Ticket #34528: 34528.3.diff

src/wp-includes/media.php

@@ -983 +983 @@
                 return false;
         }
 
-        // Don't add srcset attributes to (animated) gifs that are inserted at full size.
-        if ( isset( $image_sizes['thumbnail']['mime-type'] ) && 'image/gif' === $image_sizes['thumbnail']['mime-type'] &&
-                false !== strpos( $image_src, $image_meta['file'] ) ) {
-
-                return false;
-        }
-
         $image_basename = wp_basename( $image_meta['file'] );
         $image_baseurl = _wp_upload_dir_baseurl();
 
-        // Add full size to the '$image_sizes' array.
-        $image_sizes['full'] = array(
-                'width'  => $image_meta['width'],
-                'height' => $image_meta['height'],
-                'file'   => $image_basename,
-        );
+        /*
+         * WordPress flattens animated GIFs into one frame when generating intermediate sizes.
+         * To avoid hiding animation in user content, if src is a full size GIF, a srcset attribute is not generated.
+         * If src is an intermediate size GIF, the full size is excluded from srcset to keep a flattened GIF from becoming animated.
+         */
+        if ( isset( $image_sizes['thumbnail']['mime-type'] ) && 'image/gif' === $image_sizes['thumbnail']['mime-type'] ) {
+                if ( strpos( $image_src, $image_meta['file'] ) ) {
+                        return false;
+                }
+        } else {
+                $image_sizes['full'] = array(
+                        'width'  => $image_meta['width'],
+                        'height' => $image_meta['height'],
+                        'file'   => $image_basename,
+                );
+        }
 
         // Uploads are (or have been) in year/month sub-directories.
         if ( $image_basename !== $image_meta['file'] ) {

tests/phpunit/tests/media.php

@@ -996 +996 @@
                         )
                 );
 
-                $image_src = 'http://' . WP_TESTS_DOMAIN . '/wp-content/uploads/' . $image_meta['file'];
+                $full_src  = 'http://' . WP_TESTS_DOMAIN . '/wp-content/uploads/' . $image_meta['file'];
+                $large_src = 'http://' . WP_TESTS_DOMAIN . '/wp-content/uploads/' . $image_meta['sizes']['large']['file'];
+
                 // Test with soft resized size array.
                 $size_array = array(900, 450);
 
-                $this->assertFalse( wp_calculate_image_srcset( $image_src, $size_array, $image_meta ) );
+                // Full size GIFs should not return a srcset.
+                $this->assertFalse( wp_calculate_image_srcset( $full_src, $size_array, $image_meta ) );
+                // Intermediate sized GIFs should not include the full size in the srcset.
+                $this->assertFalse( strpos( wp_calculate_image_srcset( $large_src, $size_array, $image_meta ), $full_src ) );
         }
 }