I have a canvas with a chart, a bar chart, and a grid background. Or maybe
that is more accurately described as a canvas with a grid and a bar chart
on top of it. It seems to me that whatever is drawn last becomes "on top"
of everything else.

And there is a "floating" canvas label that displays some data in a much more
evident way.

I have managed to make that chart "scrollable" left and right. I use the arrow
keys for that. But when I scrolled, the floating label would be pushed off the
right edge of the screen. I fixed that:

proc scrollchart {leftright} {
lassign [$::chart xview] x1 x2
if {$leftright == "left"} {
$::chart xview moveto [expr $x1 - 0.0005]
set ::toplabel_x [expr $::toplabel_x - 10]
}
if {$leftright == "right"} {
$::chart xview moveto [expr $x1 + 0.0005]
set ::toplabel_x [expr $::toplabel_x + 10]
}

That works very well. The label flickers a little, but it stays put.

But there is also this:

bind $::chart <B1-Motion> {%W scan dragto %x %y 1}

That works to the extent that I can indeed drag the chart left and right
with the mouse pointer, but then the floating label gets dragged too, which
I obviously don't want.

Maybe there is some code I could use to compensate for the movement like I did
in the scrollchart proc, but then I think, everything would be so much easier
if I could anchor some elements to some edge or corner of the visible screen
rather than to the canvas' hard coordinates.

I am struggling with that concept. Can someone please shed some light?

--
Luc
>>

* Luc <no@no.no>
| I have a canvas with a chart, a bar chart, and a grid background. Or maybe
| that is more accurately described as a canvas with a grid and a bar chart
| on top of it. It seems to me that whatever is drawn last becomes "on top"
| of everything else.
>
| And there is a "floating" canvas label that displays some data in a
| much more evident way.
>
| I have managed to make that chart "scrollable" left and right. I use the arrow
| keys for that. But when I scrolled, the floating label would be pushed off the
| right edge of the screen.
--<snip-snip>--
| That works to the extent that I can indeed drag the chart left and right
| with the mouse pointer, but then the floating label gets dragged too, which
| I obviously don't want.

Rather than trying to compensate for the canvas scrolling, place the
'floating' label in a separate canvas and [place] that one in the
original canvas?

canvas .c1 ; # the scrolled canvas
canvas .c1.c2 ; # the one with the floating label
place .c1.c2 -relx 0 -rely 0 ; # always top left in .c1

R'

On Tue, 15 Nov 2022 16:36:54 +0100, Ralf Fassel wrote:

> Rather than trying to compensate for the canvas scrolling, place the
> 'floating' label in a separate canvas and [place] that one in the
> original canvas?
>
> canvas .c1 ; # the scrolled canvas
> canvas .c1.c2 ; # the one with the floating label
> place .c1.c2 -relx 0 -rely 0 ; # always top left in .c1
>
> R'

Thanks.

That works in terms of positioning, but then the floating canvas eclipses
the background grid. Sadly, there is no transparent canvas in Tk.

--
Luc
>>

Le 16/11/2022 à 00:52, Luc a écrit :
> On Tue, 15 Nov 2022 16:36:54 +0100, Ralf Fassel wrote:
>
>> Rather than trying to compensate for the canvas scrolling, place the
>> 'floating' label in a separate canvas and [place] that one in the
>> original canvas?
>>
>> canvas .c1 ; # the scrolled canvas
>> canvas .c1.c2 ; # the one with the floating label
>> place .c1.c2 -relx 0 -rely 0 ; # always top left in .c1
>>
>> R'
>
>
> Thanks.
>
> That works in terms of positioning, but then the floating canvas eclipses
> the background grid. Sadly, there is no transparent canvas in Tk.
>
>

Hello, but there is "transparent" toplevel in which you could pack the
canvas and then use the transparent color in canvas background. Then
place the transparent toplevel where you wish to.

--
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* Adrien Peulvast <adrien.peulvast@hotmail.com>
| Le 16/11/2022 à 00:52, Luc a écrit :
| > Thanks.
| > That works in terms of positioning, but then the floating canvas
| > eclipses the background grid. Sadly, there is no transparent canvas in Tk.
| >
>
| Hello, but there is "transparent" toplevel in which you could pack the
| canvas and then use the transparent color in canvas background.

What is the "transparent color" for the canvas? Could you show the
-configure line?

R'