Xlib mouse events and ButtonPressMask

abhinav.zoso · 11-26-2009, 11:56 PM

I have written a simple program which will report key press and release events for a particular window. In my case, it is mostly the terminal since I invoke the program from the terminal. I am able to get the key press and release events taking place in the terminal window (I have used XSelectInput() with KeyPressMask and KeyReleaseMask on the terminal) but the same is not working with ButtonPress and ButtonRelease. Not just these, but any events related to the mouse are not being reported. Any idea why this is happening?

Code:

#include
#include
#include
#include
#include
#include

int main() {
Display *display = XOpenDisplay(NULL);
KeySym k;
int revert_to;
Window window;
XEvent event;

XGetInputFocus(display, &window, &revert_to);
XSelectInput(display, window, KeyPressMask | KeyReleaseMask | ButtonPressMask | ButtonReleaseMask);

while(1)
{
XNextEvent(display,&event);
switch (event.type) {

case KeyPress : printf("Key Pressed\n"); break;
case KeyRelease : printf("Key Released\n"); break;
case ButtonPress : printf("Button Pressed\n"); break;
case ButtonRelease : printf("Button Released\n"); break;
case EnterNotify : printf("Enter\n"); break;
}
}
XCloseDisplay(display);
return 0;
}

mknirsch · 11-27-2009, 06:16 AM

The mouse (pointer) generates events when it moves, when it crosses window borders and when buttons are pressed.

When one wants to obtain the final pointer position XQueryPointer() is a good function to call.

ButtonPress and ButtonRelease events are fired when the pointer buttons are presses and released. A mouse (pointing device) can have many buttons, these buttons are mapped on a bit mask that can be changed by XSetPointerMapping(); one can read this mapping by the XGetPointerMapping() function call.

The System automatically grabs the pointer between the ButtonPress and ButtonRelease events and presents it to the client window where the button was pressed. So the client always receives two button events (press, release). Only one client can select this button events.

The distribution of the ButtonRelease events can be controlled by XSelectInput calls where one can select OwnerGrabButtonMask. This will cause the ButtonRelease event to be send to the same application where the presses event took place.

main()
...
XEvent event;
unsigned int button;
...
display = XOpenDisplay(...
screen = DefaultScreen( display...
...
XSelectInput(display, RootWindow(display, screen), ButtonPressMask | ButtonReleaseMask | ExpousureMask,
...
gc = XCreateGC( display
...
while(1)
{
XNextEvent(display, &event) // trap any event
switch( event.type)
case ButtonPress:
button = event.xbutton.button;
while(1)
{
...XCheckTypedEvent(display, ButtonPress, event)
// process other button pressed events..
XMskEvent(display ButtonReleaseMask, &event)
if( event.xbutton.button == button)
// process released event
}
case...
...
}

For details please also take a look into O'Reilly's XLib Programming Manual. Here you can find a detailed description with some examples.
Good luck
Martin