event problem

[Carsten Haitzler]

On Sun, 29 Oct 2017 00:29:21 +0800 "石仔" <406643764 at qq.com> said:

> hi all.
> This is my ~/.xinitrc :
>               exec xterm
> 
> I start x with 'startx' command,  and then run 'testx'. This is  source :
> /* gcc testx.c -o testx -lX11 */
>   1 #include <stdio.h>
>   2 #include <X11/Xlib.h>
>   3 int main(int argc, char *argv[])
>   4 {
>   5 
>   6     Display *display=XOpenDisplay(NULL);
>   7     Window root, parent, *child=NULL, root_win=RootWindow(display,
> DefaultScreen(display)); 8     unsigned int n;
>   9     XWindowAttributes attr;
>  10     if(XQueryTree(display, root_win, &root, &parent, &child, &n))
>  11         for(size_t i=0; i<n; i++)
>  12             if(XGetWindowAttributes(display, child[i], &attr)
>  13                 && attr.map_state == IsViewable
>  14                 && XSelectInput(display, child[i], ButtonPressMask))
>  15                     printf("set %x\n", child[i]);
>  16     XEvent event;
>  17     while(1)
>  18     {
>  19         XNextEvent(display, &event);
>  20         if(event.type == ButtonPress)
>  21         printf("type=%d, w=%x\n", event.type, event.xbutton.window);
>  22     }
>  23 }
> 
> I can not get ButtonPress when i press button. But I can get EnterNotify if i
> replace ButtonPressMask with EnterWindowMask. why ?

Because another client (xterm itself) is listening for button presses. presses
(and releases) only go to the first client to request them on a window because
of implicit grabs. You can try intercept them via parent windows (XGrabButton
+ XAllowEvent fun) which is how window managers do click to focus. Only 1
client can select for button press/release events on a window.

-- 
------------- Codito, ergo sum - "I code, therefore I am" --------------
Carsten Haitzler - raster at rasterman.com