How to read low level mouse click position in linux . - c++

Question

I am using this code to read mouse events from the dev/input/event* in linux .
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/input.h>
#include <fcntl.h>
#define MOUSEFILE "/dev/input/event4"
int main()
{
int fd;
struct input_event ie;
if((fd = open(MOUSEFILE, O_RDONLY)) == -1) {
perror("opening device");
exit(EXIT_FAILURE);
}
while(read(fd, &ie, sizeof(struct input_event))) {
printf("time %ld.%06ld\ttype %d\tcode %d\tvalue %d\n",
ie.time.tv_sec, ie.time.tv_usec, ie.type, ie.code, ie.value);
}
return 0;
}
It gives me the results in the format :
time 1342517261.840285 type 2 code 0 value -1
'time' is the timestamp, it returns the time at which the event happened.
'code' is event code, for example REL_X or KEY_BACKSPACE, complete
list is in include/linux/input.h.
'value' is the value the event carries. Either a relative change for
EV_REL, absolute new value for EV_ABS (joysticks ...), or 0 for EV_KEY for
release, 1 for keypress and 2 for autorepeat.
when i click , i get the event but i don't get the position of the mouse on the screen , what is the way to get the position of the mouse on screen .
Edit 1:So as it turns out that i have to use the relative co-ordinates to get the mouse co-ordinates .I believe this is a common requirement so there might be libraries/pre-existing code that you can use to get the co-ordinates. Any info on this topic will be very useful .
Edit2 : SOLUTION
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/input.h>
#include <fcntl.h>
#include <X11/Xlib.h>
#define MOUSEFILE "/dev/input/event4"
int main()
{
int fd;
struct input_event ie;
Display *dpy;
Window root, child;
int rootX, rootY, winX, winY;
unsigned int mask;
dpy = XOpenDisplay(NULL);
XQueryPointer(dpy,DefaultRootWindow(dpy),&root,&child,
&rootX,&rootY,&winX,&winY,&mask);
if((fd = open(MOUSEFILE, O_RDONLY)) == -1) {
perror("opening device");
exit(EXIT_FAILURE);
}
while(read(fd, &ie, sizeof(struct input_event))) {
if (ie.type == 2) {
if (ie.code == 0) {
XQueryPointer(dpy,DefaultRootWindow(dpy),&root,&child,
&rootX,&rootY,&winX,&winY,&mask);
//rootX += ie.value;
}
else if (ie.code == 1) {
XQueryPointer(dpy,DefaultRootWindow(dpy),&root,&child,
&rootX,&rootY,&winX,&winY,&mask);
// rootY += ie.value;
}
printf("time%ld.%06ld\tx %d\ty %d\n",
ie.time.tv_sec, ie.time.tv_usec, rootX, rootY);
} else
printf("time %ld.%06ld\ttype %d\tcode %d\tvalue %d\n",
ie.time.tv_sec, ie.time.tv_usec, ie.type, ie.code, ie.value);
}
return 0;
}
XQueryPointer seems more convenient solution . Thanks , #perreal for the guidance .

Answer 1

You can get the initial position from X11, and use relative coordinates to track the pointer:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/input.h>
#include <fcntl.h>
#include <X11/Xlib.h>
#define MOUSEFILE "/dev/input/event6"
int main()
{
int fd;
struct input_event ie;
Display *dpy;
Window root, child;
int rootX, rootY, winX, winY;
unsigned int mask;
dpy = XOpenDisplay(NULL);
XQueryPointer(dpy,DefaultRootWindow(dpy),&root,&child,
&rootX,&rootY,&winX,&winY,&mask);
if((fd = open(MOUSEFILE, O_RDONLY)) == -1) {
perror("opening device");
exit(EXIT_FAILURE);
}
while(read(fd, &ie, sizeof(struct input_event))) {
if (ie.type == 2) {
if (ie.code == 0) { rootX += ie.value; }
else if (ie.code == 1) { rootY += ie.value; }
printf("time%ld.%06ld\tx %d\ty %d\n",
ie.time.tv_sec, ie.time.tv_usec, rootX, rootY);
} else if (ie.type == 1) {
if (ie.code == 272 ) {
printf("Mouse button ");
if (ie.value == 0)
printf("released!!\n");
if (ie.value == 1)
printf("pressed!!\n");
} else {
printf("time %ld.%06ld\ttype %d\tcode %d\tvalue %d\n",
ie.time.tv_sec, ie.time.tv_usec, ie.type, ie.code, ie.value);
}
}
return 0;
}

Answer 2

A mouse only sends relative movement, not absolute position. You have to keep track of it yourself, and when you receive a mouse-button event you have to check your own coordinates for the position.