Adds a webp image to the srcset if available in the media-library.

webpsrcset.php

<?php
/**
 * Adds a webp image to the srcset if available in the media-library.
 *
 * @param string $post_id
 * @param array $args
 * @return string — Image markup.
 */
function abe_get_picture_source( $post_id = 0, $args = [] ): string {
	$post_id = $post_id ?: get_the_ID();

	$defaults = [
		'size' => 'thumbnail',
		'class' => 'src-img',
		'thumb_url' => get_the_post_thumbnail_url( $post_id ),
		'thumb_id' => get_post_thumbnail_id( $post_id ),
		'decor' => false,
	];

	$args = wp_parse_args( $args, $defaults );

	$thumb_url = $args['thumb_url'];
	$thumb_base_url = rtrim( $args['thumb_url'], 'jpengifco' );
	$webp_url = "{$thumb_base_url}webp";

	$thumb_src = wp_get_attachment_image_src( $args['thumb_id'], $args['size'] );

	$upload_dir = wp_upload_dir();

	$replace = [
		home_url( $upload_dir['baseurl'] ),
		$upload_dir['baseurl'],
	];

	$image_abs = str_replace( $replace, '', $webp_url );
	$image_alt = get_the_title( $post_id );
	$image_class = $args['class'];
	$image_width = $thumb_src['1'] ?: '900';
	$image_height = $thumb_src['2'] ?: '900';

	$image_decor = $args['decor'] ? ' aria-hidden="true"' : '';

	$img_src = '';

	if ( file_exists( trailingslashit( $upload_dir['basedir'] ) . $image_abs ) ) {

		$img_src .= "<source srcset='{$webp_url}' alt='{$image_alt}' class='picture-image webp-image {$image_class}' width='{$image_width}' height='{$image_height}' type='image/webp'>";
	}

		$img_src .= "<img src='{$thumb_url}' alt='{$image_alt}' class='picture-image {$image_class}' width='{$image_width}' height='{$image_height}'$image_decor>";

		return $img_src;
}