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<?php |
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/** |
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* Metric-matched fallback fonts (zero-CLS). |
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* |
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* For every hosted family with extracted metrics, generates a fallback |
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* @font-face that aliases a local system font but overrides its metrics |
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* (size-adjust, ascent/descent/line-gap-override) so it occupies the same space |
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* as the web font — eliminating layout shift during swap. |
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* |
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* @package EasyFonts |
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*/ |
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|
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namespace EasyFonts\Frontend; |
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|
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use EasyFonts\Fonts\Registry; |
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use EasyFonts\Parser\FontMetricsReader; |
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|
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defined( 'ABSPATH' ) || exit; |
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|
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/** |
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* Builds + injects metric-matched fallback faces. |
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*/ |
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class MetricFallbacks { |
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|
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/** |
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* @var Registry |
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*/ |
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private Registry $registry; |
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|
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/** |
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* Constructor. |
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*/ |
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public function __construct() { |
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$this->registry = new Registry(); |
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} |
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|
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/** |
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* Build the fallback stylesheet for all families touched this request. |
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* |
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* @param array<int,array{family:string,weight:string,style:string}> $touched Touched fonts. |
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* @return string CSS (may be empty). |
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*/ |
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public function build_for( array $touched ): string { |
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$seen = array(); |
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$css = ''; |
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|
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foreach ( $touched as $item ) { |
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$family = $item['family']; |
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$key = strtolower( $family ); |
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|
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if ( isset( $seen[ $key ] ) ) { |
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continue; |
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} |
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|
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$seen[ $key ] = true; |
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|
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$metrics = $this->registry->metrics_for( $family ); |
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|
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if ( ! $metrics ) { |
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continue; |
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} |
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|
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$face = $this->build_face( $family, $metrics ); |
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|
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if ( '' !== $face ) { |
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$css .= $face; |
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} |
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} |
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|
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return $css; |
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} |
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|
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/** |
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* Compute the override values and emit a fallback @font-face + nothing else. |
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* The fallback family is named "<Family> Fallback"; we also append it to the |
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* original family via a small @font-face alias is not possible, so callers |
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* should rely on the generated stack. Here we emit the override face only. |
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* |
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* @param string $family Family. |
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* @param array<string,float|int> $metrics Web-font metrics. |
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* @return string |
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*/ |
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private function build_face( string $family, array $metrics ): string { |
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$units = (float) ( $metrics['unitsPerEm'] ?? 0 ); |
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|
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if ( $units <= 0 ) { |
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return ''; |
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} |
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|
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$ascent = (float) ( $metrics['ascent'] ?? 0 ); |
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$descent = (float) ( $metrics['descent'] ?? 0 ); |
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$gap = (float) ( $metrics['lineGap'] ?? 0 ); |
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$x_avg = (float) ( $metrics['xAvgCharWidth'] ?? 0 ); |
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|
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$category = $this->guess_category( $family ); |
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$fallback = FontMetricsReader::system_fallbacks()[ $category ]; |
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|
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// size-adjust = webfont avg-width ratio / fallback avg-width ratio. |
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$web_ratio = $x_avg > 0 ? ( $x_avg / $units ) : 0; |
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$size_adj = ( $web_ratio > 0 && $fallback['ratio'] > 0 ) ? ( $web_ratio / $fallback['ratio'] ) : 1.0; |
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|
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if ( $size_adj <= 0 ) { |
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$size_adj = 1.0; |
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} |
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|
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// Overrides are relative to the web font, scaled by size-adjust. |
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$ascent_pct = ( $ascent / ( $units * $size_adj ) ) * 100; |
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$descent_pct = ( abs( $descent ) / ( $units * $size_adj ) ) * 100; |
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$gap_pct = ( $gap / ( $units * $size_adj ) ) * 100; |
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|
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// Harden against CSS-context injection: a malicious @font-face family |
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// name elsewhere on the site must not be able to break out of the |
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// declaration. Strip quotes/braces/semicolons before interpolation. |
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$family_css = self::css_safe( $family ); |
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$fallback_css = self::css_safe( (string) $fallback['local'] ); |
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|
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return sprintf( |
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"@font-face{font-family:'%s Fallback';src:local('%s');size-adjust:%s%%;ascent-override:%s%%;descent-override:%s%%;line-gap-override:%s%%;}\n", |
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$family_css, |
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$fallback_css, |
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$this->fmt( $size_adj * 100 ), |
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$this->fmt( $ascent_pct ), |
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$this->fmt( $descent_pct ), |
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$this->fmt( $gap_pct ) |
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); |
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} |
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|
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/** |
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* Strip characters that could break out of a CSS string/declaration. |
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* |
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* @param string $text Raw text. |
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* @return string |
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*/ |
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private static function css_safe( string $text ): string { |
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return trim( str_replace( array( "'", '"', ';', '{', '}', '<', '>', "\\", "\r", "\n" ), '', $text ) ); |
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} |
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|
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/** |
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* Naive serif/sans/mono category guess from the family name. |
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* |
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* @param string $family Family. |
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* @return string |
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*/ |
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private function guess_category( string $family ): string { |
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$lower = strtolower( $family ); |
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|
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if ( false !== strpos( $lower, 'mono' ) || false !== strpos( $lower, 'code' ) || false !== strpos( $lower, 'courier' ) ) { |
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return 'monospace'; |
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} |
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|
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foreach ( array( 'serif', 'slab', 'georgia', 'times', 'playfair', 'merriweather', 'lora', 'pt serif', 'noto serif' ) as $hint ) { |
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if ( false !== strpos( $lower, $hint ) ) { |
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return 'serif'; |
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} |
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} |
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|
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return 'sans-serif'; |
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} |
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|
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/** |
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* Format a percentage with up to 4 decimals, trimmed. |
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* |
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* @param float $value Value. |
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* @return string |
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*/ |
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private function fmt( float $value ): string { |
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return rtrim( rtrim( number_format( $value, 4, '.', '' ), '0' ), '.' ); |
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} |
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} |
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