NAME
Image::Math::Constrain - Scaling math used in image size constraining
(such as for thumbnails)
SYNOPSIS
# Create the math object
my $Math = Image::Math::Constrain->new(64, 48);
# Get the scaling values for an arbitrary image
my $Image = My::Image->load("myimage.jpg");
my $scaling = $Math->constrain($Image->width, $Image->height);
die "Don't need to scale" if $scaling->{scale} = 1;
# Returns the three values as a list when called in array contect
my ($width, $height, $scale) = $Math->constrain(800, 600);
# There are lots of different ways to specify the constrain
# Constrain based on width only
$Math = Image::Math::Constrain->new(100, 0);
# Constrain based on height only
$Math = Image::Math::Constrain->new(0, 100);
# Or you can provide the two values by ARRAY ref
$Math = Image::Math::Constrain->new( [ 64, 48 ] );
# Constrain height and width by the same value
$Math = Image::Math::Constrain->new(100);
# Various string forms to do the same thing
$Math = Image::Math::Constrain->new('constrain(800x600)');
$Math = Image::Math::Constrain->new('300x200');
$Math = Image::Math::Constrain->new('300w200h');
$Math = Image::Math::Constrain->new('100w');
$Math = Image::Math::Constrain->new('100h');
# Serialises back to 'constrain(800x600)'.
# You can use this to store the object if you wish.
my $string = $Math->as_string;
DESCRIPTION
There are a number of different modules and systems that constrain image
sizes, such as thumbnailing. Every one of these independantly implement
the same logic. That is, given a width and/or height constraint, they
check to see if the image is bigger than the constraint, and if so scale
the image down proportionally so that it fits withint the constraints.
Of course, they all do it slightly differnetly, and some do it better
than others.
Image::Math::Constrain has been created to specifically to implement
this logic once, and implement it properly. Any module or script that
does image size constraining or thumbnailing should probably be using
this for it's math.
METHODS
new $width, $height
-head2 new [ $width, $height ]
new $width_and_height
new $string
The "new" constructor takes the dimentions to which you wish to
constrain and creates a new math object.
You can feed a number of different height/width pairs to this object,
and it will returns the scaling you will need to do to shrink the image
down to the constraints, and the final width and height of the image
after scaling, at least one of which should match the constraint.
A value of zero is used to indicate that a dimension should not be
constrained. Thus, "<-"new(400, 0)>> would indicate to constrain the
width to 400 pixels, but to ignore the height (only changing it to keep
the image proportional).
The constraint dimensions can be provided in a number of different
formats. See the Synopsis about for a quick list of these. To stay
compatible with automated constraint generators, you can provide
constrains as zero width and zero height, and the math object will not
attempt to do any scaling, always returning the input width/height, and
a scaling value of 1.
Once created, the object is fully Storable and re-usable and does not
store any state information from a single calculation run.
Returns a new Image::Math::Constrain object, or "undef" if the
constraints have been defined wrongly.
width
The "width" method gets the width constraint for the object.
Returns a positive integer, or zero if there is no width constraint.
height
The "height" method gets the height constrain for the object.
Returns a positive integer, or zero if there is no height constraint.
as_string
The "as_string" method returns the constrain rule as a string in the
format 'constrain(123x123)'. This string form is also supported by the
constructor and so it provides a good way to serialise the constrain
rule, should you ever need to do so.
As this value is not localisable, it should never really be shown to the
user directly, unless you are sure you will never add i18n to your app.
constrain $width, $height
The "constrain" method takes the height and width of an image and
applies the constrain math to them to get the final width, height and
the scaling value needed in order to get the your image from it's
current size to the final size.
When called in array context, returns the new dimensions and scaling
value as a list, as in the following.
my ($width, $height, $scale) = $Math->constrain(800, 600);
When called in scalar context, it returns a reference to a hash
containing the keys 'width', 'height', and 'scale'.
my $hash = $Math->constrain(800, 600);
print "New Width : $hash->{width}\n";
print "New Height : $hash->{height}\n";
print "Scaling By : $hash->{scalar}\n";
Having been created correctly, the object will only return an error if
the width and height arguments are not correct (are not positive
integers).
In list context, returns a null list, so all three values will be
"undef".
In scalar context, just returns "undef".
TO DO
- Write more special-case unit tests
SUPPORT
Bugs should always be submitted via the CPAN bug tracker
For other issues, contact the maintainer
AUTHORS
Adam Kennedy (Maintainer), , cpan@ali.as
Thank you to Phase N () for permitting the open
sourcing and release of this distribution.
COPYRIGHT
Copyright (c) 2004 Adam Kennedy. All rights reserved. This program is
free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
The full text of the license can be found in the LICENSE file included
with this module.