Allow developers to select which image format to use for images in the content

modules/images/webp-uploads/load.php

@@ -599,11 +599,34 @@ function webp_uploads_img_tag_update_mime_type( $image, $context, $attachment_id
 		return $image;
 	}
 
-	$urls = $matches[0];
-	// TODO: Add a filterable option to change the selected mime type. See https://github.com/WordPress/performance/issues/187.
-	$target_mime = 'image/webp';
+	/**
+	 * Filters mime types that should be used to update all images in the content. The order of
+	 * mime types matters. The last mime type in the list will be used if it is supported by an image.
+	 *
+	 * @since n.e.x.t
+	 *
+	 * @param array  $target_mimes  The list of mime types that can be used to update images in the content.
+	 * @param int    $attachment_id The attachment ID.
+	 * @param string $context       The current context.
+	 */
+	$target_mimes = apply_filters( 'webp_uploads_content_image_mimes', array( 'image/jpeg', 'image/webp' ), $attachment_id, $context );
+
+	$target_mime = null;
+	// Look for the most progressive image format first.
+	$target_mimes = array_reverse( $target_mimes );
+	foreach ( $target_mimes as $mime ) {
+		if ( isset( $metadata['sources'][ $mime ] ) ) {
+			$target_mime = $mime;
+			break;
+		}
+	}
+
+	if ( null === $target_mime ) {
+		return $image;
+	}
 
 	$basename = wp_basename( $metadata['file'] );
+	$urls     = $matches[0];
 	foreach ( $urls as $url ) {
 		$src_filename = wp_basename( $url );
 

tests/modules/images/webp-uploads/webp-uploads-test.php

@@ -513,6 +513,31 @@ public function it_should_replace_the_references_to_a_jpg_image_to_a_webp_versio
 		$this->assertSame( $expected_tag, webp_uploads_img_tag_update_mime_type( $tag, 'the_content', $attachment_id ) );
 	}
 
+	/**
+	 * Should not replace jpeg images in the content if other mime types are disabled via filter.
+	 *
+	 * @dataProvider provider_replace_images_with_different_extensions
+	 * @group webp_uploads_update_image_references
+	 *
+	 * @test
+	 */
+	public function it_should_not_replace_the_references_to_a_jpg_image_when_disabled_via_filter( $image_path ) {
+		remove_all_filters( 'webp_uploads_content_image_mimes' );
+
+		add_filter(
+			'webp_uploads_content_image_mimes',
+			function( $mime_types ) {
+				unset( $mime_types[ array_search( 'image/webp', $mime_types, true ) ] );
+				return $mime_types;
+			}
+		);
+
+		$attachment_id = $this->factory->attachment->create_upload_object( $image_path );
+		$tag           = wp_get_attachment_image( $attachment_id, 'medium', false, array( 'class' => "wp-image-{$attachment_id}" ) );
+
+		$this->assertSame( $tag, webp_uploads_img_tag_update_mime_type( $tag, 'the_content', $attachment_id ) );
+	}
+
 	public function provider_replace_images_with_different_extensions() {
 		yield 'An image with a .jpg extension' => array( TESTS_PLUGIN_DIR . '/tests/testdata/modules/images/leafs.jpg' );
 		yield 'An image with a .jpeg extension' => array( TESTS_PLUGIN_DIR . '/tests/testdata/modules/images/car.jpeg' );