NAME

SVG::Rasterize - rasterize SVG content to pixel graphics

VERSION

Version 0.003001

SYNOPSIS

    use SVG;
    use SVG::Rasterize;

    my $svg = SVG->new(width => 300, height => 200);
    $svg->line(x1 => 10, y1 => 20, x2 => 220, y2 => 150,
               style => {stroke => 'black', stroke-width => '2pt' });

    # add more svg content
    # .
    # .
    # .

    my $rasterize = SVG::Rasterize->new();
    $rasterize->rasterize(svg => $svg);
    $rasterize->write(type => 'png', file_name => 'out.png');

DESCRIPTION

SVG::Rasterize can be used to rasterize SVG objects to pixel graphics (currently png only) building on the Cairo library (by default, other underlying rasterization engines could be added). The direct rasterization of SVG files might be implemented in the future, right now you should have a look at SVG::Parser which can generate an SVG object from an svg file.

Motivation

In the past, I have used several programs to rasterize SVG graphics including Inkscape, Konqueror, Adobe Illustrator, and rsvg. While Inkscape was my favourite none of them made me entirely happy. There were always parts of the standard that I would have liked to use, but were unsupported.

So finally, I set out to write my own rasterization engine. The ultimate goal is complete compliance with the requirements for a Conforming Static SVG Viewer as described in the SVG specification: http://www.w3.org/TR/SVG11/conform.html#ConformingSVGViewers. Obviously, this is a long way to go. I do not know if any support for the dynamic features of SVG will ever be added. Anyway, the priority for SVG::Rasterize is accuracy, not speed.

Status

The following elements are drawn at the moment:

path
all basic shapes: rect, circle, ellipse, line, polyline, polygon.

The inheritance of styling properties is implemented. The following attributes are at least partly interpreted:

transform
viewBox
preserveAspectRatio
style
fill and all associated properties
stroke and all associated properties

I hope that the interface described here will be largely stable. However, this is not guaranteed. Some features are documented as likely to change, but everything is subject to change at this early stage.

Here is my current view of the next part of the roadmap:

Version 0.004

text basics

Version 0.005

gradients and patterns
clipping paths
masks

INTERFACE

Constructors

new

  $rasterize = SVG::Rasterize->new(%args)

Creates a new SVG::Rasterize object and calls init(%args). If you subclass SVG::Rasterize overload init, not new.

init goes through the arguments given to new. If a method of the same name exists it is called with the respective value as argument. This can be used for attribute initialization. Some of the values can be also given to rasterize to temporarily override the attribute values. The values of these overridable attributes are only validated once they are used by rasterize.

The most commonly used arguments are:

svg (optional): A DOM object to render.
width (optional): width (in pixels) of the generated output image
height (optional): height (in pixels) of the generated output image.

Public Attributes

svg

Holds the DOM object to render. It does not have to be a SVG object, but it has to offer a getNodeName, a getAttributes, and a getChildren method analogous to those defined by the SVG class. If a different object is given to rasterize then the latter one overrules this value temporarily (i.e. without overwriting it).

width

The width of the generated output in pixels.

height

The height of the generated output in pixels.

state

Readonly attribute. Holds the current SVG::Rasterize::State object during tree traversal.

There are other attributes that influence unit conversions, white space handling, and the choice of the underlying rasterization engine. See ADVANCED TOPICS.

Methods for Users

rasterize

  $rasterize->rasterize(%args)

Traverses through the given SVG content and renders the output. Does not return anything.

Examples:

  $rasterize->rasterize(svg => $svg);
  $rasterize->rasterize(svg => $svg, width => 640, height => 480);
  $rasterize->rasterize(svg => $svg, engine_class => 'My::Class');

Supported parameters:

svg (optional): DOM object to rasterize. If not specified the value of the svg attribute is used. One of them has to be set and has to provide the getNodeName, getAttributes, and getChildren DOM methods.

The element can be any valid SVG element, e.g. <svg>, <g>, or even just a basic shape element or so.
width (optional): width of the target image in pixels, temporarily overrides the width attribute.
height (optional): height of the target image in pixels, temporarily overrides the height attribute.
engine_class (optional): alternative engine class to SVG::Rasterize::Cairo, temporarily overrides the engine_class attribute. See SVG::Rasterize::Cairo for details on the interface. The value has to match the regular p_PACKAGE_NAME.
engine_args (optional): arguments for the constructor of the rasterization engine, temporarily overriding the engine_args attribute (NB: in the future, this behaviour might be changed such that the two hashes are merged and only the values given here override the values in the attribute engine_args; however, at the moment, the whole hash is temporarily replaced if the parameter exists). The width and height of the output image can be set in several ways. The following values for the width are used with decreasing precedence (the same hierarchy applies to the height):

1. engine_args->{width}, given to rasterize

2. $rasterize->engine_args->{width}

3. width, given to rasterize

4. $rasterize->width

5. the width attribute of the root SVG object.
normalize_attributes (optional): Influences White Space Handling, temporarily overrides the normalize_attributes attribute. Defaults to 1.

If width (the same applies to height) is 0 it is treated as not set. If you encounter any scenario where you would wish an explicit size of 0 to be treated in some other way let me know.

If width and/or height are not specified they have to have absolute values in the root SVG element. If both the root SVG element and the rasterize method have width and/or height settings then the rasterize parameters determine the size of the output image and the specified SVG viewport is mapped to this image taking the viewBox and preserveAspectRatio attributes into account if they are present. See http://www.w3.org/TR/SVG11/coords.html#ViewportSpace for details.

The user can influence the rasterization process via hooks. See the Hooks section below.

write

  $rasterize->write(%args)

Writes the rendered image to a file.

Example:

  $rasterize->write(type => 'png', file_name => 'foo.png');

The supported parameters depend on the rasterization backend. The write method hands all parameters over to the backend. See write in SVG::Rasterize::Cairo for an example.

Methods for Developers

init

  $rasterize->init(%args)

If you overload init, your method should also call this one.

For each given argument, init calls the accessor with the same name to initialize the attribute. If such an accessor (or in fact, any method of that name) does not exist a warning is printed and the argument is ignored. Readonly attributes that are allowed to be set at initialization time are set separately at the beginning.

in_error

Expects an exception object or error message. Creates a fresh SVG::Rasterize::State object (without any transfrom etc.) and calls in_error_hook (which by default draws a translucent checkerboard across the image). After that, it dies with the given message.

Before you call in_error directly, check out SVG::Rasterize::Exception.

Class Methods

multiply_matrices

2D affine transformation can be represented by 3 x 3 matrices of the form:

  ( a  c  e )
  ( b  d  f )
  ( 0  0  1 )

In this case, the concatenation of such transformations is represented by canonical matrix multiplication. This method takes two ARRAY references of the form [a, b, c, d, e, f] whose entries correspond to the matrix entries above and returns an ARRAY reference with 6 entries representing the product matrix.

The method can be called either as subroutine or as class method or as object method:

  $product = multiply_matrices($m, $n)
  $product = SVG::Rasterize->multiply_matrices($m, $n)
  $product = $rasterize->multiply_matrices($m, $n)

Note that multiply_matrices does not perform any input check. It expects that you provide (at least) two ARRAY references with (at least) 6 numbers each. If you pass more parameters then the last two are used. If they contain more than 6 entries then the first 6 are used.

endpoint_to_center

  @result = endpoint_to_center(@input)
  @result = SVG::Rasterize->endpoint_to_center(@input)
  @result = $rasterize->endpoint_to_center(@input)

Rasterization engines like SVG::Rasterize::Cairo might use center parameterization instead of endpoint parametrization of an elliptical arc (see http://www.w3.org/TR/SVG11/implnote.html#ArcImplementationNotes). This method calculates the center parameters from the endpoint parameters given in a SVG path data string. As indicated above, it can be called as a subroutine or a class method or an object method. The required parameters are:

x coordinate of the starting point
y coordinate of the starting point
radius in x direction
radius in y direction
angle by which the ellipse is rotated with respect to the positive x axis (in radiant, not degrees)
large arc flag
sweep flag
x coordinate of the end point
y coordinate of the end point.

If the reparameterization cannot be computed an empty list is returned. This can have to possible reasons. Either one of the radii is equal (with respect to machine precision) to 0 or the start and end point of the arc are equal (with respect to machine precision). The first case should have been checked before (note that no rounding problems can occur here because no arithmetics is done with the passed values) because in this case the arc should be turned into a line. In the second case, the arc should just not be drawn. Be aware that this latter case includes a full ellipse. This means that a full ellipse cannot be drawn as one arc. The SVG specification is very clear on that point. However, an ellipse can be drawn as two arcs.

Note that the input values are not validated (e.g. if the values are numbers, if the flags are either 0 or 1 and so on). It is assumed that this has been checked before. Furthermore, it is not checked if the radii are very close to 0 or start and end point are nearly equal.

A list of the following parameters is returned (unless an empty list is returned due to the reasons mentioned above):

x coordinate of the center
y coordinate of the center
radius in x direction

This value might have been increased to make the ellipse big enough to connect start and end point. If it was negative the absolute value has been used (so the return value is always positive).
radius in y direction

This value might have been increased to make the ellipse big enough to connect start and end point. If it was negative the absolute value has been used (so the return value is always positive).
start angle in radiant
sweep angle (positive or negative) in radiant.

adjust_arc_radii

  @result = adjust_arc_radii(@input)
  @result = SVG::Rasterize->adjust_arc_radii(@input)
  @result = $rasterize->adjust_arc_radii(@input)

The SVG specification requires that the radii of an elliptic arc are increased automatically if the given values are too small to connect the given endpoints (see http://www.w3.org/TR/SVG11/implnote.html#ArcImplementationNotes). This situation can arise from rounding errors, but also for example during an animation. Moreover, if a given radius is negative then the absolute value is to be used. This method takes care of these adjustments and returns the new values plus some intermediate values that might be useful for callers, namely endpoint_to_center.

In detail, it requires the following parameters:

x coordinate of the starting point
y coordinate of the starting point
radius in x direction
radius in y direction
angle phi by which the ellipse is rotated with respect to the positive x axis (in radiant)
x coordinate of the end point
y coordinate of the end point.

Note that the input values are not validated (e.g. if the values are numbers etc.). It is assumed that this has been checked before. Furthermore, it is not checked if the radii are very close to 0 or start and end point are nearly equal.

The following values are guaranteed to be returned:

adjusted absolute value of the radius in x direction
adjusted absolute value of the radius in y direction

This is all if one of the radii is equal to 0. Otherwise, the following additional values are returned:

sin(phi)
cos(phi)
x_1' (see SVG specification link above)
y_1' (see SVG specification link above)
1 / Lambda - 1

This value is only returned if Lambda is greater than 0 which is equivalent (assuming exact arithmetics) to the end point of the arc being different to the starting point. Lambda is the value calculated in equation (F.6.6.2) of the specification (see link above). 1 / Lambda - 1 is equal to the radicand in equation (F.6.5.2).

ADVANCED TOPICS

Units

SVG supports the absolute units px, pt, pc, cm, mm, in, and the relative units em, ex, and %. Lengths can also be given as numbers without unit which is then interpreted as px. See http://www.w3.org/TR/SVG11/coords.html#Units.

SVG::Rasterize stores default values for unit conversion rates as class variables. You can either change these values or the corresponding object variables. If you have only one SVG::Rasterize object both approaches have the same effect.

The default values are listed below. Except px_per_in, they are taken from the CSS specification. See http://www.w3.org/TR/2008/REC-CSS2-20080411/syndata.html#length-units. The default for px_per_in is arbitrarily set to 90.

Currently, the relative units listed above are not supported by SVG::Rasterize.

Unit conversions:

px_per_in

Pixels per inch. Defaults to 90.
dpi

Alias for px_per_in. This is realized via a typeglob copy:
```
  *dpi = \&px_per_in
```
in_per_cm

Inches per centimeter. Defaults to 1/2.54. This is the internationally defined value. I do not see why I should prohibit a change, but it would hardly make sense.
in_per_mm

Inches per millimeter. Defaults to 1/25.4. This is the internationally defined value. I do not see why I should prohibit a change, but it would hardly make sense.
in_per_pt

Inches per point. Defaults to 1/72. According to [1], this default was introduced by the Postscript language. There are other definitions. However, the CSS specification is quite firm about it.
in_per_pc

Inches per pica. Defaults to 1/6. According to the CSS specification, 12pc equal 1pt.
map_abs_length
```
  $number = $rasterize->map_abs_length($length)
  $number = $rasterize->map_abs_length($number, $unit)
```
This method takes a length and returns the corresponding value in px according to the conversion rates above. Surrounding white space is not allowed.

Examples:
```
  $x = $rasterize->map_abs_length('5.08cm');  # returns 180
  $x = $rasterize->map_abs_length(10);        # returns 10
  $x = $rasterize->map_abs_length(10, 'pt')   # returns 12.5
  $x = $rasterize->map_abs_length('  1in ');  # error
  $x = $rasterize->map_abs_length('50%')      # error
```
The unit has to be absolute, em, ex, and % trigger an exception. See map_length in SVG::Rasterize::State.

There are two different interfaces. You can either pass one string or the number and unit separately. NB: In the second case, the input is not validated. This interface is meant for situations where the length string has already been parsed (namely in map_length in SVG::Rasterize::State) to avoid duplicate validation. The number is expected to match A_NUMBER and the unit to match UNIT (see below). However, it is still checked if the unit is absolute.

The corresponding class attributes are listed below. Note that these values are not validated. Take care that you only set them to numbers.

PX_PER_IN

Defaults to 90.
DPI

Alias for PX_PER_IN. This is realized via a typeglob copy
```
  *DPI = \$PX_PER_IN
```
IN_PER_CM

Defaults to 1/2.54.
IN_PER_MM

Defaults to 1/25.4.
IN_PER_PT

Defaults to 1/72.
IN_PER_PC

Defaults to 1/6.

Lengths versus Numbers

The SVG specification determines which values (e.g. in attributes) are lengths (numbers possibly with a unit) and which are numbers (without a unit). Some attributes have to be numbers although a length would make sense (e.g. in the viewBox attribute or a translate in a transform attribute). SVG::Rasterize aims for strict compliance with the specification. However, in the future there might be a relax attribute which when turned to 1 or higher allows a more and more relaxed interpretation.

White Space Handling

The XML specification (http://www.w3.org/TR/2006/REC-xml11-20060816/#AVNormalize) states that an attribute value unless it is of the type CDATA shall be normalized such that leading and trailing white space is removed and internal white space is flattened to single space characters. XML entities can complicate this normalization, see the specification for details.

If the SVG tree to be rasterized by SVG::Rasterize comes out of an parsed XML document then the parser should have performed this normalization already. However, the tree might also be constructed directly using the SVG module. In order to prevent SVG::Rasterization from choking on an attribute like stroke-width="2pt " it performs by default an additional normalization run:

  $value =~ s/^$WSP*//;
  $value =~ s/$WSP*$//;
  $value =~ s/$WSP+/ /g;

where

  $WSP = qr/[\x{20}\x{9}\x{D}\x{A}]/;  # space, tab, CR, LF

To prevent this normalization, you can set the normalize_attributes attribute (as object attribute or as parameter to rasterize to a false value.

Hooks

The rasterize method traverses through the SVG tree and creates an SVG::Rasterize::State object for each node (at least each node of relevance). Hooks allow you to execute your own subroutines at given steps of this traversal. However, the whole hook business is experimental at the moment and likely to change. Right now, to set your own hooks you can set one of the following attributes to a code reference of your choice.

Currently, there are for hooks:

before_node_hook

Executed at encounter of a new node right before the new SVG::Rasterize::State object is created. It is called as an object method and receives the SVG::Rasterize object, the node object (during DOM tree traversal, otherwise undef), the node name, and the the node attributes (as HASH reference). The attribute values have already been normalized at this stage (see White Space Handling above).
start_node_hook

Executed right after creation of the SVG::Rasterize::State object. The attributes have been parsed, properties and matrix have been set etc. The method receives the SVG::Rasterize object and the SVG::Rasterize::State object as parameters.
end_node_hook

Executed right before the SVG::Rasterize::State runs out of scope because the current node is done with. The method receives the SVG::Rasterize object and the SVG::Rasterize::State object as parameters.
in_error_hook

Executed right before die when the document is in error (see In error below. Receives the SVG::Rasterize object and a newly created SVG::Rasterize::State object as parameters.

Examples:

  $rasterize->start_node_hook(sub { ... })

Rasterization Backend

SVG::Rasterize does not render pixel graphics itself. By default, it uses the cairo library through its Perl bindings. The interface is documented in SVG::Rasterize::Cairo. However, this interface could also be implemented by other backends. In the future, it will be documented in SVG::Rasterize::Cairo. Currently, it has to be considered unstable, though, and the documentation is sparse.

engine_class

This attribute defaults to SVG::Rasterize::Cairo. It can be set as an object attribute or temporarily as a parameter to the rasterize method.

engine_args

This attribute can hold a HASH reference. The corresponding hash is given to the constructor of the rasterization engine when it is called by rasterize. engine_args can be set as an object attribute or temporarily as a parameter to the rasterize method.

engine

  $rasterize->engine

This attribute holds the interface object to the rasterization backend, by default a SVG::Rasterize::Cairo object. The object is created by the rasterize method.

The attribute is readonly, but, of course, you are able to manipulate the object directly via its methods. However, this is not part of the normal workflow and you do this on your own risk ;-).

`SVG` Validation

SVG::Rasterize is not an SVG validator. It does check a lot of things including the validity of the element hierarchy, the required presence and absence of attributes and the values of all attributes in interpretes plus some that it does not interprete. However, it does not (and probably will never) claim to detect all errors in an SVG document.

EXAMPLES

There are a few example scripts in the examples directory of the tar ball. However, they rather illustrate the currently supported SVG subset than options of SVG::Rasterize.

DIAGNOSTICS

Error processing

The SVG documentation specifies how SVG interpreters should react to certain incidents. The relevant section can be found here: http://www.w3.org/TR/SVG11/implnote.html#ErrorProcessing.

This section describes how some of these instructions are implemented by SVG::Rasterize and how it reacts in some other situations in which the specification does not give instructions.

In error

According to the SVG specification (see http://www.w3.org/TR/SVG11/implnote.html#ErrorProcessing, a document is "in error" if:

"the content does not conform to the XML 1.0 specification, such as the use of incorrect XML syntax"

SVG::Rasterize currently does not parse SVG files and will therefore not detect such an error.
"an element or attribute is encountered in the document which is not part of the SVG DTD and which is not properly identified as being part of another namespace"

Currently, SVG::Rasterize will also reject elements that are properly identified as being part of another namespace.
"an element has an attribute or property value which is not permissible according to this specification"

This is checked for those attributes and properties that are currently supported by SVG::Rasterize. Values that are currently ignored may or may not be checked.
"Other situations that are described as being in error in this specification"

In these cases, the rendering is supposed to stop before the incriminated element. Exceptions are path, polyline, and polygon elements which are supposed to be partially rendered up to the point where the error occurs.

Furthermore, a "highly perceivable indication of error shall occur. For visual rendering situations, an example of an indication of error would be to render a translucent colored pattern such as a checkerboard on top of the area where the SVG content is rendered."

In SVG::Rasterize this is done by the in_error_hook. By default, it indeed draws a translucent (rgb(45, 45, 45) with opacity 0.6) checkerboard with 8 fields along the width or height (whichever is shorter). This behaviour can be changed by setting the in_error_hook. Setting the hook to undef or sub {} will disable the process.

`SVG::Rasterize` exceptions

When SVG::Rasterize encounters a problem it usually throws an exception. The cases where only a warning is issued a rare. This behaviour has several reasons:

If the document is in error (see section above) the SVG specification requires that the rendering stops.
In case of failed parameter validation, Params::Validate expects the code execution to stop. One could work around this in an onerous and fragile way, but I will not do this.
Often there is no good fallback without knowing what the user inteded to do. In these cases, it is better to just bail out and let the user fix the problem himself.
A too forgiving user agent deludes the user into bad behaviour. I think that if the rules are clear, a program should enforce them rather strictly.

The exceptions are thrown in form of objects. See Exception::Class for a detailed description. See below for a description of the classes used in this distribution. All error messages are described in SVG::Rasterize::Exception.

Invalid and numerically unstable values

There are situations where certain values cannot be dealt with, e.g. denominators of 0 or negative radicands. Examples are skews of 90 degrees or elliptical arcs where one radius is 0. In these situations, SVG::Rasterize checks for these cases and acts accordingly. Great care is taken to check directly those values which are used as denominator, radicand etc. and not some mathematically equivalent expression which might evaluate to a slightly different value due to rounding errors. However, it is not checked if such an expression is very close to a critical value which might render the processing numerically unstable. I do not want to impose a certain notion of "too close" on SVG authors. Instead it is left to them to check for these border cases. However, the underlying rasterization engine might still impose boundaries.

Exceptions

SVG::Rasterize currently uses the following exception classes. This framework is experimental and might change considerably in future versions. See Exception::Class on how you can make use of this framework. See SVG::Rasterize::Exception for a detailed list of error messages.

SVG::Rasterize::Exception::Base

Base class for the others. Defines the state attribute which holds the current SVG::Rasterize::State object at the time the exception is thrown.
SVG::Rasterize::Exception::InError

The processing encountered an error in the SVG content.
SVG::Rasterize::Exception::Setting

The exception was triggered by an error during the general preparation of the processing, e.g. an error during initialization of the rasterization backend.
SVG::Rasterize::Exception::Parse

An error occured during parsing (usually of an attribute value). An exception of this class always indicates an inconsistency between validation and parsing of this value and should be reported as a bug.
SVG::Rasterize::Exception::Unsupported

The document (or user) tried to use a feature that is currently unsupported.
SVG::Rasterize::Exception::ParamsValidate

A method parameter did not pass a Params::Validate check.
SVG::Rasterize::Exception::Param

A method parameter passed the Params::Validate check, but is still invalid (an example is that the Params::Validate check only included that the value must be a number, but it also has to be in a certain range which is checked individually later).

Warnings

"Unrecognized init parameter %s."

You have given a parameter to the new method which does not have a corresponding method. The parameter is ignored in that case.
"Unable to load %s: %s. Falling back to SVG::Rasterize::Cairo."

The engine_class you were trying to use for rasterization could not be loaded. SVG::Rasterize then tries to use its default backend SVG::Rasterize::Cairo. If that also fails, it gives up.
"Surface width is 0, nothing to do."

The width of output image evaluates to 0. This value is rounded to an integer number of pixels, therefore this warning does not mean that you have provided an explicit number of 0 (it could also have been e.g. 0.005in at a resolution of 90dpi). In this case, nothing is drawn.
"Surface height is 0, nothing to do."

Like above.

DEPENDENCIES

Class::Accessor, version 0.30 or higher
SVG, version 2.37 or higher
Cairo, version 1.061 or higher

With respect to the module code, the dependency on Cairo is not strict. The code only requires Cairo in case no other rasterization engine is specified (see documentation for details). However, if you do not provide a different backend, which would probably at least require a wrapper written by you, then you cannot do anything without Cairo. Therefore I have included it as a strict dependency. You could take it out of the Makefile.PL if you know what you are doing. However, the distribution will not pass the test suite without Cairo.
Pango, version 1.220 or higher

What has been said about Cairo above is also true for Pango. Both are loaded by SVG::Rasterize::Cairo and that is only loaded if no other backend has been specified.
Params::Validate, version 0.91 or higher
Scalar::Util, version 1.19 or higher
Exception::Class, version 1.29 or higher
Test::More, version 0.86 or higher
Test::Exception, version 0.27 or higher

BUGS AND LIMITATIONS

Bugs

No bugs have been reported. Please report any bugs or feature requests to bug-svg-rasterize at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=SVG-Rasterize. I will be notified, and then you will automatically be notified of progress on your bug as I make changes.

Caveats

`eval BLOCK` and `$SIG{DIE}`

Several methods in this distribution use eval BLOCK statements without setting a local $SIG{__DIE__}. Therefore, a $SIG{__DIE__} installed somewhere else can be triggered by these statements. See die and eval in perlfunc and $^S in perlvar.

Thread safety

I do not know much about threads and how to make a module thread safe. No specific measures have been taken to achieve thread safety of this distribution.

Parameter Checking

SVG::Rasterize uses Params::Validate for parameter validation. However, it currently does not do that as thoroughly as one would wish for. Do not rely on that wrong stuff will not pass unnoticed.

Test Suite

The test suite covers essential features, but is far from exhaustive.

INTERNALS

Regular Expressions

Some regular expressions are used at different locations of the code to validate or extract user input. They are listed in the INTERNALS section because it is not part of the interface where exactly they are used. They are documented for inspection only. They are compiled into other expressions so changing them will probably not achieve what you might expect. The exception to this rule is the PACKAGE_NAME variable. See SVG::Rasterize::Regexes for a full list.

$package_part (internal)
```
  qr/[a-zA-Z][a-zA-Z0-9\_]*/
```
$SVG::Rasterize::Regexes::RE_PACKAGE{p_PACKAGE_NAME}
```
  qr/^$package_part(?:\:\:$package_part)*$/
```
Package names given to methods in this class, namely the engine_class parameters have to match this regular expression. I am not sure which package names exactly are allowed. If you know where in the Perl manpages or the Camel book this is described, please point me to it. If this pattern is too strict for your favourite package name, you can change this variable.

Internal Methods

These methods are just documented for myself. You can read on to satisfy your voyeuristic desires, but be aware of that they might change or vanish without notice in a future version.

_create_engine

Expects a HASH reference as parameter. No validation is performed. The entries width, height, and engine_class are used and expected to be valid if present.
_process_normalize_attributes

Expects a flag (to indicate if normalization is to be performed) and a HASH reference. The second parameter can be false, but if it is true it is expected (without validation) to be a HASH reference. Makes a copy of the hash and returns it after removing (if the flag is true) enclosing white space from each value.
_initial_viewport

Expects two HASH references. The first one is expected to be defined and a HASH reference, but the content can be arbitrary. The second is expected to be validated. Does not return anything.
_angle
```
  $angle = _angle($x1, $y1, $x2, $y2)
  $angle = SVG::Rasterize->_angle($x1, $y1, $x2, $y2)
  $angle = $rasterize->_angle($x1, $y1, $x2, $y2)
```
Expects two vectors and returns the angle between them in rad. No parameter validation is performed. If one of the vectors is 0 (and only if it is exactly 0), undef is returned.
_split_path_data

Expects a path data string. This is expected (without validation) to be defined. Everything else is checked within the method.

Returns a list. The first entry is either 1 or 0 indicating if an error has occured (i.e. if the string is not fully valid). The rest is a list of ARRAY references containing the instructions to draw the path.
_draw_path

Does not take any parameters (i.e. ignores them). Expects the following:
- $self->state is defined and valid.
The rest is handed over to the rasterization backend (which has - nota bene - its expectations.
_draw_rect

Does not take any parameters (i.e. ignores them). Expects the following:
- $self->state is defined and valid.
- $state->node_attributes have been validated.
The rest is handed over to the rasterization backend (which has - nota bene - its expectations.
_draw_circle

Same es _draw_rect.
_draw_ellipse

Same es _draw_rect.
_draw_line

Same es _draw_rect.
_draw_polyline

Same es _draw_path.
_draw_polygon

Same es _draw_path.

FOOTNOTES

[1] Yannis Haralambous: Fonts & Encodings. O'Reilly, 2007.

Tons of information about what the author calls the "digital space for writing".

ACKNOWLEDGEMENTS

This distribution builds heavily on the cairo library and its Perl bindings.

AUTHOR

Lutz Gehlen, <perl at lutzgehlen.de>

LICENSE AND COPYRIGHT

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.

To install SVG::Rasterize, copy and paste the appropriate command in to your terminal.

cpanm

cpanm SVG::Rasterize

CPAN shell

perl -MCPAN -e shell
install SVG::Rasterize

For more information on module installation, please visit the detailed CPAN module installation guide.

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