dynamically sizing the scroll region of a canvas widget

[Lee F Bernhard]

> Why don't you reconfigure the scrollregion of the canvas --
> After adding data just give
> $sc.fr2.c configure -scrollregion [$sc.fr2.c bbox all]
> This should work. I am also using the same technique in one of my apps.

You'll probably want to do the reconfiguration each time that the user
resizes the window. You can do this by creating a binding to the
<Configure> event for the canvas:

bind $sc.fr2.c <Configure> {
$sc.fr2.c configure -scrollregion [$sc.fr2.c bbox all]
}

The book Effective Tcl/Tk Programming (McLennan, Harrison) has a nice
section about creating resizeable canvases:

http://www.scriptics.com/resource/doc/books

We use that section in our Effective Tcl/Tk Programming course at
Scriptics.

Hope this helps,
Lee

______________________________________________________
Lee F. Bernhard lee.be...@scriptics.com
phone: (650) 843-6914 fax: (650) 843-6909
Scriptics Corporation http://www.scriptics.com

The Tcl Platform Company

[james_de...@ansett.com.au]

I am trying to set a dynamic size canvas, but I can't seem to do it.
I have tried the following:

canvas $sc.fr2.c -relief sunken -width 500 -height 300 -bd 2 \
-yscrollcommand "$sc.fr2.scroll set" -scrollregion {0 0 0 $rows} \
-confine true -yscrollincrement 25 -bg white

This has a problem with the variable $rows. Is it possible to do something
like this, maybe utilising "eval"? I need to keep it dynamic, as I don't
know how much data I will be trying to display.

Thanks for any help,

James.

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[Moinak Ghosh]

>
>canvas $sc.fr2.c -relief sunken -width 500 -height 300 -bd 2 \
>  -yscrollcommand "$sc.fr2.scroll set" -scrollregion {0 0 0 $rows} \
>  -confine true -yscrollincrement 25 -bg white
>
>This has a problem with the variable $rows.  Is it possible to do something
>like this, maybe utilising "eval"?  I need to keep it dynamic, as I don't
>know how much data I will be trying to display.
>

Why don't you reconfigure the scrollregion of the canvas --

After adding data just give
$sc.fr2.c configure -scrollregion [$sc.fr2.c bbox all]
This should work. I am also using the same technique in one of my apps.

Moinak.

[Eric Galluzzo]

james_de...@ansett.com.au wrote:

> I am trying to set a dynamic size canvas, but I can't seem to do it.
> I have tried the following:
>

> canvas $sc.fr2.c -relief sunken -width 500 -height 300 -bd 2 \
> -yscrollcommand "$sc.fr2.scroll set" -scrollregion {0 0 0 $rows} \
> -confine true -yscrollincrement 25 -bg white
>

> This has a problem with the variable $rows. [snip]

Presumably Tcl is giving you an error, something like "expected an integer but
got '$rows'". What you want is -scrollregion [list 0 0 0 $rows] instead of
-scrollregion {0 0 0 $rows}. This is because braces ({}) in Tcl always treat
their contents literally, so one of the coordinates in your scroll region is
the literal string "$rows".

- Eric

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[Victor Wagner]

james_de...@ansett.com.au wrote:
: I am trying to set a dynamic size canvas, but I can't seem to do it.
: I have tried the following:

: canvas $sc.fr2.c -relief sunken -width 500 -height 300 -bd 2 \
: -yscrollcommand "$sc.fr2.scroll set" -scrollregion {0 0 0 $rows} \
: -confine true -yscrollincrement 25 -bg white

: This has a problem with the variable $rows. Is it possible to do something

: like this, maybe utilising "eval"? I need to keep it dynamic, as I don't
: know how much data I will be trying to display.

You need to say
[list 0 0 $cols $rows]

I'm afrayd that saying scrollwidth to 0 is not a good idea. I've
experienced very interesting behavoir of canvas if it got
one-point long line or something simular. May be just setting
scrollwidth to window width

[list 0 0 500 $rows]

BTW name rows suggests that its value isn't expressed in pixels. May be
you have mean
[list 0 0 500 [expr $rows*$rowheight]]
?

: Thanks for any help,

: James.

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