Drupal 7 Module Development

Working with Files and Images
This is about as simple as Drupal hooks get, especially given everything that
has already been covered previously in this chapter. Our implementation of
hook_image_default_styles() returns $styles, an associative array of image
style definitions, keyed on a unique string. This string will act as the style's name
and will be displayed on the image styles admin page.
Each style definition is a set of image effects, along with their effect-specific settings,
if any. The keys this array can contain are as follows:
• name: The unique name of the effect we're implementing.
• data: An optional array of configuration settings. These should be keyed on
the same text string that are used in the form callback defined by the effect.
Note that default values defined in the form callback will NOT be honored if
you do not include them. You will have to enter them by hand here.
• weight: An optional weight, used to control effect ordering when multiple
effects are included in a single style. As is Drupal standard, lower weights
'float to the top' and higher weights 'sink to the bottom'.
That is really all there is to it. If you load the image styles listing, you will now see
your style listed (you may need to clear the Drupal cache first).
One nice aspect about image styles defined by a module is that they are protected
from being changed or modified by end users (or accidentally broken by the
developers themselves). This is implemented in two ways. First, in order to modify
the settings of a style implemented through hook_image_default_styles(), you
must specifically take the extra step of saying you want to override it. Take a look
at the following screen:
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