How to read low level mouse click position in linux .

c++ linux mouse

17,153

Solution 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;
}

Solution 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.

17,153

rajat

Updated on July 14, 2022

Comments

rajat almost 2 years

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 .

rajat almost 12 years

Hi ,The code seems very elegant .Thanks . But it is giving me following errors :1. undefined reference to XOpenDisplay , 2. undefined reference to XQueryPointer .
perreal almost 12 years

you need to compile with X11 lib: gcc main.c -lX11.
rajat almost 12 years

Yup , it worked :) . But the co-ordinates are messed up , the 0,0 point is somewhere in between of the screen.
rajat almost 12 years

I understood the problem , when i go to the corners of the screen the mouse is not able to move but it still keeps on increasing the value of the mmouse co-ordinates . what are the Possible solutions ?
perreal almost 12 years

You can use XQueryPointer when you need absolute coordinates instead of tracking the pointer.
rajat almost 12 years

How to differentiate between mouse up and down events , using the low level thing , the code that appear for both mouse down and mouse up is same . if i want to detect the co-ordinates only when the mouse button is pressed , what should i do ?
perreal almost 12 years

@rajat, added an example for buttons in the code. hope it helps
Matical almost 9 years

how to do this in android?