How can I simulate a drag action using Xlib? - c++

Question

I have an application which uses Xlib library for simulate a mouse on the screen.
I used XQueryPointer and XWarpPointer functions with which I can simulate a mouse movement and also a click. My problem is that I can't "drag" an element (it's an interface with some blocks which you can move within a Qt application written in C++ and launched on Ubuntu).
I use many parts of this extract:
Sending X11 click event doesn't work with some windows
Can this function help me?
::XGrabPointer(mDisplay, window, True,
ButtonPressMask |
ButtonReleaseMask |
PointerMotionMask |
FocusChangeMask |
EnterWindowMask |
LeaveWindowMask,
GrabModeAsync,
GrabModeAsync,
RootWindow(mDisplay, DefaultScreen(mDisplay)),
None,
CurrentTime);
Do you have any idea?
Thank you in advance.

Answer 1

If you're okay with spawning a child process, you can easily use xdotool for this, as in:
xdotool mousedown 1
sleep 0.5
xdotool mousemove_relative --sync 200 200
sleep 0.5
xdotool mouseup 1
http://www.semicomplete.com/projects/xdotool/
http://tuxradar.com/content/xdotool-script-your-mouse
The source code to xdotool would serve as a good starting point if you want to do this yourself in C with the XTest library.

Answer 2

You can achieve this by sending the XMotionEvent to the window. the way X11 know that it is a drag event is by checking the state. So, if the state is OR with the Button1Mask then it means that the Motion is done when the Button1 was pressed.
I am pasting the pseudo code here. You might want to populate the relevant fields of the XMotionEvent as per your use-case.
Display *OpenedDisplay = XOpenDisplay(NULL);
int ret = 0,screen = 0;
XMotionEvent xbpe;
Window dummy;
unsigned int mask,dummyUInt;
int dummyInt;
int screencount = ScreenCount(xbpe.display);
for (int i = 0; i < screencount; i++) {
Screen *screenPointer = ScreenOfDisplay(xbpe.display, i);
ret = XQueryPointer(xbpe.display, RootWindowOfScreen(screenPointer), &dummy, &dummy,
&dummyInt, &dummyInt, &dummyInt, &dummyInt, &mask);
if (ret == True) {
screen = i;
break;
}
}
xbpe.type = MotionNotify;
xbpe.display = OpenedDisplay;
xbpe.window = wid;
xbpe.root = RootWindow(xbpe.display, screen);
xbpe.subwindow = None;
xbpe.time = CurrentTime;
xbpe.x = src_x;
xbpe.y = src_y;
xbpe.state = mask;
xbpe.is_hint = NotifyNormal;
xbpe.same_screen = True; /* Should we detect if window is on the same screen as cursor? */
XWindowAttributes attr;
ret = XGetWindowAttributes(xbpe.display, wid, &attr);
if(ret == 0){
qDebug() << wid <<"XGetWindowAttributes unsuccessfull returning early";
return;
}
/**************************** This is key here *******************/
if(isDrag){
xbpe.state |= Button1Mask;
}
ret = XSendEvent(xbpe.display, wid, False, PointerMotionMask|ButtonMotionMask|MotionNotify, (XEvent *)&xbpe);
XFlush(OpenedDisplay);
XCloseDisplay(OpenedDisplay);
I would recommend navigating the source code of xdotool. It doesn't specifically covers your issue but gives you enough information on populating the fields of X*Event.