From 5aa7a8ce78b685b3aae75837f9a49b1167232155 Mon Sep 17 00:00:00 2001
From: Andrew Ozz <azaozz@git.wordpress.org>
Date: Thu, 22 Oct 2015 19:30:12 +0000
Subject: [PATCH] Responsive Images: limit the size of images included in
 `srcset` attributes. Introduce `max_srcset_image_width` filter to adjust the
 limit.

Props joemcgill.
Fixes #34341.

git-svn-id: https://develop.svn.wordpress.org/trunk@35358 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/media.php | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 210bf425c9..de1f2c480d 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -928,6 +928,15 @@ function wp_get_attachment_image_srcset_array( $attachment_id, $size = 'medium'
 	 */
 	$img_edited = preg_match( '/-e[0-9]{13}/', $img_url, $img_edit_hash );
 
+	/**
+	 * Filter the maximum width included in a srcset attribute.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @param array|string $size Size of image, either array or string.
+	 */
+	$max_srcset_width = apply_filters( 'max_srcset_image_width', 1600, $size );
+
 	/*
 	 * Set up arrays to hold url candidates and matched image sources so
 	 * we can avoid duplicates without looping through the full sources array
@@ -945,6 +954,11 @@ function wp_get_attachment_image_srcset_array( $attachment_id, $size = 'medium'
 			continue;
 		}
 
+		// Filter out images that are wider than $max_srcset_width.
+		if ( $max_srcset_width && $img['width'] > $max_srcset_width ) {
+			$contiue;
+		}
+
 		$candidate_url = path_join( dirname( $img_url ), $img['file'] );
 
 		// Calculate the new image ratio.