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

my $mw=MainWindow->new(-title=>"Print out the canvas");
my $c=$mw->Scrolled("Canvas")->pack(-expand=>1,-fill=>'both');
my $canvas=$c->Subwidget("canvas");
$canvas->createLine(100,100,20,20,-arrow=>'both',-arrowshape=>[10,10,1
+0]);
$canvas->createOval(100,80,65,75,-fill=>"blue");
$canvas->createRectangle(30,50,60,80, -fill=>"red",-width=>5);
$canvas->createText(150,1100,-text=>"check postscript",-justify=>"left
+");
$canvas->createOval(150,1150,300,1300,-fill=>"blue");
$canvas->createRectangle(150,1300,400,1350, -fill=>"red",-width=>5);
$canvas->configure(-scrollregion=>[$canvas->bbox("all")]);
$canvas->update();

my $button=$canvas->Button(-text=>"Print",-command=>\&buttonDo)
                            ->pack(-side=>"bottom");
MainLoop;
sub buttonDo{

         $canvas->update;
         my @capture=();
         my ($x0,$y0,$x1,$y1)=$canvas->bbox('all');

         my $width = $x1-$x0;
         my $height = ($y1-$y0)/2;
         print "$width $height\n";
         
         
         @capture=('-x'=>$x0,'-y'=>$y0,-height=>$height,-width=>$width
+);
         
         $canvas -> postscript(-colormode=>'color',
                               -file=>"$0a.ps",
                   -rotate=>0,
            #       -width=> 500,
            #       -height=>500,    
                   @capture);


         @capture=('-x'=>$x0,'-y'=>$height ,-height=>$height,-width=>$
+width);
         
         print $y0 + ($y1-$y0/2),"\n";
         
         
         $canvas -> postscript(-colormode=>'color',
                               -file=>"$0b.ps",
                   -rotate=>0,
                  # -width=> 500,
                  # -height=>500,    
                   @capture);

         
         print "saved\n";
         
    }
[download]

#!/usr/bin/perl
use warnings;
use strict;
use PDF::API2;

my $pdf=PDF::API2->new; # Create a new top-level PDF document
my $font = $pdf->corefont('Helvetica');

my $page1 = $pdf->page();        # Create 1st page
$page1->mediabox(500, 700);  # Set the page dimensions
my $text1 = $page1->text();
$text1->translate(50, 650);  # Position the text
$text1->font($font,12);
$text1->text("Page 1");

my $page2 = $pdf->page();         # Create 2nd page
$page2->mediabox(500, 700);  # Set the page dimensions
my $text2 = $page2->text();
$text2->translate(50, 650);  # Position the text
$text2->font($font,12);
$text2->text("Page 2");

$pdf->saveas("$0.pdf");
$pdf->end;
exit;
[download]

If all else fails, there's also the pstops utility to postprocess the EPS file.  For example

$ pstops '1:0@1(0,0),0@1(0,1h),0@1(0,2h)' in.ps out.ps
[download]

would turn a single-page, 3*A4 long document into 3 separate A4 pages. (0,0) / (0,1h) / (0,2h) in the above command specify the position of the new pages relative to the orginal page (h = unit is page-height, by default typically A4).  See the manpage for the syntax details.

I've never actually done this, so please take the reply with a grain of salt. It does however seem to me, from reading the Tk documentation, that this should be possible.

http://www.tcl.tk/man/tcl8.4/TkCmd/canvas.htm#M60

-x position
Specifies the x-coordinate of the left edge of the area of the canvas that is to be printed, in canvas coordinates, not window coordinates. Defaults to the coordinate of the left edge of the window.

-y position
Specifies the y-coordinate of the top edge of the area of the canvas that is to be printed, in canvas coordinates, not window coordinates. Defaults to the coordinate of the top edge of the window.

-width size
Specifies the width of the area of the canvas to print. Defaults to the width of the canvas window.

-height size Specifies the height of the area of the canvas to print. Defaults to the height of the canvas window.

I may be wrong, but it should then be possible to divide the canvas height by some factor, resulting in a number of pages, and then adjusting the -x -y -width -height parameters and doing one ->postscript() call for each page.

YMMV. Good luck :-)

The program is a little more complicated than shown in my question. When I stated the canvas is long, it can be really long, so in actuality I have coded 2 canvases working together. One acts as a "header" and sits on top of the "data" canvas, allowing the "data" canvas to be scrolled vertically alone, or both canvases to be scrolled horizontally together (think spreadsheets).

I have already looped to break the "data" canvas into paper-sized chunks (resulting in multiple postscript files), but am still working on splicing the "header" part onto each "data" part and then combining all files into 1 file.

I think the pstops will help the most, not in itself, but as an example. I am only able use the standard perl installation (no PDF::API2) and it must be runnable on *nix and Windows.

I guess I really need to learn how to hack postscript.

I'll be the first to say that learning PostScript is no small task; I'm pretty sure you can get around this in cheaper ways.

One way that needs no external tools; What about re-creating the widget(s) making up the header canvas on the data canvas? Place them on the right coordinates for page one, call postscript(), move them to coords for page two, etc.. and just destroy them once you're done printing.

Another possibility is using ImageMagick; you can overlay images using the command-line 'composite' program (may be avaliable through a Perl binding also). This assumes, of course, that you supply a header.ps by either generating it from the header canvas or optionally supplied as a static file from Acrobat or some other tool.
composite header.ps data.ps page.ps
There is also most likely a way to do this using some tool/script in the 'psutils' package http://www.tardis.ed.ac.uk/~ajcd/psutils/. You can use this package to combine several .ps to one file.

Just my two cents. If you post your "dual canvas" code, it's easier to make helpful suggestions :-)