Does a Gtk application window have a callback for mouse movement?

Question

I'm just playing around with Gtk, deciding whether I should spend time learning it. I have an application window with an "activate" callback, which gets called. After that callback returns, and the window is present on the screen, if I move the mouse, I get a "division-by-zero" error. I don't have a mouse movement callback. If that's the problem, I should add one. But what is the name of the mouse movement callback? The only one I've found is "move-cursor", which seems to be for an editing cursor, not a mouse cursor.

I'm using /usr/lib/x86_64-linux-gnu/libgtk-3.so.0 because that's the one that happens to be on my Ubuntu PC. libgtk-3.so.0 is identical to libgtk-3.so.0.2200.25.

MCVE:

#!/usr/local/bin/sbcl --script

(define-alien-routine gtk_application_window_new (* t) (app (* t)))
(define-alien-routine gtk_application_new (* t) (txt c-string) (flags int))
(define-alien-routine g_application_run int
                      (app (* t)) (argc int) (argv (* t)))
(define-alien-routine g_signal_connect_data int;
                      (instance (* t)) (sig c-string)
                      (cback (function void (* t) int))
                      (data (* t)) (unusedptr (* t)) (unusedint int))
(define-alien-routine gtk_window_set_title void (win (* t)) (ttl (c-string)))
(define-alien-routine gtk_window_set_default_size void
                           (win (* t)) (x int) (y int))
(define-alien-routine gtk_widget_show_all void (win (* t)))

(sb-alien::define-alien-callback mycallback void ((app (* t)) (u int))
  (with-alien ((win (* t)))
    (setf win (gtk_application_window_new app))
    (gtk_window_set_title win "This")
    (gtk_window_set_default_size win 100 100)
    (gtk_widget_show_all win)))

(load-shared-object "/usr/lib/x86_64-linux-gnu/libgtk-3.so.0")
(with-alien ((app (* t)) (status int))
  (setf app (gtk_application_new nil 0))
  (g_signal_connect_data app "activate" mycallback nil nil 0)
  (g_application_run app 0 nil))

Give us guys an MCVE to observe. We have no idea what your code looks like. — theGtknerd
I should give it the mouse movement callback first, then make the MCVE from that. The only callback I presently give it is the "activate" callback. It calls that and shows the window. Then when it gets mouse movement is when it crashes with the division-by-zero error. — Mr E
If you don't know what I mean by a callback, I mean the function you give as an argument to g_signal_connect. The only callback I presently have is the "activate" callback, which gets called and returns. Then, with the window visible, waiting for input, I move the mouse, and it crashes. That seems to imply I need a mouse-movement callback. Right? — Mr E
Please show us some code first. We can't guess why you get a division by 0 error out of the blue. A simple app won't crash just because you didn't connect a callback to a signal. — liberforce
Please also add the result of pkg-config --modversion gtk+-3.0, so we know exactly the version you're using, as the so name is mostly useless. — liberforce

Mr E Mr E · Accepted Answer · 2018-12-19T16:03:51

A callback for mouse movement turned out not to be the issue.

The cause of the divide-by-zero error turned out to be that GTK relies on being able to divide by zero. All I had to do to fix it was to tell SBCL to not consider division by zero to be an error. The only reason mouse movement was involved was that the division by zero happens then. The reason why it doesn't happen in most other programming languages is that they don't consider division by zero to be an error.

To fix the MCVE script, to make it work, simply add this line after the shebang line, to tell it to only consider overflow and invalid to be floating point errors, and not division by zero: (sb-int:set-floating-point-modes :traps '(:overflow :invalid))

Does a Gtk application window have a callback for mouse movement?

1 Answers