PerlTk - Bind Mouse event to canvas background?

Author

Bind Mouse event to canvas background?

Josef Moellers

2005-09-29, 7:56 am

Hi,

I'd like to bind a mouse button press to a canvas.
I tried
#! /usr/bin/perl

use warnings;
use strict;
use Tk;

sub MeldeDich {
print STDERR join(" ", @_), "\n";
}
# Create main window.
my $main =3D new MainWindow;

my $canvas =3D $main->Canvas(
-height =3D> "12c",
-width =3D> "16c",
-background =3D> "blue",
);
$canvas->pack(-side=3D>"top", -fill=3D>"x");
$canvas->bind($canvas, '<Button-1>', [ \&MedleDich, "Hello\n" ]);
$canvas->bind($canvas, '<Button-1>', [ \&MedleDich, "Hello\n" ]);
MainLoop;

but I get no output ...

In the end, I'd like to know where on the canvas I have pressed the=20
mouse button (I'd like to select a region of a graph for zooming).

Josef
--=20
Josef M=F6llers (Pinguinpfleger bei FSC)
If failure had no penalty success would not be a prize
-- T. Pratchett

Barry

2005-09-29, 7:56 am

"Josef Moellers" <josef.moellers@fujitsu-siemens.com> wrote in message
news:dhgb59$v1j$1@nntp.fujitsu-siemens.com...
Hi,

I'd like to bind a mouse button press to a canvas.
I tried
#! /usr/bin/perl

use warnings;
use strict;
use Tk;

sub MeldeDich {
print STDERR join(" ", @_), "\n";
}
# Create main window.
my $main = new MainWindow;

my $canvas = $main->Canvas(
-height => "12c",
-width => "16c",
-background => "blue",
);
$canvas->pack(-side=>"top", -fill=>"x");
$canvas->bind($canvas, '<Button-1>', [ \&MedleDich, "Hello\n" ]);
$canvas->bind($canvas, '<Button-1>', [ \&MedleDich, "Hello\n" ]);
MainLoop;

but I get no output ...

In the end, I'd like to know where on the canvas I have pressed the
mouse button (I'd like to select a region of a graph for zooming).

Josef
--
Josef Möllers (Pinguinpfleger bei FSC)
If failure had no penalty success would not be a prize
-- T. Pratchett

Try:
use warnings;
use strict;
use Tk;

sub MeldeDich {
print STDERR join(" ", @_), "\n";
}

# Create main window.
my $main = new MainWindow;

my $canvas = $main->Canvas(
-height => "12c",
-width => "16c",
-background => "blue",
);
$canvas->pack(-side=>"top", -fill=>"x");
$main->bind($canvas, '<Button-1>', [ \&MeldeDich, "Hello\n" ]);
MainLoop;

Barry

Josef Moellers

2005-09-29, 7:56 am

Barry wrote:

> $main->bind($canvas, '<Button-1>', [ \&MeldeDich, "Hello\n" ]);
(rather than my $canvas->bind($canvas, ...)

Thanks, this now works.

--=20
Josef M=F6llers (Pinguinpfleger bei FSC)
If failure had no penalty success would not be a prize
-- T. Pratchett

Konstantin Tokar

2005-09-29, 6:58 pm

Josef Moellers wrote:
> Hi,
>
> I'd like to bind a mouse button press to a canvas.

[O'Reilly , "Mastering Perl/Tk" by Steve Lidie and Nancy Walsh]

9.4. Using bind with a Canvas

When you try to use the bind method with a Canvas widget, you can easily
run into unexpected problems. You may either get an error and your
script won't run, or your script will run but your bind won't seem to
have any effect. What's happening here is that Canvas objects have their
own special bind method that works with tags and item IDs. To get around
this, you'll need to use CanvasBind, a special method that binds events
to the canvas as a whole:

$canvas = $mw->Canvas( );
$canvas->CanvasBind("<Button-1>", sub { print "bind!\n"; });

If you used the Scrolled method to create your Canvas, you'll have an
added difficulty; you'll have to use the Subwidget method to get to the
Canvas widget:

$canvas = $mw->Scrolled("Canvas");
$real_canvas = $canvas->Subwidget("canvas");
$real_canvas->CanvasBind("<Button-1>", sub { print "bind!\n" });

Other than this one small annoyance, bind works just as you would
expect. This example prints the Canvas coordinate you clicked on:

$c = $mw->Scrolled("Canvas")->pack( );
$canvas = $c->Subwidget("canvas");
$canvas->CanvasBind("<Button-1>", [ \&print_xy, Ev('x'), Ev('y') ]);
sub print_xy {
my ($canv, $x, $y) = @_;
print "(x,y) = ", $canv->canvasx($x), ", ", $canv->canvasy($y), "\n";
}

To summarize, use bind to create event bindings to Canvas items, and use
CanvasBind to create event bindings to the Canvas widget.

Ala Qumsieh

2005-09-29, 6:58 pm

Josef Moellers wrote:

> $canvas->bind($canvas, '<Button-1>', [ \&MedleDich, "Hello\n" ]);

Here, you are calling Tk::Canvas::bind. What you need is
Tk::Canvas::CanvasBind (which is just an alias to Tk::bind):

$canvas->CanvasBind('<Button-1>', ...);

or equivalently:

$canvas->Tk::bind('<Button-1>', ...);

> In the end, I'd like to know where on the canvas I have pressed the
> mouse button (I'd like to select a region of a graph for zooming).

I've written an article about this very subject:

http://www.perltk.org/index.php?opt...id=13&Itemid=28

--Ala

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