Add custom sizes attribute to post body images.

inc/template-functions.php

@@ -131,6 +131,36 @@ function twentynineteen_post_thumbnail_sizes_attr( $attr ) {
 }
 add_filter( 'wp_get_attachment_image_attributes', 'twentynineteen_post_thumbnail_sizes_attr', 10, 1 );
 
+/**
+ * Add custom sizes attribute to responsive image functionality for post content images.
+ *
+ * @origin Twenty Nineteen 1.0
+ *
+ * @param string       $sizes         A source size value for use in a 'sizes' attribute.
+ * @param array|string $size          Requested size. Image size or array of width and height values
+ *                                    in pixels (in that order).
+ * @param string|null  $image_src     The URL to the image file or null.
+ * @param array|null   $image_meta    The image meta data as returned by wp_get_attachment_metadata() or null.
+ * @param int          $attachment_id Image attachment ID of the original image or 0.
+ * @param array        $block_attr    Attributes from the parent block.
+ */
+function twentynineteen_calculate_image_sizes_attr( $sizes, $size, $image_src, $image_meta, $attachment_id, $block_attr ) {
+	if ( is_admin() ) {
+		return $sizes;
+	}
+
+	$align = $block_attr[align];
+	if ( '' === $align ) {
+		$sizes = '(min-width: 768px) calc(8 * (100vw / 12) - 28px), (min-width: 1168) calc(6 * 100vw/12) - 28px), calc(100% - (2 * 1rem))';
+	} elseif ( 'wide' === $align ) {
+		$sizes = '(min-width: 768px) 80%, calc(100% - (2 * 1rem))';
+	} elseif ( 'full' === $align ) {
+		$sizes = '100vw';
+	}
+	return $sizes;
+}
+add_filter( 'wp_calculate_image_sizes', 'twentynineteen_calculate_image_sizes_attr', 10, 6 );
+
 /**
  * Returns the size for avatars used in the theme.
  */

readme.txt

@@ -1,22 +1,22 @@
-=== Twenty Nineteen ===
-Contributors: the WordPress team
-Tags: one-column, flexible-header, accessibility-ready, custom-colors, custom-menu, custom-logo, editor-style, featured-images, footer-widgets, rtl-language-support, sticky-post, theme-options, threaded-comments, translation-ready
-Requires at least: 4.9.6
-Tested up to: 5.0
-Stable tag: 1.0
-License: GPLv2 or later
-License URI: http://www.gnu.org/licenses/gpl-2.0.html
-
-Our 2019 default theme is designed to show off the power of the block editor.
-
-== Description ==
-Our 2019 default theme is designed to show off the power of the block editor. It features custom styles for all the default blocks, and is built so that what you see in the editor looks like what you'll see on your website. Twenty Nineteen is designed to be adaptable to a wide range of websites, whether you’re running a photo blog, launching a new business, or supporting a non-profit. Featuring ample whitespace and modern sans-serif headlines paired with classic serif body text, it's built to be beautiful on all screen sizes.
-
-== Changelog ==
-
-= 1.0 =
-* Initial Release
-
-== Resources ==
-* normalize.css, © 2012-2018 Nicolas Gallagher and Jonathan Neal, MIT
-* Underscores, © 2012-2018 Automattic, Inc., GNU GPL v2 or later
+=== Twenty Nineteen ===
+Contributors: the WordPress team
+Tags: one-column, flexible-header, accessibility-ready, custom-colors, custom-menu, custom-logo, editor-style, featured-images, footer-widgets, rtl-language-support, sticky-post, theme-options, threaded-comments, translation-ready
+Requires at least: 4.9.6
+Tested up to: 5.0
+Stable tag: 1.0
+License: GPLv2 or later
+License URI: http://www.gnu.org/licenses/gpl-2.0.html
+
+Our 2019 default theme is designed to show off the power of the block editor.
+
+== Description ==
+Our 2019 default theme is designed to show off the power of the block editor. It features custom styles for all the default blocks, and is built so that what you see in the editor looks like what you'll see on your website. Twenty Nineteen is designed to be adaptable to a wide range of websites, whether you’re running a photo blog, launching a new business, or supporting a non-profit. Featuring ample whitespace and modern sans-serif headlines paired with classic serif body text, it's built to be beautiful on all screen sizes.
+
+== Changelog ==
+
+= 1.0 =
+* Initial Release
+
+== Resources ==
+* normalize.css, © 2012-2018 Nicolas Gallagher and Jonathan Neal, MIT
+* Underscores, © 2012-2018 Automattic, Inc., GNU GPL v2 or later