+ /**
+ * @param ResourceLoaderContext $context
+ * @return array
+ */
+ public function getPreloadLinks( ResourceLoaderContext $context ) {
+ return $this->getLogoPreloadlinks();
+ }
+
+ /**
+ * Helper method for getPreloadLinks()
+ * @return array
+ */
+ private function getLogoPreloadlinks() {
+ $logo = $this->getLogoData( $this->getConfig() );
+
+ $tags = [];
+ $logosPerDppx = [];
+ $logos = [];
+
+ $preloadLinks = [];
+
+ if ( !is_array( $logo ) ) {
+ // No media queries required if we only have one variant
+ $preloadLinks[ $logo ] = [ 'as' => 'image' ];
+ return $preloadLinks;
+ }
+
+ if ( isset( $logo['svg'] ) ) {
+ // No media queries required if we only have a 1x and svg variant
+ // because all preload-capable browsers support SVGs
+ $preloadLinks [ $logo['svg'] ] = [ 'as' => 'image' ];
+ return $preloadLinks;
+ }
+
+ foreach ( $logo as $dppx => $src ) {
+ // Keys are in this format: "1.5x"
+ $dppx = substr( $dppx, 0, -1 );
+ $logosPerDppx[$dppx] = $src;
+ }
+
+ // Because PHP can't have floats as array keys
+ uksort( $logosPerDppx, function ( $a , $b ) {
+ $a = floatval( $a );
+ $b = floatval( $b );
+ // Sort from smallest to largest (e.g. 1x, 1.5x, 2x)
+ return $a <=> $b;
+ } );
+
+ foreach ( $logosPerDppx as $dppx => $src ) {
+ $logos[] = [ 'dppx' => $dppx, 'src' => $src ];
+ }
+
+ $logosCount = count( $logos );
+ // Logic must match ResourceLoaderSkinModule:
+ // - 1x applies to resolution < 1.5dppx
+ // - 1.5x applies to resolution >= 1.5dppx && < 2dppx
+ // - 2x applies to resolution >= 2dppx
+ // Note that min-resolution and max-resolution are both inclusive.
+ for ( $i = 0; $i < $logosCount; $i++ ) {
+ if ( $i === 0 ) {
+ // Smallest dppx
+ // min-resolution is ">=" (larger than or equal to)
+ // "not min-resolution" is essentially "<"
+ $media_query = 'not all and (min-resolution: ' . $logos[ 1 ]['dppx'] . 'dppx)';
+ } elseif ( $i !== $logosCount - 1 ) {
+ // In between
+ // Media query expressions can only apply "not" to the entire expression
+ // (e.g. can't express ">= 1.5 and not >= 2).
+ // Workaround: Use <= 1.9999 in place of < 2.
+ $upper_bound = floatval( $logos[ $i + 1 ]['dppx'] ) - 0.000001;
+ $media_query = '(min-resolution: ' . $logos[ $i ]['dppx'] .
+ 'dppx) and (max-resolution: ' . $upper_bound . 'dppx)';
+ } else {
+ // Largest dppx
+ $media_query = '(min-resolution: ' . $logos[ $i ]['dppx'] . 'dppx)';
+ }
+
+ $preloadLinks[ $logos[$i]['src'] ] = [ 'as' => 'image', 'media' => $media_query ];
+ }
+
+ return $preloadLinks;
+ }
+