Hi. I'm building a data aquisition system in Perl that colects data at the rate of 10 cicles per second, and I'd like to show that in a graph on a Tk window.

If I use Tk::Canvas and create boxes or dots for each aquired data point, soon I'll fill all the memory because, if I understood correctly, each of those points is an entity on Tk.

Using Imager with Tk::photo was tried too, but the convertion from Imager format to PNG, as stated on Tk::Photo example, using base64 takes too long.

GD was also tried, but we need more functionality for the generated graphics.

In fact, what I'm looking for is a suggestion of a way to draw primitives on a canvas that are not items or objects, as was done in the past on VGA screens. The Tk::Photo + Imager solution would be fine if the conversion did not take so long.

Can you suggest me a way of solving this problem?


The following piece of code examples the problem. In a athlon64 notebook it takes 70% of the CPU to run.

#!/usr/bin/perl
use strict;
use Tk;
use Tk::Photo;
use MIME::Base64;
use Tk::PNG;
use Imager;

my $xsize = 200;
my $ysize = 200;

my $cicle;

my ($x, $y) = (int($xsize/2), int($ysize/2));

my $image = Imager->new(xsize=>$xsize, ysize=>$ysize);

my  $blue = Imager::Color->new( 255, 255, 255 );

my $image_data;
$image->write(data =>\$image_data, type=>'png')
  or die "Cannot save image: ", $image->errstr;
$image_data = encode_base64($image_data);

my $main = MainWindow->new;

my $tk_image = $main->Photo(-data => $image_data);
my $screen = $main->Label(-image=>$tk_image)->pack;

my $id = $main->repeat(100,\&move);

MainLoop;

sub move {

  my ($dx, $dy);
  
  my $i = int(rand(100));
  if (($i/5) == int($i/5)) {
    $dx = 0;
  }
  elsif (($i/2) == int($i/2)) {
    $dx = 1;
  }
  else { 
    $dx = -1;
  }

  my $j = int(rand(100));
  if (($j/5) == int($j/5)) {
    $dy = 0;
  }
  elsif (($j/2) == int($j/2)) {
    $dy = 1;
  }
  else { 
    $dy = -1;
  }

  if (($x + $dx) > $xsize) {
    $x = $xsize;
  } 
  elsif (($x + $dx) < 0) {
    $x = 0;
  }
  else {
    $x += $dx;
  }

if (($y + $dy) > $ysize) {
    $y = $ysize;
  } 
  elsif (($y + $dy) < 0) {
    $y = 0;
  }
  else {
    $y += $dy;
  }
  $image->setpixel(x=>$x, y=>$y, color=>$blue);

  $cicle++;
  print "Cicle $cicle. Coords: $x, $y. Diference $dx, $dy.\n";

  $image->write(data =>\$image_data, type=>'png')
    or die "Cannot save image: ", $image->errstr;
  $image_data = encode_base64($image_data);
  
  $tk_image->configure(-data => $image_data);
  $screen->configure(-image=>$tk_image);
}

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In reply to Real time data graphs. by enhering

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