In your code, you don't enlarge the $c_size to account for the *2 scaling, so the fractal moves right off the canvas. If you scale the $canvas with $c_size *=2; in the sub, you quickly drive the cpu into unusability.

You might want to keep the original fractal, and just adjust the scollregion to make it move to appear to center it where you mouse click. In that case it may be better to write the fractal to an image first.

Hmm, unless I've misunderstood something, I'm not sure I agree - my main cpu worry is the amount of lines I'm throwing at the canvas. As far as the main computing goes, since I don't increase (yet:) the number of iterations at different scales, the number of calculations is fixed.

Also, my code worked fine when I didn't try to center the fractal on the location clicked on - i.e. it just zoomed in.

In theory, all I've got to do is adjust the start points for the calculation to see a different area, and it *almost* works with the current code, but something's going screwy. I think what I need to do is to remove the mandlebrot from the equation (sic), and just get some debugging output... sigh...

map{$a=1-$_/10;map{$d=$a;$e=$b=$_/20-2;map{($d,$e)=(2*$d*$e+$a,$e**2
-$d**2+$b);$c=$d**2+$e**2>4?$d=8:_}1..50;print$c}0..59;print$/}0..20
[download]

Tom Melly, pm@tomandlu.co.uk

Well I played with your code, and what I think you need to do is reset the canvas size and scrollregion when you call the sub. The way your current code works, you make the fractal bigger, but never adjust the canvas size to accomodate it. This is as far as I got, before the cpu usage made me give it up. I added scrollregions, adjust $c_size with $scale, and set the $scale to 1.2 to troubleshoot easier. Anyways, click this a few times and watch what happens, compared to your original script.

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

my $c_size = 100;
my $scale = 1;

my $mw = MainWindow -> new;
my $canvas = $mw -> Scrolled('Canvas',
         -height=>$c_size, 
     -width=>$c_size,
     -scrollregion => [0,0,$c_size,$c_size]
     )-> pack(-expand=>1 ,-fill=>'both');
     
$canvas -> Tk::bind('all', '<ButtonPress-1>' => \&MakeMan);
&MakeMan();

MainLoop;

sub MakeMan(){
  my ($e, $canv_x, $canv_y)=(0,$c_size/2,$c_size/2);
  if($scale > 1){
    $e = $canvas -> XEvent;
    $canv_x = $e->x;
    $canv_y = $e->y;
  }

  my $icount = 1;
  
  $c_size *= $scale;
  
#problem here...
  my $i = -2/$scale + (($canv_y-($c_size/2)) / ($c_size/$scale));# + $
+lasti;
  my $rgb;
  while($icount <= $c_size){
#... and here...
    my $r = -2/$scale + (($canv_x-($c_size/2)) / ($c_size/$scale));# +
+ $lastr;
    my $rcount = 1;
    while($rcount <= $c_size){
      my $tr = $r;
      my $ti = $i;
      $rgb = '#000000';
      for my $n(1..15){
        ($tr, $ti) = (($tr ** 2) - ($ti ** 2) + ($r), (2 * $tr * $ti) 
++ ($i));
        if((($tr * $tr) + ($ti * $ti)) > 4){
          $rgb = '#ffffff';
          last;
        }
      }
      $canvas -> createLine($rcount, $icount, $rcount+1, $icount, -fil
+l => $rgb, -width => 1);
      $rcount ++;
      $r += (4/$scale)/$c_size;
    }
    $icount ++;
    $i += (4/$scale)/$c_size;
  }
  $scale = $scale * 1.2;

$canvas->configure(-scrollregion=>[0,0,$c_size,$c_size]);
$canvas->update;

}
[download]

---

I'm not really a human, but I play one on earth. Cogito ergo sum a bum

For instance, tag all your lines with 'fractal', after you build the fractal, get a bbox of the tag fractal, take the midpoint values, and store it. Then on each new fractal build, just repeat, take the new bbox, then compute how much you need to move it, to center it on the mouse event point.

I'm not doing the computations here, but this shows the basics.

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

my $c_size = 100;
my $scale = 1;

my $centerx;
my $centery;


my $mw = MainWindow -> new;
my $canvas = $mw -> Canvas(-height=>$c_size, -width=>$c_size) -> pack;

$canvas -> Tk::bind('all', '<ButtonPress-1>' => [\&transit,Ev('x'), Ev
+('y') ]);

&MakeMan();

MainLoop;

sub transit{
  my ($canv, $x, $y) = @_;
  print "(x,y) = ", $canv->canvasx($x), ", ", $canv->canvasy($y), "\n"
+;
 
 my $dx = $x - $centerx;
 my $dy = $y - $centery;

  $canvas->move('fractal',$dx,$dy);
}

sub MakeMan(){
  my ($e, $canv_x, $canv_y)=(0,$c_size/2,$c_size/2);
  if($scale > 1){
    $e = $canvas -> XEvent;
    $canv_x = $e->x;
    $canv_y = $e->y;
  }

  my $icount = 1;
#problem here...
  my $i = -2/$scale + (($canv_y-($c_size/2)) / ($c_size/$scale));# + $
+lasti;
  my $rgb;
  while($icount <= $c_size){
#... and here...
    my $r = -2/$scale + (($canv_x-($c_size/2)) / ($c_size/$scale));# +
+ $lastr;
    my $rcount = 1;
    while($rcount <= $c_size){
      my $tr = $r;
      my $ti = $i;
      $rgb = '#000000';
      for my $n(1..15){
        ($tr, $ti) = (($tr ** 2) - ($ti ** 2) + ($r), (2 * $tr * $ti) 
++ ($i));
        if((($tr * $tr) + ($ti * $ti)) > 4){
          $rgb = '#ffffff';
          last;
        }
      }
      $canvas -> createLine($rcount, $icount, 
                     $rcount+1, $icount, 
             -fill => $rgb, 
             -width => 1,
             -tags => ['fractal']
             );
      $rcount ++;
      $r += (4/$scale)/$c_size;
    }
    $icount ++;
    $i += (4/$scale)/$c_size;
  }
  $scale = $scale * 2;

my ($x1,$y1,$x2,$y2) = $canvas->bbox('fractal');

$centerx = ($x1+$x2)/2;
$centery = ($y1+$y2)/2;

print "center-> $centerx $centery\n";

}
[download]

Well, I don't know if it's what you intended, but you gave me a clue to solving the problem - I was making my job much harder than it needed to be by constantly trying to handle transitions from Mandelbrot scale to canvas scale + edges to centre...

y concentrating on tracking the center I was able finally to get my head around what was needed... below is the working code - you can pass it a param of canvas size (e.g. "200"), or just let it use the default of 100.

Thanks all.

use strict;
use Tk;

my $c_size = ($ARGV[0] =~ /^\d+$/ && $ARGV[0]>0) ? $ARGV[0] : 100;
my $scale = my $oldscale = 1;
my ($lasti, $lastr)=(0,-0.5);

my $mw = MainWindow -> new;
my $canvas = $mw -> Canvas(-height=>$c_size, -width=>$c_size) -> pack;
$canvas -> Tk::bind('all', '<ButtonPress-1>' => \&MakeMan);
MakeMan();

MainLoop;

sub MakeMan(){
  $canvas -> delete('all');
  my ($e, $canv_x, $canv_y)=(0,$c_size/2,$c_size/2);
  if($scale > 1){
    $e = $canvas -> XEvent;
    $canv_x = $e->x;
    $canv_y = $e->y;
  }

  my $px_old = (4/$oldscale)/$c_size;
  my $px_new = (4/$scale)/$c_size;
  
  my $i = $lasti = $lasti + ($canv_y - ($c_size/2))*$px_old; # centre
  $i = $i - (($c_size/2)*$px_new); # left edge
  my $rconst = $lastr = $lastr + ($canv_x - ($c_size/2))*$px_old; # ce
+ntre
  $rconst = $rconst - (($c_size/2)*$px_new); # top edge

  my $icount = 1;
  while($icount <= $c_size){
    my $r = $rconst;
    my $rcount = 1;
    while($rcount <= $c_size){
      my $iter = ($c_size/10)*($scale**0.5);
      my $tr = $r;
      my $ti = $i;
      my $rgb_out = '#000000';
      my $rgb = 255;
      for my $n(1..$iter){
        ($tr, $ti) = (($tr ** 2) - ($ti ** 2) + ($r), (2 * $tr * $ti) 
++ ($i));
        $rgb -= int(255/$iter);
        if((($tr * $tr) + ($ti * $ti)) > 4){
          $rgb_out = '#' . (sprintf("%2.2X", $rgb))x3;
          last;
        }
      }
      $canvas -> createLine($rcount, $icount, $rcount+1, $icount, -fil
+l => $rgb_out, -width => 1);
      $rcount ++;
      $r += ((4/$scale)/$c_size);
    }
    $icount ++;
    $i += ((4/$scale)/$c_size);
  }
  $oldscale = $scale;
  $scale = $scale * 2;
}
[download]

map{$a=1-$_/10;map{$d=$a;$e=$b=$_/20-2;map{($d,$e)=(2*$d*$e+$a,$e**2
-$d**2+$b);$c=$d**2+$e**2>4?$d=8:_}1..50;print$c}0..59;print$/}0..20
[download]

Tom Melly, pm@tomandlu.co.uk