Tk Source Code

Tk8.5 introduces a new subcommand to grid called 
"anchor". This subcommand controls the placing of
grids which are smaller than its containing widget.
Unfortunately the default behaviour is set to
"nw" while in Tk8.4 (where you couldn't specify
the anchor) it was "center".

This leads to some broken layouts, like 
iwidgets disjointlistbox with "-buttonplacement center".

A short Tk-only example for demonstration:

<tcl>
frame .f -background blue
button .f.b1 -text "Button 1"
button .f.b2 -text "Button 2"

# uncomment next line for 8.5 compatiblity
#grid anchor .f center
grid .f.b1
grid .f.b2

pack .f -fill both -expand true
wm geometry . =200x800
</tcl>

Running this, you will see the buttons are in the
center using 8.4 and in the upper left corner 
using 8.5. For the latter the "grid anchor" line 
is necessary to yield the same result (but isn't
backward compatible).

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Re-reading TIP #146 I see the point.
So what about an anchor called "classic", which
implements the old (inconsistent) behaviour?
And, of course, this becomes the default 
behaviour, or is set as such by 
tk::classic::restore.

Just a thought...

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Note that having "center" as default is not fully
backward compatible either, as discussed in the TIP.
So I'd feel uncomfortable putting anything about this
in [tk::classic::restore].

The trivial, backward compatible, fix can be applied by anyone
affected. Noting it here for reference:
catch {grid anchor $w center}

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patch from Uwe for iwidgets noted in http://groups.google.com/group/comp.lang.tcl/browse_thread/thread/86590035a1030c71/468f247140e6059f?hl=en#468f247140e6059f applied to iwidgets.

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Any chance that [tk::classic::restore]
addresses this?