wp_calculate_image_srcset( int[] $size_array, string $image_src, array $image_meta, int $attachment_id = 0 ): string|false

Compatibility

Present in every tracked release (6.7.7 to 7.1.0), and compiles on PHP 7.4 through 8.6-dev.

Parameters

$size_arrayint[]

An array of width and height values.

• $0int

  The width in pixels.

• $1int

  The height in pixels.

$image_srcstring

The 'src' of the image.

$image_metaarray

The image meta data as returned by 'wp_get_attachment_metadata()'.

$attachment_idintoptional

The image attachment ID. Default 0.Default: 0

Return value

string|false

The 'srcset' attribute value. False on error or when only one source exists.

Performance profile

How much work a call to wp_calculate_image_srcset() does, and what it touches: the algorithmic scaling, the Zend instruction count per call across PHP versions, the hooks it hands control to, and the core code that calls it. Measured from the compiled opcodes, not a stopwatch, so every number is identical on any machine running the same PHP version, and every function in core is ranked by cost.

Cost class

Light

Touches nothing outside its own arguments.

Scaling

Scales with input

The body loops, so the work grows with what you pass in.

Instructions

15–138

Executed per call on PHP 8.5, depending on the branch taken. The body compiles to 204.

Plugin surface

3 hooks

Third-party callbacks on 'wp_calculate_image_srcset_meta', 'max_srcset_image_width', 'wp_calculate_image_srcset' run inside this call, and their cost is not bounded by anything here.

Called by

4

4 places in core call this, so the cost is paid more often than your own code shows.

What it touches

• hookthird-party callbacksapply_filters()called directly

Further down the call graph this can also reach option, cache, serialize, query and transient. Those are the worst case, several calls deep and usually down an error path, not what a normal call pays.

What one call costs · 14 distinct outcomes

One number would be a lie: the work depends on which branch runs. These are every distinct cost wp_calculate_image_srcset() can have, taken from its control-flow graph on PHP 8.5.

Hooks and filters fired · 3

3 hooks fire while wp_calculate_image_srcset() runs, in this order:

1. 1
   apply_filters( wp_calculate_image_srcset_meta )filterline 1379 (+16 into the body)

   Pre-filters the image meta to be able to fix inconsistencies in the stored data.

2. 2
   apply_filters( max_srcset_image_width )filterline 1464 (+101 into the body)

   Filters the maximum image width to be included in a 'srcset' attribute.

3. 3
   apply_filters( wp_calculate_image_srcset )filterline 1551 (+188 into the body)

   Filters an image's 'srcset' sources.

Uses · 10

• apply_filters()Calls the callback functions that have been added to a filter hook.
• wp_basename()i18n-friendly version of basename().
• str_contains()Polyfill for `str_contains()` function added in PHP 8.0.
• _wp_get_attachment_relative_path()Gets the attachment path relative to the upload directory.
• trailingslashit()Appends a trailing slash.
• wp_get_upload_dir()Retrieves uploads directory information.
• is_ssl()Determines if SSL is used.
• str_starts_with()Polyfill for `str_starts_with()` function added in PHP 8.0.
• set_url_scheme()Sets the scheme for a URL.
• wp_image_matches_ratio()Helper function to test if aspect ratios for two images match.

Used by · 4

• get_header_image_tag()Creates image tag markup for a custom header image.
• wp_get_attachment_image()Gets an HTML img element representing an image attachment.
• wp_get_attachment_image_srcset()Retrieves the value for an image attachment's 'srcset' attribute.
• wp_image_add_srcset_and_sizes()Adds 'srcset' and 'sizes' attributes to an existing 'img' element.

Source code

View on Trac ↗View on GitHub ↗

1363function wp_calculate_image_srcset( $size_array, $image_src, $image_meta, $attachment_id = 0 ) {1364	/**1365	 * Pre-filters the image meta to be able to fix inconsistencies in the stored data.1366	 *1367	 * @since 4.5.01368	 *1369	 * @param array  $image_meta    The image meta data as returned by 'wp_get_attachment_metadata()'.1370	 * @param int[]  $size_array    {1371	 *     An array of requested width and height values.1372	 *1373	 *     @type int $0 The width in pixels.1374	 *     @type int $1 The height in pixels.1375	 * }1376	 * @param string $image_src     The 'src' of the image.1377	 * @param int    $attachment_id The image attachment ID or 0 if not supplied.1378	 */1379	$image_meta = apply_filters( 'wp_calculate_image_srcset_meta', $image_meta, $size_array, $image_src, $attachment_id );1380 1381	if ( empty( $image_meta['sizes'] ) || ! isset( $image_meta['file'] ) || strlen( $image_meta['file'] ) < 4 ) {1382		return false;1383	}1384 1385	$image_sizes = $image_meta['sizes'];1386 1387	// Get the width and height of the image.1388	$image_width  = (int) $size_array[0];1389	$image_height = (int) $size_array[1];1390 1391	// Bail early if error/no width.1392	if ( $image_width < 1 ) {1393		return false;1394	}1395 1396	$image_basename = wp_basename( $image_meta['file'] );1397 1398	/*1399	 * WordPress flattens animated GIFs into one frame when generating intermediate sizes.1400	 * To avoid hiding animation in user content, if src is a full size GIF, a srcset attribute is not generated.1401	 * If src is an intermediate size GIF, the full size is excluded from srcset to keep a flattened GIF from becoming animated.1402	 */1403	if ( ! isset( $image_sizes['thumbnail']['mime-type'] ) || 'image/gif' !== $image_sizes['thumbnail']['mime-type'] ) {1404		$image_sizes[] = array(1405			'width'  => $image_meta['width'],1406			'height' => $image_meta['height'],1407			'file'   => $image_basename,1408		);1409	} elseif ( str_contains( $image_src, $image_meta['file'] ) ) {1410		return false;1411	}1412 1413	// Retrieve the uploads sub-directory from the full size image.1414	$dirname = _wp_get_attachment_relative_path( $image_meta['file'] );1415 1416	if ( $dirname ) {1417		$dirname = trailingslashit( $dirname );1418	}1419 1420	$upload_dir    = wp_get_upload_dir();1421	$image_baseurl = trailingslashit( $upload_dir['baseurl'] ) . $dirname;1422 1423	/*1424	 * If currently on HTTPS, prefer HTTPS URLs when we know they're supported by the domain1425	 * (which is to say, when they share the domain name of the current request).1426	 */1427	if ( is_ssl() && ! str_starts_with( $image_baseurl, 'https' ) ) {1428		/*1429		 * Since the `Host:` header might contain a port, it should1430		 * be compared against the image URL using the same port.1431		 */1432		$parsed = parse_url( $image_baseurl );1433		$domain = $parsed['host'] ?? '';1434 1435		if ( isset( $parsed['port'] ) ) {1436			$domain .= ':' . $parsed['port'];1437		}1438 1439		if ( $_SERVER['HTTP_HOST'] === $domain ) {1440			$image_baseurl = set_url_scheme( $image_baseurl, 'https' );1441		}1442	}

Changelog

Introduced in 4.4.0. Unchanged from 6.7.7 through 7.1.0.

1. 6.7.7
2. 6.8.8
3. 6.9.7
4. 7.0.4
5. 7.1.0

Signature, return type and hooks compared across 5 parsed releases.

About this page

Parsed data

Generated from the wordpress-develop 7.0.4 tag, from src/wp-includes/media.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.

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