Sorry, Master,

I have to disagree with you on this one :-)

After working on it for a while, I got what seems to be a feasible solution.  It took a little extra work to get it to function for zoom-in and zoom-out, but here's how to do it:

First, near the top of your program with the other global variable declarations, add two variables, an array @box and a scalar $viewable_width:

my @box;                 # Tracks the IDs of each rectangle
my $viewable_width=400;  # How wide is the viewable Canvas?
[download]

You may also want to use $viewable_width when constructing the Canvas:

    $sc[$i] = $tile[$i]->Scrolled('Canvas',
            -scrollbars => 'os',
            -scrollregion => [0, 0, $initial_width, 125],
            -width => $viewable_width,
            -height => 125,
            -background => randColor()
    )->pack(qw/-fill both -side top -expand 1/);
[download]

Now, when you create a rectangle, be sure to save its ID in the @box array:

    $box[$i] = $sc[$i]->createRectangle($x, 50, $x+20, 90,
            -fill => randColor(),
            -outline => 'black',
            -width => 2,
            -tags => 'rect',
     );
[download]

Here's where things get interesting ...  You have to calculate what x-coordinate in the virtual window (whose width is identified by $initial_width) should be the first point to appear in the visual window (identified by $visual_window).

To calculate this, take the midpoint of the rectangle's coordinates (($x1 + $x2) / 2), and subtract from it one half of the visual window (($x1 + $x2 - $viewable_width) / 2).

Here's the code which implements the alignment:

sub AlignAll{
    my ($x1, $y1, $x2, $y2);
    foreach my $i (0 .. 3) {
        my $sc = $sc[$i];                           # Get Canvas objec
+t
        my $box = $box[$i];                         # Get box id (rect
+angle)
        my ($x1, $y1, $x2, $y2) = $sc->bbox($box);  # Get box coordina
+tes
        my $mid = ($x1 + $x2) / 2;                  # Get midpoint, mi
+nus
        $mid -= $viewable_width / 2;                #   1/2 of visible
+ window
        my $newx = $mid / $initial_width;           # Get delta x-dist
+ance
        $sc->xviewMoveto($newx);                    # Move Canvas obje
+ct
    }
}
[download]

Note that this will work in the absence of zooming.

To make it work for zoom-in and zoom-out, you'll need to make one last set of modifications.  In the anonymous subroutines defined for the first 2 buttons, when you calculate scale, you should then adjust $initial_window by that factor:

$frame->Button(
   -text => " Zoom Out ",
   -width => 10,
   -command => sub {
        $scale*=0.8;
        $initial_width *= $scale;
        foreach  $i (0 .. 3) {
            $sc[$i]->scale(qw/all 0 0 .8 1/);
            $sc[$i]->configure(-scrollregion => [0, 0, $initial_width,
+ 125]);
        }
    }
)->pack(qw/-side left -padx 25/);
$frame->Button(
   -text => " Zoom In ",
   -width => 10,
   -command => sub {
        $scale*=1.25;
        $initial_width *= $scale;
        foreach  $i (0 .. 3) {
            $sc[$i]->scale(qw/all 0 0 1.25 1/);
            $sc[$i]->configure(-scrollregion => [0, 0, $initial_width,
+ 125]);
        }
    }
)->pack(qw/-side left -padx 25/);
[download]

Now it should all work the way you want!

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