[MACTCL] Bug in text widget <MouseWheel> binding.

[Neil M. <ne...@cs...>]

I was just playing with a text widget and scrollbar on Tcl/Tk Aqua, and 
it seems that the scroll-wheel implementation is partially broken. Is 
this a known bug? Basically, I can use the mouse wheel to scroll down 
the widget, but not up. A small test script which demonstrates the 
problem:

pack [scrollbar .vsb -orient vertical -command [list .t yview]] -side 
right -fill y
pack [text .t -yscrollcommand [list .vsb set]] -fill both -expand 1
for {set i 0} {$i < 100} {incr i} { .t insert end "$i\n" }

Now when you use the mouse wheel, you can scroll down, but not up. This 
is using the wish 8.4.5 from the recent TclTkAquaBI distro.

... A little more digging, and I think I've found the cause. The Text 
class has the following binding for <MouseWheel>:

   %W yview scroll [expr {- (%D / 120) * 4}] units

Now, scrolling the wheel up gives delta values between 1 and 21 (for 
me), whereas down it gives -1 to -21. Using the expr given, 21/120 == 0 
(integer arith, round down), whereas -21/120 == -1.

I presume this binding is specific to Mac OS X, as I've never had a 
problem with the mouse wheel on Windows or Linux (although on *nix the 
bindings are to Button-4/5). Anyway, as I can't get delta values above 
120 (or anywhere near it), this expr is never going to work. Does 
anyone get large values for delta on Mac OS X? If not, I suggest 
changing the binding to something more like:

%W yview scroll [expr { - round(%D/5.0)}] units

which seems to work ok for me (note the use of round()).

If this is a new bug, should I submit it somewhere? Do Mac OS X Tk bugs 
get tracked at the usual Tk bug tracker, or in a separate project?

Cheers,

Neil.