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Wiele osób boryka się z problemem zmiany rozmiaru obrazów „w locie”, zarówno przy projektowaniu styli, pluginów czy innych dodatków do silnika WordPress.

Do tego celu warto użyć powszechnie znanej w internecie funkcji vt_resize(), która bezproblemowo ułatwi nam wygenerowanie obrazów dokładnie w takim rozmiarze, w jakim tego chcemy.

Na początek kod funkcji należy dodać do pliku functions.php naszego stylu, bądź do pliku głównego lub biblioteki wtyczki.

if ( !function_exists( 'vt_resize') ) {
function vt_resize( $attach_id = null, $img_url = null, $width, $height, $crop = false ) {
// this is an attachment, so we have the ID
if ( $attach_id ) {
$image_src = wp_get_attachment_image_src( $attach_id, 'full' );
$file_path = get_attached_file( $attach_id );
// this is not an attachment, let's use the image url
} else if ( $img_url ) {
$file_path = parse_url( $img_url );
$file_path = $_SERVER['DOCUMENT_ROOT'] . $file_path['path'];
// Look for Multisite Path
if(file_exists($file_path) === false){
global $blog_id;
$file_path = parse_url( $img_url );
if (preg_match("/files/", $file_path['path'])) {
$path = explode('/',$file_path['path']);
foreach($path as $k=>$v){
if($v == 'files'){
$path[$k-1] = 'wp-content/blogs.dir/'.$blog_id;
}
}
$path = implode('/',$path);
}
$file_path = $_SERVER['DOCUMENT_ROOT'].$path;
}
//$file_path = ltrim( $file_path['path'], '/' );
//$file_path = rtrim( ABSPATH, '/' ).$file_path['path'];
$orig_size = getimagesize( $file_path );
$image_src[0] = $img_url;
$image_src[1] = $orig_size[0];
$image_src[2] = $orig_size[1];
}
$file_info = pathinfo( $file_path );
// check if file exists
$base_file = $file_info['dirname'].'/'.$file_info['filename'].'.'.$file_info['extension'];
if ( !file_exists($base_file) )
return;
$extension = '.'. $file_info['extension'];
// the image path without the extension
$no_ext_path = $file_info['dirname'].'/'.$file_info['filename'];
$cropped_img_path = $no_ext_path.'-'.$width.'x'.$height.$extension;
// checking if the file size is larger than the target size
// if it is smaller or the same size, stop right here and return
if ( $image_src[1] > $width ) {
// the file is larger, check if the resized version already exists (for $crop = true but will also work for $crop = false if the sizes match)
if ( file_exists( $cropped_img_path ) ) {
$cropped_img_url = str_replace( basename( $image_src[0] ), basename( $cropped_img_path ), $image_src[0] );
$vt_image = array (
'url' => $cropped_img_url,
'width' => $width,
'height' => $height
);
return $vt_image;
}
// $crop = false or no height set
if ( $crop == false OR !$height ) {
// calculate the size proportionaly
$proportional_size = wp_constrain_dimensions( $image_src[1], $image_src[2], $width, $height );
$resized_img_path = $no_ext_path.'-'.$proportional_size[0].'x'.$proportional_size[1].$extension;
// checking if the file already exists
if ( file_exists( $resized_img_path ) ) {
$resized_img_url = str_replace( basename( $image_src[0] ), basename( $resized_img_path ), $image_src[0] );
$vt_image = array (
'url' => $resized_img_url,
'width' => $proportional_size[0],
'height' => $proportional_size[1]
);
return $vt_image;
}
}
// check if image width is smaller than set width
$img_size = getimagesize( $file_path );
if ( $img_size[0] <= $width ) $width = $img_size[0];
// Check if GD Library installed
if (!function_exists ('imagecreatetruecolor')) {
echo 'GD Library Error: imagecreatetruecolor does not exist - please contact your webhost and ask them to install the GD library';
return;
}
// no cache files - let's finally resize it
$new_img_path = image_resize( $file_path, $width, $height, $crop );			
$new_img_size = getimagesize( $new_img_path );
$new_img = str_replace( basename( $image_src[0] ), basename( $new_img_path ), $image_src[0] );
// resized output
$vt_image = array (
'url' => $new_img,
'width' => $new_img_size[0],
'height' => $new_img_size[1]
);
return $vt_image;
}
// default output - without resizing
$vt_image = array (
'url' => $image_src[0],
'width' => $width,
'height' => $height
);
return $vt_image;
}
}

Teraz możemy skorzystać z naszej funkcji w stylu lub pluginie. Przykład użycia na moim przykładzie, wyświetli wszystkie obrazy skojarzone z postem.

$media = get_attached_media( 'image' );
foreach($media as $m)
{
$image_attributes = wp_get_attachment_image_src( $m->ID, 'small', false );
$image = vt_resize('', $image_attributes[0], 700, 300, true);
echo "\"\"";
}