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On 1/21/23 21:00 Paul Hahn wrote:
I think the OP's problem (which he's since
corrected) is probably one of assuming
a font had already been set, as I *think* what he's
saying is he called the getter
version of fl_font(), e.g. "fl_font(void)",
without having first called fl_font(face,size)
to set it,
which probably would have yielded "undefined
behavior".
Yes that is my case.
This has always been wrong, because measuring text w/o explicitly
setting the font would access undefined font data. An FLTK convention
is to use a font after setting it (which is fast if it has been done
at least once before) and leaving the font as-is. Hence even during
runtime you must always set the font you want to work with because
you would otherwise use the font used before which could for
instance be a bold italic 36 pix font.
It's certainly a valid use (and documented) to call
fl_font() outside of draw(),
such as to measure text with fl_measure() during
widget construction, before graphics
has been initialized. I'm guessing fl_font(face,size)
checks if graphics has not yet been
initialized, and initializes it.. but fl_font(void)
does not (and perhaps shouldn't)
Yes exactly. My code was calling fl_font(void) without ever
calling fl_font(face,size) at all, assuming that the font
(and size) were initialized to some reliable "default"
within FLTK (i.e., in the Fl_Window class constructor).
Again, this happened when my text-oriented class was
instantiated as a member of my class derived from Fl_Window.
That text-oriented class calls fl_font() to set up sizes of
things - again, assuming a default font + size is good.
From now on, to be rigorous, I will no longer assume there
is such a thing as "default" font + size in FLTK, and that I
must initialize it.
To be precise (sorry for nitpicking): there *is* a default font and
size, but it is not initialized at program startup automatically.
There are chances that your program never uses the default font, so
why bother and load it?
However, at least in my case, if the
Fl_Window class constructor had indeed initialized all of this
to some kind of defaults (including opening the display?), my
code would have continued to sail smoothly on. But I
understand that if opening the display fails in the
constructor, about the only option is to throw an exception
for the sake of the programmer who can catch it if desired.
That said, before commit 4b945a308 (Nov 5, 2022) there was an
unwanted initialization of the graphics driver in the constructor of
Fl_Widget (and hence also Fl_Window) which was removed with the
mentioned commit. This was necessary for the hybrid X11/Wayland FLTK
platform on Unix/Linux, but this early initialization of the
graphics driver had been problematic anyway.
This *may* have hidden the problem to access uninitialized font data
in your program because it crashed now with the missing graphics
driver initialization.
On the other hand, maybe some other toolkits (Qt?) take
care of this kind of initialization issue in a global
initialization routine that programmers are required to call
at the start? Like as with Fl::lock() in FLTK when we need to
use MT and locks. Or, as it now appears, fl_open_display(),
which might essentially fill that role now in FLTK, so calling
it at the start of their program is what everyone should do as
boilerplate.
fl_open_display() is called internally in many places when needed,
e.g. Fl_Window::show() but also Fl::font(face, size),
Fl::get_system_colors() and some (many) more functions. The rule is
not to call it if it's not needed (as in fluid in command mode `-c`)
but if you're sure your program needs it because it's a GUI program,
then it's not wrong to call it at the start of main(). Our goal is
to open the display only when necessary and that's usually when
Fl_Window::show(...) is called.
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