Editor: Add font size constraints for fluid typography.

This commit:
* Adds default minimum font size limits so that min font size, where provided, does not become smaller than `14px`/`0.875rem`/`0.875em`.
* For font sizes of `< 14px` that have no defined minimum sizes, uses the font size to set the floor of the `clamp()` value.

This bugfix prevents converting existing small font sizes to clamp values that will reduce their font size even further in narrow widths. It therefore improves backward compatibility and accessibility.

Original PR from Gutenberg repository:
* [WordPress/gutenberg#44993 #44993 Fluid typography: add font size constraints]

Follow-up to [54260], [54360], [54497], [54500].

Props ramonopoly, andrewserong, isabel_brison, Joen, bernhard-reiter.
See #56467.
Built from https://develop.svn.wordpress.org/trunk@54646


git-svn-id: https://core.svn.wordpress.org/trunk@54198 1a063a9b-81f0-0310-95a4-ce76da25c4cd

Author: SergeyBiryukov

wp-includes/block-supports/typography.php

@@ -119,11 +119,11 @@ function wp_apply_typography_support( $block_type, $block_attributes ) {
 		$custom_font_size                    = isset( $block_attributes['style']['typography']['fontSize'] )
 			? $block_attributes['style']['typography']['fontSize']
 			: null;
-			$typography_block_styles['fontSize'] = $preset_font_size ? $preset_font_size : wp_get_typography_font_size_value(
-				array(
-					'size' => $custom_font_size,
-				)
-			);
+		$typography_block_styles['fontSize'] = $preset_font_size ? $preset_font_size : wp_get_typography_font_size_value(
+			array(
+				'size' => $custom_font_size,
+			)
+		);
 	}
 
 	if ( $has_font_family_support && ! $should_skip_font_family ) {
@@ -348,8 +348,17 @@ function wp_get_typography_value_and_unit( $raw_value, $options = array() ) {
 		$unit  = $options['coerce_to'];
 	}
 
+	/*
+	 * No calculation is required if swapping between em and rem yet,
+	 * since we assume a root size value. Later we might like to differentiate between
+	 * :root font size (rem) and parent element font size (em) relativity.
+	 */
+	if ( ( 'em' === $options['coerce_to'] || 'rem' === $options['coerce_to'] ) && ( 'em' === $unit || 'rem' === $unit ) ) {
+		$unit = $options['coerce_to'];
+	}
+
 	return array(
-		'value' => $value,
+		'value' => round( $value, 3 ),
 		'unit'  => $unit,
 	);
 }
@@ -380,26 +389,29 @@ function wp_get_computed_fluid_typography_value( $args = array() ) {
 	$minimum_font_size_raw      = isset( $args['minimum_font_size'] ) ? $args['minimum_font_size'] : null;
 	$scale_factor               = isset( $args['scale_factor'] ) ? $args['scale_factor'] : null;
 
-	// Grab the minimum font size and normalize it in order to use the value for calculations.
+	// Normalizes the minimum font size in order to use the value for calculations.
 	$minimum_font_size = wp_get_typography_value_and_unit( $minimum_font_size_raw );
 
-	// We get a 'preferred' unit to keep units consistent when calculating, otherwise the result will not be accurate.
+	/*
+	 * We get a 'preferred' unit to keep units consistent when calculating,
+	 * otherwise the result will not be accurate.
+	 */
 	$font_size_unit = isset( $minimum_font_size['unit'] ) ? $minimum_font_size['unit'] : 'rem';
 
-	// Grab the maximum font size and normalize it in order to use the value for calculations.
+	// Normalizes the maximum font size in order to use the value for calculations.
 	$maximum_font_size = wp_get_typography_value_and_unit(
 		$maximum_font_size_raw,
 		array(
 			'coerce_to' => $font_size_unit,
 		)
 	);
 
-	// Protect against unsupported units.
+	// Checks for mandatory min and max sizes, and protects against unsupported units.
 	if ( ! $maximum_font_size || ! $minimum_font_size ) {
 		return null;
 	}
 
-	// Use rem for accessible fluid target font scaling.
+	// Uses rem for accessible fluid target font scaling.
 	$minimum_font_size_rem = wp_get_typography_value_and_unit(
 		$minimum_font_size_raw,
 		array(
@@ -427,8 +439,9 @@ function wp_get_computed_fluid_typography_value( $args = array() ) {
 	 */
 	$view_port_width_offset = round( $minimum_viewport_width['value'] / 100, 3 ) . $font_size_unit;
 	$linear_factor          = 100 * ( ( $maximum_font_size['value'] - $minimum_font_size['value'] ) / ( $maximum_viewport_width['value'] - $minimum_viewport_width['value'] ) );
-	$linear_factor          = round( $linear_factor, 3 ) * $scale_factor;
-	$fluid_target_font_size = implode( '', $minimum_font_size_rem ) . " + ((1vw - $view_port_width_offset) * $linear_factor)";
+	$linear_factor_scaled   = round( $linear_factor * $scale_factor, 3 );
+	$linear_factor_scaled   = empty( $linear_factor_scaled ) ? 1 : $linear_factor_scaled;
+	$fluid_target_font_size = implode( '', $minimum_font_size_rem ) . " + ((1vw - $view_port_width_offset) * $linear_factor_scaled)";
 
 	return "clamp($minimum_font_size_raw, $fluid_target_font_size, $maximum_font_size_raw)";
 }
@@ -478,6 +491,7 @@ function wp_get_typography_font_size_value( $preset, $should_use_fluid_typograph
 	$default_minimum_font_size_factor = 0.75;
 	$default_maximum_font_size_factor = 1.5;
 	$default_scale_factor             = 1;
+	$default_minimum_font_size_limit  = '14px';
 
 	// Font sizes.
 	$fluid_font_size_settings = isset( $preset['fluid'] ) ? $preset['fluid'] : null;
@@ -499,13 +513,48 @@ function wp_get_typography_font_size_value( $preset, $should_use_fluid_typograph
 		return $preset['size'];
 	}
 
-	// If no fluid min or max font sizes are available, create some using min/max font size factors.
+	// If no fluid max font size is available, create one using max font size factor.
+	if ( ! $maximum_font_size_raw ) {
+		$maximum_font_size_raw = round( $preferred_size['value'] * $default_maximum_font_size_factor, 3 ) . $preferred_size['unit'];
+	}
+
+	// If no fluid min font size is available, create one using min font size factor.
 	if ( ! $minimum_font_size_raw ) {
-		$minimum_font_size_raw = ( $preferred_size['value'] * $default_minimum_font_size_factor ) . $preferred_size['unit'];
+		$minimum_font_size_raw = round( $preferred_size['value'] * $default_minimum_font_size_factor, 3 ) . $preferred_size['unit'];
 	}
 
-	if ( ! $maximum_font_size_raw ) {
-		$maximum_font_size_raw = ( $preferred_size['value'] * $default_maximum_font_size_factor ) . $preferred_size['unit'];
+	// Normalizes the minimum font size limit according to the incoming unit, so we can perform checks using it.
+	$minimum_font_size_limit = wp_get_typography_value_and_unit(
+		$default_minimum_font_size_limit,
+		array(
+			'coerce_to' => $preferred_size['unit'],
+		)
+	);
+
+	if ( ! empty( $minimum_font_size_limit ) ) {
+		/*
+		 * If a minimum size was not passed to this function
+		 * and the user-defined font size is lower than $minimum_font_size_limit,
+		 * then use the user-defined font size as the minimum font-size.
+		 */
+		if ( ! isset( $fluid_font_size_settings['min'] ) && $preferred_size['value'] < $minimum_font_size_limit['value'] ) {
+			$minimum_font_size_raw = implode( '', $preferred_size );
+		} else {
+			$minimum_font_size_parsed = wp_get_typography_value_and_unit(
+				$minimum_font_size_raw,
+				array(
+					'coerce_to' => $preferred_size['unit'],
+				)
+			);
+
+			/*
+			 * If the passed or calculated minimum font size is lower than $minimum_font_size_limit
+			 * use $minimum_font_size_limit instead.
+			 */
+			if ( ! empty( $minimum_font_size_parsed ) && $minimum_font_size_parsed['value'] < $minimum_font_size_limit['value'] ) {
+				$minimum_font_size_raw = implode( '', $minimum_font_size_limit );
+			}
+		}
 	}
 
 	$fluid_font_size_value = wp_get_computed_fluid_typography_value(

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.2-alpha-54645';
+$wp_version = '6.2-alpha-54646';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.