Question

wordpress has a good support for images in general.

to get new image sizes, one would just add some functions like :

add_theme_support( 'post-thumbnails' ); //thumnails
set_post_thumbnail_size( 200, 120, true ); // Normal post thumbnails
add_image_size( 'single-post-thumbnail', 400, 300,False ); // single-post-test
add_image_size( 'tooltip', 100, 100, true ); // Tooltips thumbnail size
/// and so on and so on 

my question is :

How can someone make those functions act in a dynamic manner , meaning that those sizes will be calculated on upload ?

for example – If I upload an image of 3000×4000 px – I would like my image sizes to be :

 add_image_size( 'half', 50%, 350%, False ); // Half the original
 add_image_size( 'third', 30%, 30%, true ); // One Third the original

Is there a way to do that ? where can I hook for that ?
Those image sizes are used registered in many functions –
Can someone think of an Uber-creative way to achieve that ?

Answer 1

You can use wp_get_attachment_image_src to get downsized images of an attachement, in you case you only need to specify add_theme_support( 'post-thumbnails' ) in your functions.php file then in your template do the following:

$id = get_post_thumbnail_id($post->ID)
$orig = wp_get_attachment_image_src($id)
$half = wp_get_attachment_image_src($id, array($orig[1] / 2, orig[2] / 2))
$third = wp_get_attachment_image_src($id, array($orig[1] / 3, orig[2] / 3))
etc...