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| 1 | <?php |
| 2 | |
| 3 | namespace MobileFrontend\Transforms; |
| 4 | |
| 5 | use DOMDocument; |
| 6 | use DOMElement; |
| 7 | use MobileFrontend\Transforms\Utils\HtmlClassUtils; |
| 8 | use MobileFrontend\Transforms\Utils\HtmlStyleUtils; |
| 9 | use Wikimedia\Parsoid\Utils\DOMCompat; |
| 10 | |
| 11 | class LazyImageTransform implements IMobileTransform { |
| 12 | |
| 13 | /** |
| 14 | * Do not lazy load images smaller than this size (in pixels) |
| 15 | */ |
| 16 | private const SMALL_IMAGE_DIMENSION_THRESHOLD_IN_PX = 50; |
| 17 | |
| 18 | /** |
| 19 | * Do not lazy load images smaller than this size (in relative to x-height of the current font) |
| 20 | */ |
| 21 | private const SMALL_IMAGE_DIMENSION_THRESHOLD_IN_EX = 10; |
| 22 | |
| 23 | /** |
| 24 | * Whether to skip the loading of small images |
| 25 | * @var bool |
| 26 | */ |
| 27 | protected $skipSmall; |
| 28 | |
| 29 | /** |
| 30 | * @param bool $skipSmallImages whether small images should be excluded from lazy loading |
| 31 | */ |
| 32 | public function __construct( $skipSmallImages = false ) { |
| 33 | $this->skipSmall = $skipSmallImages; |
| 34 | } |
| 35 | |
| 36 | /** |
| 37 | * Insert a image placeholder into the element |
| 38 | * which will be lazy loaded via JS. |
| 39 | * Assumes Legacy parser, not compatible with Parsoid. |
| 40 | * |
| 41 | * @param DOMElement $node to be transformed |
| 42 | */ |
| 43 | public function apply( DOMElement $node ) { |
| 44 | $sections = DOMCompat::querySelectorAll( $node, 'section' ); |
| 45 | foreach ( $sections as $sectionNumber => $section ) { |
| 46 | if ( $sectionNumber > 0 ) { |
| 47 | $this->doRewriteImagesForLazyLoading( $section, $section->ownerDocument ); |
| 48 | } |
| 49 | } |
| 50 | } |
| 51 | |
| 52 | /** |
| 53 | * @see MobileFormatter#getImageDimensions |
| 54 | * |
| 55 | * @param DOMElement $img |
| 56 | * @param string $dimension Either "width" or "height" |
| 57 | * @return string|null |
| 58 | */ |
| 59 | private function getImageDimension( DOMElement $img, $dimension ) { |
| 60 | $style = $img->getAttribute( 'style' ); |
| 61 | $numMatches = preg_match( "/.*?{$dimension} *\: *([^;]*)/", $style, $matches ); |
| 62 | |
| 63 | if ( !$numMatches && !$img->hasAttribute( $dimension ) ) { |
| 64 | return null; |
| 65 | } |
| 66 | |
| 67 | return $numMatches |
| 68 | ? trim( $matches[1] ) |
| 69 | : $img->getAttribute( $dimension ) . 'px'; |
| 70 | } |
| 71 | |
| 72 | /** |
| 73 | * Determine the user perceived width and height of an image element based on `style`, `width`, |
| 74 | * and `height` attributes. |
| 75 | * |
| 76 | * As in the browser, the `style` attribute takes precedence over the `width` and `height` |
| 77 | * attributes. If the image has no `style`, `width` or `height` attributes, then the image is |
| 78 | * dimensionless. |
| 79 | * |
| 80 | * @param DOMElement $img <img> element |
| 81 | * @return array with width and height parameters if dimensions are found |
| 82 | */ |
| 83 | public function getImageDimensions( DOMElement $img ) { |
| 84 | $result = []; |
| 85 | |
| 86 | foreach ( [ 'width', 'height' ] as $dimensionName ) { |
| 87 | $dimension = $this->getImageDimension( $img, $dimensionName ); |
| 88 | |
| 89 | if ( $dimension ) { |
| 90 | $result[$dimensionName] = $dimension; |
| 91 | } |
| 92 | } |
| 93 | |
| 94 | return $result; |
| 95 | } |
| 96 | |
| 97 | /** |
| 98 | * Is image dimension small enough to not lazy load it |
| 99 | * |
| 100 | * @param string $dimension in css format, supports only px|ex units |
| 101 | * @return bool |
| 102 | */ |
| 103 | public function isDimensionSmallerThanThreshold( $dimension ) { |
| 104 | $matches = null; |
| 105 | if ( preg_match( '/(\d+)(\.\d+)?(px|ex)/', $dimension, $matches ) === 0 ) { |
| 106 | return false; |
| 107 | } |
| 108 | |
| 109 | $size = $matches[1]; |
| 110 | $unit = array_pop( $matches ); |
| 111 | |
| 112 | switch ( strtolower( $unit ) ) { |
| 113 | case 'px': |
| 114 | return $size <= self::SMALL_IMAGE_DIMENSION_THRESHOLD_IN_PX; |
| 115 | case 'ex': |
| 116 | return $size <= self::SMALL_IMAGE_DIMENSION_THRESHOLD_IN_EX; |
| 117 | default: |
| 118 | return false; |
| 119 | } |
| 120 | } |
| 121 | |
| 122 | /** |
| 123 | * @param array $dimensions |
| 124 | * @return bool |
| 125 | */ |
| 126 | private function skipLazyLoadingForSmallDimensions( array $dimensions ) { |
| 127 | if ( array_key_exists( 'width', $dimensions ) |
| 128 | && $this->isDimensionSmallerThanThreshold( $dimensions['width'] ) |
| 129 | ) { |
| 130 | return true; |
| 131 | } |
| 132 | if ( array_key_exists( 'height', $dimensions ) |
| 133 | && $this->isDimensionSmallerThanThreshold( $dimensions['height'] ) |
| 134 | ) { |
| 135 | return true; |
| 136 | } |
| 137 | return false; |
| 138 | } |
| 139 | |
| 140 | /** |
| 141 | * Enables images to be loaded asynchronously |
| 142 | * |
| 143 | * @param DOMElement|DOMDocument $el Element or document to rewrite images in. |
| 144 | * @param ?DOMDocument $doc Document to create elements in |
| 145 | */ |
| 146 | private function doRewriteImagesForLazyLoading( $el, ?DOMDocument $doc ) { |
| 147 | if ( $doc === null ) { |
| 148 | return; |
| 149 | } |
| 150 | $lazyLoadSkipSmallImages = $this->skipSmall; |
| 151 | |
| 152 | foreach ( DOMCompat::querySelectorAll( $el, 'img' ) as $img ) { |
| 153 | $parent = $img->parentNode; |
| 154 | $dimensions = $this->getImageDimensions( $img ); |
| 155 | $hasCompleteDimensions = isset( $dimensions['width'] ) && isset( $dimensions['height'] ); |
| 156 | |
| 157 | if ( $lazyLoadSkipSmallImages |
| 158 | && $this->skipLazyLoadingForSmallDimensions( $dimensions ) |
| 159 | ) { |
| 160 | continue; |
| 161 | } |
| 162 | // T133085 - don't transform if we have no idea about dimensions of image |
| 163 | if ( !$hasCompleteDimensions ) { |
| 164 | continue; |
| 165 | } |
| 166 | |
| 167 | // HTML only clients |
| 168 | $noscript = $doc->createElement( 'noscript' ); |
| 169 | |
| 170 | // To be loaded image placeholder |
| 171 | $imgPlaceholder = $doc->createElement( 'span' ); |
| 172 | $this->copyClasses( |
| 173 | $img, |
| 174 | $imgPlaceholder, |
| 175 | [ |
| 176 | // T199351 |
| 177 | 'thumbborder' |
| 178 | ], |
| 179 | [ |
| 180 | 'lazy-image-placeholder', |
| 181 | ] |
| 182 | ); |
| 183 | |
| 184 | $this->copyStyles( |
| 185 | $img, |
| 186 | $imgPlaceholder, |
| 187 | [ |
| 188 | // T207929 |
| 189 | 'vertical-align' |
| 190 | ], |
| 191 | [ |
| 192 | 'width' => $dimensions['width'], |
| 193 | 'height' => $dimensions['height'], |
| 194 | ] |
| 195 | ); |
| 196 | foreach ( [ 'src', 'alt', 'width', 'height', 'srcset', 'class', 'usemap' ] as $attr ) { |
| 197 | if ( $img->hasAttribute( $attr ) ) { |
| 198 | $imgPlaceholder->setAttribute( "data-$attr", $img->getAttribute( $attr ) ); |
| 199 | } |
| 200 | } |
| 201 | // Assume data saving and remove srcset attribute from the non-js experience |
| 202 | $img->removeAttribute( 'srcset' ); |
| 203 | |
| 204 | // T145222: Add a non-breaking space inside placeholders to ensure that they do not report |
| 205 | // themselves as invisible when inline. |
| 206 | $imgPlaceholder->appendChild( $doc->createEntityReference( 'nbsp' ) ); |
| 207 | |
| 208 | // Set the placeholder where the original image was |
| 209 | $parent->replaceChild( $imgPlaceholder, $img ); |
| 210 | // Add the original image to the HTML only markup |
| 211 | $noscript->appendChild( $img ); |
| 212 | // Insert the HTML only markup before the placeholder |
| 213 | $parent->insertBefore( $noscript, $imgPlaceholder ); |
| 214 | } |
| 215 | } |
| 216 | |
| 217 | /** |
| 218 | * Copy allowed styles from one HTMLElement to another, filtering them and |
| 219 | * unconditionally adding several in front of list |
| 220 | * |
| 221 | * @param DOMElement|DOMDocument $from html element styles to be copied from |
| 222 | * @param DOMElement|DOMDocument $to html element styles to be copied to |
| 223 | * @param string[] $enabled list of enabled styles to be copied |
| 224 | * @param array $additional key-value array of styles to be added/overriden unconditionally |
| 225 | * at the beginning of string |
| 226 | * |
| 227 | */ |
| 228 | private function copyStyles( $from, $to, array $enabled, array $additional ) { |
| 229 | $styles = HtmlStyleUtils::parseStyleString( |
| 230 | $from->hasAttribute( 'style' ) ? $from->getAttribute( 'style' ) : '' |
| 231 | ); |
| 232 | |
| 233 | $filteredStyles = HtmlStyleUtils::filterAllowedStyles( $styles, $enabled, $additional ); |
| 234 | $to->setAttribute( 'style', HtmlStyleUtils::formStyleString( $filteredStyles ) ); |
| 235 | } |
| 236 | |
| 237 | /** |
| 238 | * Copy allowed classes from one HTMLElement to another |
| 239 | * @param DOMElement|DOMDocument $from html element classes to be copied from |
| 240 | * @param DOMElement|DOMDocument $to html element classes to be copied to |
| 241 | * @param string[] $enabled array of enabled classes to be copied |
| 242 | * @param string[] $additional array of classes to be added/overriden unconditionally |
| 243 | * to the beginning |
| 244 | */ |
| 245 | private function copyClasses( $from, $to, array $enabled, array $additional ) { |
| 246 | $styles = HtmlClassUtils::parseClassString( |
| 247 | $from->hasAttribute( 'class' ) ? $from->getAttribute( 'class' ) : '' |
| 248 | ); |
| 249 | |
| 250 | $filteredClasses = HtmlClassUtils::filterAllowedClasses( $styles, $enabled, $additional ); |
| 251 | $to->setAttribute( 'class', HtmlClassUtils::formClassString( $filteredClasses ) ); |
| 252 | } |
| 253 | |
| 254 | /** |
| 255 | * Fallback for Grade C to load lazy-load image placeholders. |
| 256 | * |
| 257 | * Note: This will add a single repaint for Grade C browsers as |
| 258 | * images enter view but this is intentional and deemed acceptable. |
| 259 | * |
| 260 | * @return string The JavaScript code to load lazy placeholders in Grade C browsers |
| 261 | */ |
| 262 | public static function gradeCImageSupport() { |
| 263 | // Notes: |
| 264 | // * Document#getElementsByClassName is supported by IE9+ and #querySelectorAll is |
| 265 | // supported by IE8+. To gain the widest possible browser support we scan for |
| 266 | // noscript tags using #getElementsByTagName and look at the next sibling. |
| 267 | // If the next sibling has the lazy-image-placeholder class then it will be assumed |
| 268 | // to be a placeholder and replace with an img tag. |
| 269 | // * Iterating over the live NodeList from getElementsByTagName() is suboptimal |
| 270 | // but in IE < 9, Array#slice() throws when given a NodeList. It also requires |
| 271 | // the 2nd argument ('end'). |
| 272 | $js = <<<JAVASCRIPT |
| 273 | (window.NORLQ = window.NORLQ || []).push( function () { |
| 274 | var ns, i, p, img; |
| 275 | ns = document.getElementsByTagName( 'noscript' ); |
| 276 | for ( i = 0; i < ns.length; i++ ) { |
| 277 | p = ns[i].nextSibling; |
| 278 | if ( p && p.className && p.className.indexOf( 'lazy-image-placeholder' ) > -1 ) { |
| 279 | img = document.createElement( 'img' ); |
| 280 | img.setAttribute( 'src', p.getAttribute( 'data-src' ) ); |
| 281 | img.setAttribute( 'width', p.getAttribute( 'data-width' ) ); |
| 282 | img.setAttribute( 'height', p.getAttribute( 'data-height' ) ); |
| 283 | img.setAttribute( 'alt', p.getAttribute( 'data-alt' ) ); |
| 284 | p.parentNode.replaceChild( img, p ); |
| 285 | } |
| 286 | } |
| 287 | } ); |
| 288 | JAVASCRIPT; |
| 289 | return $js; |
| 290 | } |
| 291 | } |