, XK_Right);
			sendevent(e, display);
			e.type = 0;
			sendevent(e, display);
		}
		if(strncasecmp(key, anybutton_down, 4) == 0) {
			e.type = 1;
			e.value1 = XKeysymToKeycode(display, XK_Return);
			sendevent(e, display);
			e.type = 0;
			sendevent(e, display);
		}
			
		usleep(1000);
	}
	
	return 0;

}

samel_tvom · 10-07-2006, 05:16 PM

Hmm, I should think before I post, anyways. Since qjoypad is written in c++ maybe I should use

Code:

struct js_event msg;

However, adding the "struct" did no difference.

osor · 10-07-2006, 10:02 PM

Quote:

Originally Posted by samel_tvom

Hmm, I should think before I post, anyways. Since qjoypad is written in c++ maybe I should use

Code:

struct js_event msg;

However, adding the "struct" did no difference.

The struct is not typedef'd, so you need to add struct everytime you use it (i.e., wherever it says js_event, change it to struct js_event).

Also, currently, you don't do anything to len, rendering your program useless.

You could change

Code:

read(f, &msg, sizeof(struct js_event));
	if (len == (int) sizeof(struct js_event)) {

to

Code:

len = read(f, &msg, sizeof(struct js_event));
	if (len == (int) sizeof(struct js_event)) {

or even

Code:

if ( (len = read(f, &msg, sizeof(struct js_event))) == (int) sizeof struct js_event) {

Someone needs to brush up on their C.

samel_tvom · 10-09-2006, 03:11 PM

Yepp, that's totally true =)

Thanks for the info, really appreciate it!