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Image-SVG-Path-0.22
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 "SVG standards" for details. Although SVG is a type of XML, the text in the d attribute of SVG paths is not XML but a 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]
    Element 7:
       svg_key -> z
       position -> relative
       type -> closepath

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).

SVG path elements

This section documents the output elements. For example, if we extract the path information from a path $d using

    my @path = extract_path_info ($d);

then each element of @path is a hash reference containing one of the following types of elements and the corresponding hash keys.

An SVG path consists of a sequence of movements from one point to another, so each of the following steps in the path begins from the end point of the previous movement.

Move to elements

svg_key

This is M or m.

point

This is the point to move to.

Line elements

svg_key

This is L or l.

point

This is the end point of the line.

end

This field occurs in some lines for backwards compatibility with pre-0.16 versions of the module.

Cubic bezier curve elements

svg_key

This is C or c.

control1

Control point 1 of the curve.

control2

Control point 2 of the curve.

end

The end point of the curve.

Shortcut cubic bezier curve elements

Use the "no_shortcuts" option to automatically convert these into cubic bezier curve elements.

svg_key

This is S or s.

control2

This is the second control point of the curve (the first one is implicit).

end

This is the end point of the curve.

Quadratic bezier curve elements

svg_key

This is Q or q.

control

This is the control point.

end

This is the end point.

Shortcut quadratic Bezier curves

Use the "no_shortcuts" option to automatically convert these into quadratic bezier curves.

svg_key

This is T or t.

end

This is the end point.

Arc elements

Arcs are omitted from "SVG Tiny".

rx, ry

X and Y radiuses

x_axis_rotation

See the SVG documentation for details.

large_arc_flag

See the SVG documentation for details.

sweep_flag

See the SVG documentation for details.

x, y

These are the end points of the arc.

Horizontal line elements

svg_key

This is H or h.

x

This is the x coordinate of the end point. The y coordinate is implicit.

Vertical line elements

svg_key

This is V or v.

y

This is the y coordinate of the end point. The x coordinate is implicit.

BUGS

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.

SEE ALSO

SVG::Rasterize

This contains a complete parser for SVG paths in SVG::Rasterize::Engine::PangoCairo. It is embedded into the module and is used to draw with Cairo.

MarpaX::Languages::SVG::Parser

This parser uses the SVG grammar mentioned in "BUGS".

SVG standards

The full specification contains all the details. The SVG path specification contains the specifications for paths.

SVG Tiny

SVG Tiny is a subset of SVG. It claims to have a Perl Language Binding, but I cannot locate the source code.

There is also another standard, SVG basic, I'm not too sure whether either this or SVG Tiny are in use.

ACKNOWLEDGEMENTS

Colin Kuskie (http://www.perldreamer.com/) fixed error messages for version 0.20, number paths for version 0.21, and implicit line-tos for version 0.22.

AUTHOR

Ben Bullock, <bkb@cpan.org>

Request

If you'd like to see this module continued, let me know that you're using it. For example, send an email, write a bug report, star the project's github repository, add a patch, add a ++ on Metacpan.org, or write a rating at CPAN ratings. It really does make a difference. Thanks.

COPYRIGHT & LICENCE

This package and associated files are copyright (C) 2011-2016 Ben Bullock.

You can use, copy, modify and redistribute this package and associated files under the Perl Artistic Licence or the GNU General Public Licence.