wp_calculate_image_sizes() WP 4.4.0

Creates a 'sizes' attribute value for an image.

Hooks in function

Return

String/true/false. A valid source size value for use in a 'sizes' attribute or false.

Usage

wp_calculate_image_sizes( $size, $image_src, $image_meta, $attachment_id );

$size(array/string) (required)

Image size to retrieve. Accepts any valid image size, or an array of width and height values in pixels (in that order).
Default: 'medium'

$image_src(string)

The URL to the image file.
Default: null

$image_meta(array)

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

$attachment_id(int)

Image attachment ID. Either $image_meta or $attachment_id is needed when using the image size name as argument for $size.
Default: 0

Code of wp calculate image sizes: wp-includes/media.php ^{WP 5.2.2}

<?php
function wp_calculate_image_sizes( $size, $image_src = null, $image_meta = null, $attachment_id = 0 ) {
	$width = 0;

	if ( is_array( $size ) ) {
		$width = absint( $size[0] );
	} elseif ( is_string( $size ) ) {
		if ( ! $image_meta && $attachment_id ) {
			$image_meta = wp_get_attachment_metadata( $attachment_id );
		}

		if ( is_array( $image_meta ) ) {
			$size_array = _wp_get_image_size_from_meta( $size, $image_meta );
			if ( $size_array ) {
				$width = absint( $size_array[0] );
			}
		}
	}

	if ( ! $width ) {
		return false;
	}

	// Setup the default 'sizes' attribute.
	$sizes = sprintf( '(max-width: %1$dpx) 100vw, %1$dpx', $width );

	/**
	 * Filters the output of 'wp_calculate_image_sizes()'.
	 *
	 * @since 4.4.0
	 *
	 * @param string       $sizes         A source size value for use in a 'sizes' attribute.
	 * @param array|string $size          Requested size. Image size or array of width and height values
	 *                                    in pixels (in that order).
	 * @param string|null  $image_src     The URL to the image file or null.
	 * @param array|null   $image_meta    The image meta data as returned by wp_get_attachment_metadata() or null.
	 * @param int          $attachment_id Image attachment ID of the original image or 0.
	 */
	return apply_filters( 'wp_calculate_image_sizes', $sizes, $size, $image_src, $image_meta, $attachment_id );
}