Implemented interlace support for GD, Imagick, and Gmagick.

[anthonysterling]

I thought it best to raise my own PR for Interlace Support given PR #185 has been dormant for a month or so.

Apologies @vchrm.

This PR adds interlace support for the GD, Imagick, and Gmagick implementations. It still requires updated documentation and tests, as such, I would really appreciate some guidance on the best approach to add tests for this functionality.

I'm looking forward to having someone review this.

Thanks everyone.

Anthony.

[romainneutron]

what about defining it static like at https://github.com/avalanche123/Imagine/blob/develop/lib/Imagine/Imagick/Image.php#L673 ?

[anthonysterling]

Sure, I'm happy to do that to help maintain consistency. :)

Thanks.

[anthonysterling]

I did notice that the Imagick and Gmagick objects call the interlace types scheme, I wonder if it's worth changing $type to scheme too.

ImageInterface::interlace($scheme);

[anthonysterling]

Strange, if I use GD to create a set of interlaced images with:-

<?php
require_once __DIR__ . '/vendor/autoload.php';
$imagine = new Imagine\Gd\Imagine();
$image = $imagine->open('fixture.jpeg');
$image->interlace(Imagine\Image\ImageInterface::INTERLACE_LINE);
$image->save('interlaced.gif');
$image->save('interlaced.jpg');
$image->save('interlaced.png');

If I then use ImageMagick's identify utility to detect interlacing on the resulting images, I get a negative result for interlaced.gif.

➜  imagine-test  identify -verbose interlaced.gif | grep Interlace 
  Interlace: None
➜  imagine-test  identify -verbose interlaced.jpg | grep Interlace
  Interlace: JPEG
➜  imagine-test  identify -verbose interlaced.png | grep Interlace
  Interlace: PNG

I'll investigate further.

[avalanche123]

Thanks, @anthonysterling, I'm merging this in. Sorry for the lack of responses, I'm quite busy these couple of weeks