[Tcl-bugs] [ tktoolkit-Bugs-2543460 ] Enter/Leave cnv events not reported while mouse btn is down

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Bugs item #2543460, was opened at 2009-01-28 18:11
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Category: 04. Canvas Basics
Group: current: 8.5.6
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: mescalinum (mescalinum)
Assigned to: Jeffrey Hobbs (hobbs)
Summary: Enter/Leave cnv events not reported while mouse btn is down

Initial Comment:
consider this little testcase:

pack [canvas .c -width 300 -height 190 -background white]
# two test items
.c create rectangle 20 30 40 50 -tags red -fill red
.c create rectangle 80 30 100 50 -tags black -fill black
# text items for showing what's happening
.c create text 20 90 -text {red: } -tags txt1 -anchor nw
.c create text 20 120 -text {tags: } -tags txt2 -anchor nw
# bind <Enter> and <Leave>
.c bind red <Enter> {.c itemconfigure txt1 -text red:\ Enter}
.c bind red <Leave> {.c itemconfigure txt1 -text red:\ Leave}
# the workaround: (this fails too)
bind .c <Motion> {.c itemconfigure txt2 -text tags:\ [.c gettags [.c find withtag current]]}
# not really needed for this testcase:
bind .c <ButtonPress> {.c configure -background red}
bind .c <ButtonRelease> {.c configure -background white}


item with 'red' tag is bound to <Enter> and <Leave> events.
but it works only when the bouse button are not pressed.
if you click in the white area and drag over the red item, it won't send the <Enter>/<Leave> events.

in addition, an attempt to workaround this issue by using [.canvas find withtag current&&$myTag] would fail too, because tag 'current' is not updated while mouse button is down.

I don't know if this is expected, or not.
reading the manual of canvas I'd expect 'current' tag and <Enter>/<Leave> events to work in any condition.

I'm not filing a bug about documentation though.
I'd rather want those things working (perhaps enabled by some exotic [canvas] option), because a full workaround on this issue implies various nested loops, to track position and retrieve all the tags,  and match them, and other than awful, I think it could turn into a performance hog.

Best regards

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