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On 4/28/24 20:18 Gonzalo Garramuño wrote:
On 28/4/24 12:13, 'Albrecht Schlosser' via fltk.coredev wrote:
OK, thanks for confirmation. Can you try my patch (code above) ?
Tried it. Seems to fix Windows, Wayland and XWayland (did not try
macOS and X11 yet but I am guessing they should be fine too).
Thanks for testing it. It's basically your "patch" with minor
modifications.
I'll give it another review tomorrow and I will very likely commit
it. I'm pretty sure that the patch itself is correct but I still
don't understand everything that leads to this situation. Your
example code is a good reproducer and was very helpful in analyzing
the issue (more to come tomorrow).
One bug of your program (and I call it a bug because it causes a
kind of undefined behavior) can be seen in a comment in your example
code:
Timeline(int X, int Y, int W, int H, const char* L = 0) : Fl_Gl_Window(X, Y, W, H, L) { //Fl_Group::current(0); // adding this seems to make it not crash [1] thumbnailWindow = new Fl_Double_Window(120, Y - 100, 128, 80); [2] thumbnailWindow->clear_border(); thumbnailWindow->set_non_modal(); [3] thumbnailWindow->begin();
Fl_Box* box = new Fl_Box(2, 2, 120 - 2, 80 - 2); box->box(FL_FLAT_BOX); box->color(FL_BLACK); thumbnailWindow->end(); [4] end(); [5] }
[1] You should really enable this statement to make sure
that `thumbnailWindow` does not become a child (subwindow) of
the Timeline (Fl_Gl_)Window.
[2] Since the constructor of Fl_Gl_Window ends
with `begin();` as all group widgets do the following `thumbnailWindow`
will become a child if you don't enable the statement above.
Alternative code after the c'tor of thumbnailWindow:
if (parent()) parent()->remove(this);
but this is IMHO the less elegant solution.
[3] set_non_modal() should only be used on top-level windows
and makes the window stay above its base window (in Z order). In FLTK this relation is determined when
the modal or non-modal window is shown: the active window becomes
its base (or "parent") window as far as the system is concerned.
Unfortunately we can't affect this order by any other means.
[4] This is correct but superfluous, because it is followed by `end();` [5]
[5] This end()'s the `Timeline`
window which does not really do what everybody expects. What it
really does is Fl_Group::current([this->]parent()), i.e. it makes the parent of the Timeline
widget the new "current group". In your code environment (in the
test program) this would be correct if ... you didn't enable the
statement in [1]. Therefore you would have to use `win.begin()` in
your main program if you intended to add other widgets after the
timeline. This is not the case in your demo program but may well
be in your real program.
As you wrote yourself "adding this seems to make it not crash", and
as I wrote above, this would be better because it prevents making
the "non-modal" `thumbnailWindow` a subwindow of
your main window. I'm not sure if it is documented that subwindows
and { modal | non-modal } are mutually exclusive (IMHO this must be
the case).
However, there are still some things I do not yet fully understand
when it comes to event delivery of FL_LEAVE events and hiding the
non-modal subwindow. In my tests I could only trigger the NULL
pointer dereference (the patched code in Fl_Window) when I dragged
the mouse (timeline) to the right out of the window. It does not
happen when the mouse leaves the timeline to any other direction
(up, down, and including to the left side). But that is internal
stuff and should not affect you and your program.
Summary:
(1) You should fix your program (see above) and ...
(2) I will fix the potential NULL pointer dereference.
Good night from here
Albrecht
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