Backport background image block support from Gutenberg

src/wp-includes/block-supports/background.php

@@ -0,0 +1,112 @@
+<?php
+/**
+ * Background block support flag.
+ *
+ * @package WordPress
+ * @since 6.4.0
+ */
+
+/**
+ * Registers the style block attribute for block types that support it.
+ *
+ * @since 6.4.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type Block Type.
+ */
+function wp_register_background_support( $block_type ) {
+	// Setup attributes and styles within that if needed.
+	if ( ! $block_type->attributes ) {
+		$block_type->attributes = array();
+	}
+
+	// Check for existing style attribute definition e.g. from block.json.
+	if ( array_key_exists( 'style', $block_type->attributes ) ) {
+		return;
+	}
+
+	$has_background_support = block_has_support( $block_type, array( 'background' ), false );
+
+	if ( $has_background_support ) {
+		$block_type->attributes['style'] = array(
+			'type' => 'object',
+		);
+	}
+}
+
+/**
+ * Renders the background styles to the block wrapper.
+ * This block support uses the `render_block` hook to ensure that
+ * it is also applied to non-server-rendered blocks.
+ *
+ * @since 6.4.0
+ * @access private
+ *
+ * @param  string $block_content Rendered block content.
+ * @param  array  $block         Block object.
+ * @return string Filtered block content.
+ */
+function wp_render_background_support( $block_content, $block ) {
+	$block_type                   = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
+	$block_attributes             = $block['attrs'];
+	$has_background_image_support = block_has_support( $block_type, array( 'background', 'backgroundImage' ), false );
+
+	if (
+		! $has_background_image_support ||
+		wp_should_skip_block_supports_serialization( $block_type, 'background', 'backgroundImage' )
+	) {
+		return $block_content;
+	}
+
+	$background_image_source = _wp_array_get( $block_attributes, array( 'style', 'background', 'backgroundImage', 'source' ), null );
+	$background_image_url    = _wp_array_get( $block_attributes, array( 'style', 'background', 'backgroundImage', 'url' ), null );
+	$background_size         = _wp_array_get( $block_attributes, array( 'style', 'background', 'backgroundSize' ), 'cover' );
+
+	$background_block_styles = array();
+
+	if (
+		'file' === $background_image_source &&
+		$background_image_url
+	) {
+		// Set file based background URL.
+		$background_block_styles['backgroundImage']['url'] = $background_image_url;
+		// Only output the background size when an image url is set.
+		$background_block_styles['backgroundSize'] = $background_size;
+	}
+
+	$styles = wp_style_engine_get_styles( array( 'background' => $background_block_styles ) );
+
+	if ( ! empty( $styles['css'] ) ) {
+		// Inject background styles to the first element, presuming it's the wrapper, if it exists.
+		$tags = new WP_HTML_Tag_Processor( $block_content );
+
+		if ( $tags->next_tag() ) {
+			$existing_style = $tags->get_attribute( 'style' );
+			$updated_style  = '';
+
+			if ( ! empty( $existing_style ) ) {
+				$updated_style = $existing_style;
+				if ( ! str_ends_with( $existing_style, ';' ) ) {
+					$updated_style .= ';';
+				}
+			}
+
+			$updated_style .= $styles['css'];
+			$tags->set_attribute( 'style', $updated_style );
+		}
+
+		return $tags->get_updated_html();
+	}
+
+	return $block_content;
+}
+
+// Register the block support.
+WP_Block_Supports::get_instance()->register(
+	'background',
+	array(
+		'register_attribute' => 'wp_register_background_support',
+	)
+);
+
+add_filter( 'render_block', 'wp_render_background_support', 10, 2 );

src/wp-includes/class-wp-theme-json.php

@@ -342,13 +342,16 @@ class WP_Theme_JSON {
 	 * @since 6.2.0 Added `dimensions.minHeight`, 'shadow.presets', 'shadow.defaultPresets',
 	 *              `position.fixed` and `position.sticky`.
 	 * @since 6.3.0 Added support for `typography.textColumns`, removed `layout.definitions`.
-	 * @since 6.4.0 Added `layout.allowEditing` and `typography.writingMode`.
-	 *
+	 * @since 6.4.0 Added support for `layout.allowEditing`, `background.backgroundImage`,
+	 *              and `typography.writingMode`.
 	 * @var array
 	 */
 	const VALID_SETTINGS = array(
 		'appearanceTools'               => null,
 		'useRootPaddingAwareAlignments' => null,
+		'background'                    => array(
+			'backgroundImage' => null,
+		),
 		'border'                        => array(
 			'color'  => null,
 			'radius' => null,
@@ -563,9 +566,11 @@ public static function get_element_class_name( $element ) {
 	 *
 	 * @since 6.0.0
 	 * @since 6.2.0 Added `dimensions.minHeight` and `position.sticky`.
+	 * @since 6.4.0 Added `background.backgroundImage`.
 	 * @var array
 	 */
 	const APPEARANCE_TOOLS_OPT_INS = array(
+		array( 'background', 'backgroundImage' ),
 		array( 'border', 'color' ),
 		array( 'border', 'radius' ),
 		array( 'border', 'style' ),

src/wp-includes/style-engine/class-wp-style-engine.php

@@ -22,6 +22,7 @@
  * @access private
  * @since 6.1.0
  * @since 6.3.0 Added support for text-columns.
+ * @since 6.4.0 Added support for background.backgroundImage.
  */
 #[AllowDynamicProperties]
 final class WP_Style_Engine {
@@ -51,6 +52,21 @@ final class WP_Style_Engine {
 	 * @var array
 	 */
 	const BLOCK_STYLE_DEFINITIONS_METADATA = array(
+		'background' => array(
+			'backgroundImage' => array(
+				'property_keys' => array(
+					'default' => 'background-image',
+				),
+				'value_func'    => array( self::class, 'get_url_or_value_css_declaration' ),
+				'path'          => array( 'background', 'backgroundImage' ),
+			),
+			'backgroundSize'  => array(
+				'property_keys' => array(
+					'default' => 'background-size',
+				),
+				'path'          => array( 'background', 'backgroundSize' ),
+			),
+		),
 		'color'      => array(
 			'text'       => array(
 				'property_keys' => array(
@@ -589,6 +605,42 @@ protected static function get_individual_property_css_declarations( $style_value
 		return $css_declarations;
 	}
 
+	/**
+	 * Style value parser that constructs a CSS definition array comprising a single CSS property and value.
+	 * If the provided value is an array containing a `url` property, the function will return a CSS definition array
+	 * with a single property and value, with `url` escaped and injected into a CSS `url()` function,
+	 * e.g., array( 'background-image' => "url( '...' )" ).
+	 *
+	 * @since 6.4.0
+	 *
+	 * @param array $style_value      A single raw style value from $block_styles array.
+	 * @param array $style_definition A single style definition from BLOCK_STYLE_DEFINITIONS_METADATA.
+	 * @return string[] An associative array of CSS definitions, e.g., array( "$property" => "$value", "$property" => "$value" ).
+	 */
+	protected static function get_url_or_value_css_declaration( $style_value, $style_definition ) {
+		if ( empty( $style_value ) ) {
+			return array();
+		}
+
+		$css_declarations = array();
+
+		if ( isset( $style_definition['property_keys']['default'] ) ) {
+			$value = null;
+
+			if ( ! empty( $style_value['url'] ) ) {
+				$value = "url('" . $style_value['url'] . "')";
+			} elseif ( is_string( $style_value ) ) {
+				$value = $style_value;
+			}
+
+			if ( null !== $value ) {
+				$css_declarations[ $style_definition['property_keys']['default'] ] = $value;
+			}
+		}
+
+		return $css_declarations;
+	}
+
 	/**
 	 * Returns compiled CSS from CSS declarations.
 	 *

src/wp-settings.php

@@ -340,6 +340,7 @@
 require ABSPATH . WPINC . '/class-wp-block-supports.php';
 require ABSPATH . WPINC . '/block-supports/utils.php';
 require ABSPATH . WPINC . '/block-supports/align.php';
+require ABSPATH . WPINC . '/block-supports/background.php';
 require ABSPATH . WPINC . '/block-supports/border.php';
 require ABSPATH . WPINC . '/block-supports/colors.php';
 require ABSPATH . WPINC . '/block-supports/custom-classname.php';