Mouse clicks with one mouse pointer device without stealing focus

// Compile with: gcc -o test XSendEvent3.c -lX11
//https://tronche.com/gui/x/xlib/events/structures.html
//https://tronche.com/gui/x/xlib/events/keyboard-pointer/keyboard-pointer.html#XButtonEvent
//https://www.x.org/releases/X11R7.5/doc/man/man3/XKeyEvent.3.html
#include <X11/Xlib.h>

// Simulate mouse click
void click (Display *display, int button)
{
  // Create and setting up the event
  XEvent event;
  
  event.xbutton.button = button;
  event.xbutton.subwindow = DefaultRootWindow (display);
  
  while (event.xbutton.subwindow)
    {
      event.xbutton.window = event.xbutton.subwindow;
      XQueryPointer (display, event.xbutton.window,
		     &event.xbutton.root, &event.xbutton.subwindow,
		     &event.xbutton.x_root, &event.xbutton.y_root,
		     &event.xbutton.x, &event.xbutton.y,
		     &event.xbutton.state);
    }
    
  // Press
  event.type = ButtonPress;
  XSendEvent (display, PointerWindow, True, ButtonPressMask, &event);
  
  // Release
  event.type = ButtonRelease;
  XSendEvent (display, PointerWindow, True, ButtonReleaseMask, &event);
}

int main (int argc, char *argv[])
{
  Display *display = XOpenDisplay(0);
  click (display, Button1);
  XCloseDisplay(display);
}