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[STR New]

Link: http://www.fltk.org/str.php?L2232
Version: 1.3-current


I'm seeing a problem with the low-level keyboard handling in both
FLTK1 and FLTK2. If using a program that artificially generates
X11 keystrokes to type any word with non-consecutive, repeated
letters into an FLTK app, FLTK transposes the letters. An example
of such a keystroke-generating application is a soft keyboard,
such as those used on touchscreen phones. A keyboard that uses a
dictionary to type a word-at-a-time types the letters in a quick
succession, triggering this bug. I'm attaching 2 test programs to
demonstrate the issue, one in C and another in Perl. Both use
XTest to type "morning" (assuming a "standard" keyboard). This
works fine when typing into an app not built with FLTK, but FLTK
often produces "mornnig" instead. This is sensitive to timing, so
the bug doesn't occur 100% of the time, but quite often on my
computer.

The cause of the issue is code in FLTK to handle key
repeats. When a key is held down, X sends repeated press and
release events. FLTK fights this by looking into the X event
queue to detect this condition, and to pull out press events to
process them earlier. Thus, the second "n" in "morning" moves up
in the queue to produce the error. In FLTK1, this behavior was
introduced in revision 2937 (this revision has no other
changes). In FLTK2, almost-identical behavior was introduced in
revision 2944.

I must admit I don't understand why FLTK doesn't want to handle
repeated press and release events that X generates. A quick test
with that code pulled out didn't reveal any breakage, but I
didn't try for very long. We can pull out this code permanently
if the issue no longer exists (the code was written in
2003). Otherwise, we can make fake_keyup_test() smarter by
preventing it from triggering if different keys are seen in the
queue in-between the repeating keys.


Link: http://www.fltk.org/str.php?L2232
Version: 1.3-current

Attachment: type_morning.pl
Description: Binary data

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