Introduction

Retrieving the original image

The first step is to retrieve the original image, the one you address.

In order to retrieve such an image, there are so-called DataLoader those implement the Liip\ImagineBundle\Binary\Loader\LoaderInterface. Those loaders are typically managed by the DataManager and automatically wired with it, using dependency injection.

How a specific DataLoader retrieves the image is up to the loader. The default is to read a file from the local filesystem. This is implemented by the Liip\ImagineBundle\Binary\Loader\FileSystemLoader, which is configured as the default loader. You could also create a random image on the fly using drawing utilities, or read a binary stream from any stream registered.

The most important parts about those DataLoaders:

1. They find a single image based on a given identifier.
2. They return a ready-to-use Imagine\Image\ImageInterface.

Check out the chapter about data loaders to learn more about them.

Apply filters on the original image

Now, that we fetched an image, we can alter the image in any way. You can create a resized version, a thumbnail, add a watermark, convert it to gray-scale, resample the image, change its resolution ... you get the idea. Any alteration is called a Filter, derived from the naming within the Imagine library.

The responsibility of applying such a filter as bound to a FilterLoader, which are typically managed by the FilterManager. Those FilterLoader implement the Liip\ImagineBundle\Imagine\Filter\Loader\LoaderInterface. The FilterManager is aware of so-called filter_sets. A filter set may define multiple filters to be applied on the result of each predecessor.

The filter has one objective: Apply itself on the provided image (loaded by the DataLoader). It receives options to configure the actual result of it, to customize the outcome.

Check out the chapter about filters to learn more about them.

Cache the filtered image

The filtered - to be cached - image is the image which results after applying all filters within a filter set.

In order to not apply each filter again on the same image, which will by most means result in the same filtered image, this result will be cached. This caching is managed by the CacheManager which manages all so-called CacheResolver.

The default CacheResolver is the WebPathResolver, which will cache the image in the web directory as a static file, so the web server won't call the application stack anymore on those images. The images will be created upon first request and will remain in their static cached version until removed.

A CacheResolver implements the Liip\ImagineBundle\Imagine\Cache\Resolver\ResolverInterface.

It handles the so-called path, which is the identifier you use, when addressing the original image, e.g. in your template. This path relates to the path used in the DataLoader.

The responsibilities of the CacheResolver are:

1. to resolve a given path into a Response, if possible,
2. store given content under a given path to be resolved later,
3. generate an URI to address the cached image directly,
4. remove a cached image.

Check out the chapter about cache resolvers to learn more about them.