stabu has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

A little project I was doing is taking much longer than I thought, so I thought I would post here and see if anybody could point any way forward.

I want to take an SVG file and produce it at various magnifcations in PNG form. I'm using Image::LibRSVG for this batch file writing procedure, which is probably not what it was built for. 
#!/usr/bin/perl -w
use strict;
use Image::LibRSVG;

my $rsvg = new Image::LibRSVG();
my $infile=$ARGV[0];

for (my $i=1;$i<=10;$i++) {
    my $fs=sprintf("%05d.png",$i); 
    $rsvg->convertAtZoom($infile,$fs,$i/10,$i/10); # be careful 1, is 
+normal zoom, not 100!!!
    undef $fs;
}

undef $rsvg;

[download]
What I would like is to not have the loop reading from file each time .. so I was thinking about referencing it as a filehandle and then dereferencing. A go or no-go area?

Idea is to make the code faster.

A bigger problem is that the output file is a different size each time. So I want to create a set canvas size and map the zoomed output to it. This can be done with GD, but again, Image::LibRSVG insists on saving to file each time. In fact it only has one saveAs method, and that's to write to file. Any ideas for me?

Image::LibRSVG is starting feels more like a wrapper, may be I should be looking into cairo for this.

Thanks for any ideas in advance. Cheers.

Replies are listed 'Best First'.
Re: SVG to many PNG problem
by zentara (Cardinal) on May 01, 2009 at 16:17 UTC
    Use Gtk2's SVG library. Then you can load the svg as a pixbuf, and manipulate, slice and dice, and convert to png. Here is a start. This autoresizes the svg when you resize the window. 
    #!/usr/bin/perl
use warnings;
use strict;
use Glib qw(TRUE FALSE);
use Gnome2::Rsvg;

Gtk2->init;

my $img;

my $mw = Gtk2::Window->new;

$mw->signal_connect (delete_event => sub { Gtk2->main_quit });

my $vbox = Gtk2::VBox->new (FALSE, 4);
$vbox->set_border_width (4);
$vbox->show;

# Create the main box
my $vp = Gtk2::Viewport->new(undef, undef);

# Layout the stuff
$vbox->pack_start ($vp, TRUE, TRUE, 0);
$vp->show;

$mw->add( $vbox ); 

get_svg(400,400);

$mw->signal_connect (event_after => \&event_after);

#$mw->add_events ([qw/ button-press-mask
#                      button-release-mask
#                      key-release-mask
#                /]);

#$mw->signal_connect('button-release-event' => sub {
#        my ($widget,$event) = @_;
#        #count is in the same namespace as the closure
#            print "release\n";
#     });

#$mw->signal_connect (event => sub {
#         my ($item, $event) = @_;
#         warn "event ".$event->type."\n";
#return FALSE;
#});

#$mw->signal_connect (realize => sub {
             #$window->move ($pos->{x}, $pos->{y});
             #$window->resize ($pos->{width}, $pos->{height});
#             print "1\n";
#});

$mw->show;
Gtk2->main;
################################################3
sub get_svg {
    
        my ($x,$y) = @_; 

        $vp->remove($img) if defined $img;
        
    my $file = 'svg.svg';
    
    my $pb = Gnome2::Rsvg->pixbuf_from_file_at_zoom_with_max($file,15,
+15,$x,$y);
        #  ($file, x_zoom, y_zoom, max_x, max_y )

        $img = Gtk2::Image->new_from_pixbuf($pb);

        #($x, $y) = ($pb->get_width, $pb->get_height);
        
    $vp->add($img);
        $img->show;
        
    #will auto expand ????
    #$vp->set_size_request($x,$y);
    
    $vp->set_size_request(.9*$x,.9*$y);
    
    $vp->show; 
    
}
############################################
sub event_after {
  my ($mw, $event) = @_;

  return FALSE unless $event->type eq 'configure'; 
#  print $event->type,"\n"; 
  #return FALSE unless $event->button == 1;
  my ($x, $y) = $mw->get_size;
   print  "$x $y\n";

   get_svg($x,$y);

  return FALSE;
}

    [download]
    I'm not really a human, but I play one on earth.
    Old Perl Programmer Haiku
[reply]
[d/l]
      Many thanks Zentara, that's appreciated.

      I will hack away at that. Cheers!
[reply]
Re: SVG to many PNG problem
by JavaFan (Canon) on May 01, 2009 at 13:11 UTC
    A bigger problem is that the output file is a different size each time.
    Considering that you are taking a fixed vector graphic, and translating it to a compressed bitmapped format changing only the scale, getting different sized outputs is to be expected, isn't?
[reply]
      that's an interesting comment. Yes, it shouldn't be a problem. It is quite definitely a feature of SVG, an essential key to its flexibility. So even more than expecting it, I should have been looking forward to it.

      I'm just looking for the right programming manner in which to express that flexibility. Many features become problems due to a context or situation with unaligned constraints. Choosing Image::LibRSVG and its comparatively small number of methods is just such a situation. And I mean my choice of the module, not the module itself ... I'm taking about the design decision.

      I'm not sure I should apologise though. It's just far too common a perspective to take. At best I was cavalier in calling it a problem. At worst, careless. I could have made two spelling mistakes instead, I don't think it would be graver.
[reply]
        It is quite definitely a feature of SVG, an essential key to its flexibility.
        You've lost me here. Considering that you are writing PNG files, what does that have to do with SVG features?
[reply]

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