/ 
Image-SVG-Path-0.07
River stage one • 1 direct dependent • 2 total dependents
/ Image::SVG::Path

NAME

Image::SVG::Path - read the "d" attribute of an SVG path

SYNOPSIS

use Image::SVG::Path 'extract_path_info';
my @path_info = extract_path_info ($path_d_attribute);

DESCRIPTION

This module extracts information contained in the "d" attribute of an SVG <path> element and turns it into a simpler series of steps.

For example, an SVG <path> element might take the form

<path d="M9.6,20.25c0.61,0.37,3.91,0.45,4.52,0.34c2.86-0.5,14.5-2.09,21.37-2.64c0.94-0.07,2.67-0.26,3.45,0.04"/>

Using an XML parser, such as XML::Parser,

use XML::Parser;
use Image::SVG::Path 'extract_path_info';
my $p = XML::Parser->new (Handlers => {Start => \& start});
$p->parsefile ($file)
    or die "Error $file: ";

sub start
{
    my ($expat, $element, %attr) = @_;

    if ($element eq 'path') {
        my $d = $attr{d};
        my @r = extract_path_info ($d);
        # Do something with path info in @r
    }
}

SVG means "scalable vector graphics" and it is a standard of the W3 consortium. See http://www.w3.org/TR/SVG/ for the full specification. See http://www.w3.org/TR/SVG/paths.html for the specification for paths. Although SVG is a type of XML, the text in the d attribute of SVG paths is not in the XML format but in a more condensed form using single letters and numbers. This module is a parser for that condensed format.

FUNCTIONS

extract_path_info

my @path_info = extract_path_info ($path_d_attribute);

Turn the SVG path string into a series of simpler things. For example,

my @path_info = extract_path_info ('M6.93,103.36c3.61-2.46,6.65-6.21,6.65-13.29c0-1.68-1.36-3.03-3.03-3.03s-3.03,1.36-3.03,3.03s1.36,3.03,3.03,3.03C15.17,93.1,10.4,100.18,6.93,103.36z');

my $count = 0;
for my $element (@path_info) {                
    $count++;                                 
    print "Element $count:\n";                
    for my $k (keys %$element) {              
        my $val = $element->{$k};             
        if (ref $val eq 'ARRAY') {            
            $val = "[$val->[0], $val->[1]]";  
        }                                     
        print "   $k -> $val\n";              
    }                                         
}

This prints out

Element 1:                         
   point -> [6.93, 103.36]         
   svg_key -> M                    
   position -> absolute            
   type -> moveto                  
Element 2:                         
   control1 -> [3.61, -2.46]       
   svg_key -> c                    
   control2 -> [6.65, -6.21]       
   position -> relative            
   type -> cubic-bezier            
   end -> [6.65, -13.29]           
Element 3:                         
   control1 -> [0, -1.68]          
   svg_key -> c                    
   control2 -> [-1.36, -3.03]      
   position -> relative            
   type -> cubic-bezier            
   end -> [-3.03, -3.03]           
Element 4:                         
   svg_key -> s                    
   control2 -> [-3.03, 1.36]       
   position -> relative            
   type -> shortcut-cubic-bezier   
   end -> [-3.03, 3.03]            
Element 5:                         
   svg_key -> s                    
   control2 -> [1.36, 3.03]        
   position -> relative            
   type -> shortcut-cubic-bezier   
   end -> [3.03, 3.03]             
Element 6:                         
   control1 -> [15.17, 93.1]       
   svg_key -> C                    
   control2 -> [10.4, 100.18]      
   position -> absolute            
   type -> cubic-bezier            
   end -> [6.93, 103.36]

The return value is a list of hash references. Each hash reference has at least three keys, type, position, and svg_key. The type field says what type of thing it is, for example a cubic bezier curve or a line. The position value is either "relative" or "absolute" depending on whether the coordinates of this step of the path are relative to the current point (relative) or to the drawing's origin (absolute). The svg_key field is the original key from the path. position is relative if this key is lower case and absolute if this key is upper case.

If type is moveto, the hash reference contains one more field, point, which is the point to move to. This is an array reference containing the x and y coordinates as elements indexed 0 and 1 respectively.

If the type is cubic-bezier, the hash reference contains three more fields, control1, control2 and end. The value of each is an array reference containing the x and y coordinates of the first and second control points and the end point of the Bezier curve respectively. (The start point of the curve is the end point of the previous part of the path.)

If the type is shortcut-cubic-bezier, the hash contains two more fields, control2 and end. control2 is the second control point, and end is the end point. The first control point is got by reflecting the second control point of the previous curve around the end point of the previous curve (the start point of the current curve).

There is also an option "no_shortcuts" which automatically replaces shortcut cubic bezier curves with the normal kind, by calculating the first control point.

A second argument to extract_path_info contains options for the extraction in the form of a hash reference. For example,

my @path_info = extract_path_info ($path, {absolute => 1});

The following may be chosen by adding them to the hash reference:

absolute

If the hash element absolute is set to a true value, relative positions are changed to absolute. For example a "c" curve is changed to the equivalent "C" curve.

no_shortcuts

If the hash element no_shortcuts is set to a true value then shortcuts ("S" curves) are changed into the equivalent "C" curves. A deficiency of this is that it only works in combination with the "absolute" option, otherwise it does nothing.

verbose

If this is set to a true value, extract_path_info prints out informative messages about what it is doing as it parses the path.

reverse_path

my $reverse_path = reverse_path ($path);

Make an SVG path which is the exact reverse of the input.

BUGS

This only works for cubic bezier curves with absolute position and no shortcuts (C elements only). It doesn't fill in all the information correctly.

create_path_string

my $path = create_path_string (\@info);

Given a set of information as created by "extract_path_info", turn them into an SVG string representing a path.

BUGS

This only works for cubic bezier curves and the initial moveto element for absolute position and no shortcuts (C elements only).

DIAGNOSTICS

BUGS

Only cubic bezier curves and lines

This module only parses movetos (m elements), cubic bezier curves (s and c elements) and lines (l elements). It does not parse quadratic bezier curves (q and t elements), elliptical arcs (a elements), or horizontal and vertical linetos (h and v elements).

Does not use the grammar

There is a grammar for the paths in the W3 specification. See http://www.w3.org/TR/SVG/paths.html#PathDataBNF. However, this module does not use that grammar. Instead it hacks up the path using regexes.

EXPORTS

The module exports "extract_path_info" on demand, so

use Image::SVG::Path 'extract_path_info';

imports it.

AUTHOR

Ben Bullock, <bkb@cpan.org>

LICENCE

This module and all associated files can be used, modified and distributed under either the Perl artistic licence or the GNU General Public Licence.