1,
'data-srcset' => 1,
'data-sizes' => 1,
'class' => 1,
) );
$allowed_tags['img'] = $img_attributes;
return $allowed_tags;
}
/**
* Find image elements that should be lazy-loaded.
*
* @param object $content The content.
* @return object
*/
function pixigo_add_image_placeholders( $content ) {
// Don't lazyload for feeds, previews.
if ( is_feed() || is_preview() ) {
return $content;
}
// Don't lazy-load if the content has already been run through previously.
if ( false !== strpos( $content, 'data-src' ) ) {
return $content;
}
// Find all ![]()
elements via regex, add lazy-load attributes.
$content = preg_replace_callback( '#<(img)([^>]+?)(>(.*?)|[\/]?>)#si', 'pixigo_process_image', $content );
return $content;
}
/**
* Returns true when a given string of classes contains a class signifying image
* should not be lazy-loaded
*
* @param string $classes A string of space-separated classes.
* @return bool
*/
function pixigo_should_skip_image_with_blacklisted_class( $classes ) {
$blacklisted_classes = array(
'skip-lazy',
);
foreach ( $blacklisted_classes as $class ) {
if ( false !== strpos( $classes, $class ) ) {
return true;
}
}
return false;
}
/**
* Processes images in content by acting as the preg_replace_callback.
*
* @param array $matches ![]()
element to be altered.
*
* @return string The image with updated lazy attributes
*/
function pixigo_process_image( $matches ) {
$old_attributes_str = $matches[2];
$old_attributes_kses_hair = wp_kses_hair( $old_attributes_str, wp_allowed_protocols() );
if ( empty( $old_attributes_kses_hair['src'] ) ) {
return $matches[0];
}
$old_attributes = pixigo_flatten_kses_hair_data( $old_attributes_kses_hair );
$new_attributes = pixigo_process_image_attributes( $old_attributes );
// If we didn't add lazy attributes, just return the original image source.
if ( empty( $new_attributes['data-src'] ) ) {
return $matches[0];
}
$new_attributes_str = pixigo_build_attributes_string( $new_attributes );
return sprintf( '![]()
', $new_attributes_str, $matches[0] );
}
/**
* Given an array of image attributes, updates the `src`, `srcset`, and `sizes` attributes so
* that they load lazily.
*
* @param array $attributes Attributes of the current ![]()
element.
*
* @return array The updated image attributes array with lazy load attributes.
*/
function pixigo_process_image_attributes( $attributes ) {
if ( empty( $attributes['src'] ) ) {
return $attributes;
}
if ( ! empty( $attributes['class'] ) && pixigo_should_skip_image_with_blacklisted_class( $attributes['class'] ) ) {
return $attributes;
}
$old_attributes = $attributes;
// Add the lazy class to the img element.
$attributes['class'] = pixigo_set_lazy_class( $attributes );
// Set placeholder and lazy-src.
$attributes['src'] = pixigo_get_placeholder_image();
// Set data-src to the original source uri.
$attributes['data-src'] = $old_attributes['src'];
// Process `srcset` attribute.
if ( ! empty( $attributes['srcset'] ) ) {
$attributes['data-srcset'] = $old_attributes['srcset'];
unset( $attributes['srcset'] );
}
// Process `sizes` attribute.
if ( ! empty( $attributes['sizes'] ) ) {
$attributes['data-sizes'] = $old_attributes['sizes'];
unset( $attributes['sizes'] );
}
return $attributes;
}
/**
* Append a `lazy` class to ![]()
elements for lazy-loading.
*
* @param array $attributes ![]()
element attributes.
* @return string
*/
function pixigo_set_lazy_class( $attributes ) {
if ( array_key_exists( 'class', $attributes ) ) {
$classes = $attributes['class'];
$classes .= ' lazy';
} else {
$classes = 'lazy';
}
return $classes;
}
/**
* Set the placeholder image.
*
* @return string The URL to the placeholder image.
*/
function pixigo_get_placeholder_image() {
return get_theme_file_uri( '/images/placeholder.svg' );
}
/**
* Flatten attribute list into string.
*
* @param array $attributes Array of attributes.
* @return string $flattened_attributes
*/
function pixigo_flatten_kses_hair_data( $attributes ) {
$flattened_attributes = array();
foreach ( $attributes as $name => $attribute ) {
$flattened_attributes[ $name ] = $attribute['value'];
}
return $flattened_attributes;
}
/**
* Build string of new attributes to be returned to the ![]()
element.
*
* @param array $attributes Array of attributes.
* @return string
*/
function pixigo_build_attributes_string( $attributes ) {
$string = array();
foreach ( $attributes as $name => $value ) {
if ( '' === $value ) {
$string[] = sprintf( '%s', $name );
} else {
$string[] = sprintf( '%s="%s"', $name, esc_attr( $value ) );
}
}
return implode( ' ', $string );
}
/**
* Enqueue and defer lazyload script.
*/
function pixigo_enqueue_assets() {
wp_enqueue_script( 'pixigo-lazy-load-images', get_theme_file_uri( '/pluggable/lazyload/js/lazyload.js' ), array(), '20151215', false );
wp_script_add_data( 'pixigo-lazy-load-images', 'defer', true );
}