[wp-hackers] Replacing image_resize() function?

Peter Westwood peter.westwood at ftwr.co.uk
Wed Apr 8 17:19:52 GMT 2009

On 8 Apr 2009, at 17:40, Raul Peixoto wrote:

> Hi there!
> I'm new to this list, so it will be the first time writing to this  
> list, so I hope to enjoy my time here!
> I'm working on a way to replace the image_resize() function, inside  
> wp-includes/media.php and I need some advice regarding this...
> Wordpress allows me to crop, or even generate new image sizes (with  
> a proper hook into the additional_image_sizes function), however I'm  
> working on a project that requires me to rewrite the image_resize  
> function...
> Why is that?
> Well, I need to resize all images to an exact specific size (let's  
> say 120x90 for thumbnail size, and 250x125 for medium size) but I  
> need to do this without cropping. So the only way is to resize and  
> then add a margin to comply with the desired size.
> I have created the new function and named it sp_image_resize.
> Hacking the core files:
> Now the way I got this to work was by hacking into /wp-includes/ 
> media.php, inside function: image_make_intermediate_size, around  
> line 412
> change: $resized_file = image_resize($file, $width, $height, $crop);
> to: $resized_file = sp_image_resize($file, $width, $height, $crop);
> So are there any ideas to replace this function without hacking the  
> core directly?
> ==
> I tried to add_filter( 'image_resize', 'sp_image_resize', 1, 4 );  
> but it doesn't work.
> I also tried to replace the image_make_intermediate_size the same  
> way but with no success.
> Can someone help?

There is not currently a simple way to catch all use cases of  

Depending on which image_resize calls you are trying to affect you  
could probably use the hooks in wp_generate_attachment_metadata

You can filter the sizes in generates using the   
'intermediate_image_sizes' filter and return an empty array to stop  
WordPress doing the resize itself.

You would then do your resizing on the  
'wp_generate_attachment_metadata' filter and populate the $metadata  
array with the extra info.

It looks like for a future proof solution you will need a new hook in  
image_resize to allow you to take over the function.

Please create a ticket on trac with a suggestion and some example  
plugin code which uses the suggested hook and I will make sure this  
makes it into 2.8 - you should then be able to backport that change to  
your current 2.7.1 install and not lose the functionality on upgrade.

Peter Westwood
http://blog.ftwr.co.uk | http://westi.wordpress.com
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