TK Canvas: Group vs. tags

[dreadpiratepeter]

I've been doing a little TK work lately, and I was looking through my Emu book. I noticed that there is a new canvas item called Group, that collects other items and allows you to act on them as a unit.
Traditionally, I would just tag all the items with a unique tag and use it to act on the items.
So my question is: Is the Group type just syntactic sugar? Or are there performance and/or memory benefits to using groups?

[zentara]

I'm not sure about the standard Tk Canvas 'group', but in Tk::Zinc( an enhanced canvas ) , groups are very important in doing things like rotations and motion. Maybe this would be a good question for comp.lang.perl.tk where those experts can explain the c code behind it all.

For instance, if you tried to rotate a bunch of "tags", they would all rotate independently; but if they are grouped, you can specify the group center point, where they would rotate around.

[zentara]

As an example of the usefulness of using groups in motion operations, show me how you would do this with just 'tags'.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = MainWindow->new();

# first create a canvas widget 
my $canvas = $mw->Canvas(width => 300, height => 200)->pack();
my $one = $canvas->createOval(5,  0, 20, 30, -fill => 'blue');
my $two = $canvas->createRectangle(0, 20, 50, 75, -fill => 'red');

my $group = $canvas->createGroup([0, 0], -members => [$one, $two]);

my $dx = 1;
my $dy = 1;
my $id = Tk::After->new($canvas,10,'repeat',
             sub {$canvas->move($group, $dx,$dy);
                 my ($x,$y) = $canvas->bbox($group);
                 print "$x $y\n";
                 if($y >= 100){$dy = -1};
                 if($x >= 200){$dy = 1; $dx = -1};
                 if($x < -5){$dx=1;$dy=1};
          });

my $ebutton = $mw->Button(-text => 'Exit',
                  -command => 'Tk::exit')->pack();

my $sbutton = $mw->Button(-text => 'Stop',
                  -command => sub{$id->cancel;})->pack();


MainLoop();

[dreadpiratepeter]

Like this:

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = MainWindow->new();

# first create a canvas widget 
my $canvas = $mw->Canvas(width => 300, height => 200)->pack();
my $one = $canvas->createOval(5,  0, 20, 30, -fill => 'blue',-tags => 
+['fred']);
my $two = $canvas->createRectangle(0, 20, 50, 75, -fill => 'red',-tags
+ => ['fred']);

#my $group = $canvas->createGroup([0, 0], -members => [$one, $two]);
my $group='fred';
my $dx = 1;
my $dy = 1;
my $id = Tk::After->new($canvas,10,'repeat',
             sub {$canvas->move($group, $dx,$dy);
                 my ($x,$y) = $canvas->bbox($group);
                 print "$x $y\n";
                 if($y >= 100){$dy = -1};
                 if($x >= 200){$dy = 1; $dx = -1};
                 if($x < -5){$dx=1;$dy=1};
          });

my $ebutton = $mw->Button(-text => 'Exit',
                  -command => 'Tk::exit')->pack();

my $sbutton = $mw->Button(-text => 'Stop',
                  -command => sub{$id->cancel;})->pack();


MainLoop();

Update: Actually I can see the usefulness for rotation. But for motion, and state-changes and such the two methods appear the same.

[zentara]

Well, I'm out of XP today, but I would give you one for that. :-)