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Media: Ensure images have dimensions to reduce layout shift and facilitate lazy-loading. 

This changeset ensures that attachment images which are inserted without `width` and `height` attributes still receive them in the frontend, to reduce cumulative layout shift. Adding the dimensions happens as part of the logic for adding `srcset` and `sizes` attributes, which already assume the specific width and height of the respective image.

Images are now only lazy-loaded if they have `width` and `height` attributes present. While missing these attributes itself is what causes layout shifts, lazy-loading such images can make this problem more apparent to the user.

Props adamsilverstein, westonruter.
Fixes #50367. See #44427.


git-svn-id: https://develop.svn.wordpress.org/trunk@48170 602fd350-edb4-49c9-b593-d223f7449a82
This commit is contained in:
Felix Arntz 2020-06-25 18:43:25 +00:00
parent 886b254ec5
commit 9568134d7b
2 changed files with 43 additions and 18 deletions
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30
src/wp-includes/media.php
View File

@ -1495,6 +1495,7 @@ function wp_calculate_image_sizes( $size, $image_src = null, $image_meta = null,
* Adds 'srcset' and 'sizes' attributes to an existing 'img' element.
*
* @since 4.4.0
* @since 5.5.0 `width` and `height` are now added if not already present.
*
* @see wp_calculate_image_srcset()
* @see wp_calculate_image_sizes()
@ -1525,6 +1526,8 @@ function wp_image_add_srcset_and_sizes( $image, $image_meta, $attachment_id ) {
return $image;
}
$attr = '';
$width = preg_match( '/ width="([0-9]+)"/', $image, $match_width ) ? (int) $match_width[1] : 0;
$height = preg_match( '/ height="([0-9]+)"/', $image, $match_height ) ? (int) $match_height[1] : 0;
@ -1547,10 +1550,13 @@ function wp_image_add_srcset_and_sizes( $image, $image_meta, $attachment_id ) {
}
}
}
}
if ( ! $width || ! $height ) {
return $image;
if ( ! $width || ! $height ) {
return $image;
}
// Add width and height if not present.
$attr .= ' ' . trim( image_hwstring( $width, $height ) );
}
$size_array = array( $width, $height );
@ -1567,17 +1573,19 @@ function wp_image_add_srcset_and_sizes( $image, $image_meta, $attachment_id ) {
if ( $srcset && $sizes ) {
// Format the 'srcset' and 'sizes' string and escape attributes.
$attr = sprintf( ' srcset="%s"', esc_attr( $srcset ) );
$attr .= sprintf( ' srcset="%s"', esc_attr( $srcset ) );
if ( is_string( $sizes ) ) {
$attr .= sprintf( ' sizes="%s"', esc_attr( $sizes ) );
}
// Add 'srcset' and 'sizes' attributes to the image markup.
$image = preg_replace( '/<img ([^>]+?)[\/ ]*>/', '<img $1' . $attr . ' />', $image );
}
return $image;
if ( empty( $attr ) ) {
return $image;
}
// Add extra attributes to the image markup.
return preg_replace( '/<img ([^>]+?)[\/ ]*>/', '<img $1' . $attr . ' />', $image );
}
/**
@ -1714,6 +1722,12 @@ function wp_img_tag_add_loading_attr( $image, $context ) {
$value = 'lazy';
}
// Images should have dimension attributes for the `loading` attribute
// to be added.
if ( false === strpos( $image, ' width=' ) || false === strpos( $image, ' height=' ) ) {
return $image;
}
$quote = null;
// Check if the img tag is valid (has `src` attribute) and get the quote character.

31
tests/phpunit/tests/media.php
View File

@ -1963,6 +1963,7 @@ EOF;
/**
* @ticket 33641
* @ticket 50367
*/
function test_wp_filter_content_tags() {
$image_meta = wp_get_attachment_metadata( self::$large_id );
@ -1982,10 +1983,12 @@ EOF;
$img_xhtml = str_replace( ' />', '/>', $img );
$img_html5 = str_replace( ' />', '>', $img );
$hwstring = image_hwstring( $size_array[0], $size_array[1] );
// Manually add srcset and sizes to the markup from get_image_tag().
$respimg = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img );
$respimg_no_size_in_class = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img_no_size_in_class );
$respimg_no_width_height = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img_no_width_height );
$respimg_no_width_height = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $hwstring . $srcset . ' ' . $sizes . ' />', $img_no_width_height );
$respimg_with_sizes_attr = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $srcset . ' />', $img_with_sizes_attr );
$respimg_xhtml = preg_replace( '|<img ([^>]+)/>|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img_xhtml );
$respimg_html5 = preg_replace( '|<img ([^>]+)>|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img_html5 );
@ -1997,7 +2000,7 @@ EOF;
<p>Image, no size class. Should have srcset and sizes.</p>
%2$s
<p>Image, no width and height attributes. Should have srcset and sizes (from matching the file name).</p>
<p>Image, no width and height attributes. Should have width, height, srcset and sizes (from matching the file name).</p>
%3$s
<p>Image, no attachment ID class. Should NOT have srcset and sizes.</p>
@ -2530,12 +2533,18 @@ EOF;
/**
* @ticket 44427
* @ticket 50367
*/
function test_wp_lazy_load_content_media() {
$img = get_image_tag( self::$large_id, '', '', '', 'medium' );
$img_xhtml = str_replace( ' />', '/>', $img );
$img_html5 = str_replace( ' />', '>', $img );
$iframe = '<iframe src="https://www.example.com"></iframe>';
$image_meta = wp_get_attachment_metadata( self::$large_id );
$size_array = $this->_get_image_size_array_from_meta( $image_meta, 'medium' );
$img = get_image_tag( self::$large_id, '', '', '', 'medium' );
$img_xhtml = str_replace( ' />', '/>', $img );
$img_html5 = str_replace( ' />', '>', $img );
$img_no_width_height = str_replace( ' width="' . $size_array[0] . '"', '', $img );
$img_no_width_height = str_replace( ' height="' . $size_array[1] . '"', '', $img_no_width_height );
$iframe = '<iframe src="https://www.example.com"></iframe>';
$lazy_img = wp_img_tag_add_loading_attr( $img, 'test' );
$lazy_img_xhtml = wp_img_tag_add_loading_attr( $img_xhtml, 'test' );
@ -2551,13 +2560,15 @@ EOF;
%2$s
<p>Image, HTML 5.0 style.</p>
%3$s
<p>Image, with pre-existing "loading" attribute.</p>
<p>Image, with pre-existing "loading" attribute. Should not be modified.</p>
%4$s
<p>Image, without dimension attributes. Should not be modified.</p>
%5$s
<p>Iframe, standard. Should not be modified.</p>
%4$s';
%6$s';
$content_unfiltered = sprintf( $content, $img, $img_xhtml, $img_html5, $iframe, $img_eager );
$content_filtered = sprintf( $content, $lazy_img, $lazy_img_xhtml, $lazy_img_html5, $iframe, $img_eager );
$content_unfiltered = sprintf( $content, $img, $img_xhtml, $img_html5, $img_eager, $img_no_width_height, $iframe );
$content_filtered = sprintf( $content, $lazy_img, $lazy_img_xhtml, $lazy_img_html5, $img_eager, $img_no_width_height, $iframe );
// Do not add srcset and sizes.
add_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );