From: Brian Wolff <bawolff+wn@gmail.com>
Date: Fri, 4 Jul 2014 04:46:10 +0000 (-0300)
Subject: Fix alpha transparency in XCF images
X-Git-Tag: 1.31.0-rc.0~15060^2
X-Git-Url: http://git.cyclocoop.org/%22%20.%20generer_url_ecrire%28%22suivi_revisions%22%29%20.%20%22?a=commitdiff_plain;h=9dbc0cce8a80d00d29a642cedc6e26dc7f43159a;p=lhc%2Fweb%2Fwiklou.git

Fix alpha transparency in XCF images

The -layers merge option flattens all layers on to a canvas
of whatever color -background is set to. However -background
was white for the PNG bKGD chunk. Set it to transparent just
for the -layers merge operation.

This works well on most recent image magick. Older image magick
explodes on my test image (I tested 6.6.0-4), so unclear if it
works there, but it certainly didn't make anything worse.
Wikimedia uses a version between the two that I tested so hopefully
this will make things better, and if it doesn't, it eventually will
when we update image magick.

Bug: 35622
Change-Id: I77601cdf005a64ae8ea7516cc846620431917863
---

diff --git a/includes/media/Bitmap.php b/includes/media/Bitmap.php
index 76dab03d76..bf50f2de19 100644
--- a/includes/media/Bitmap.php
+++ b/includes/media/Bitmap.php
@@ -354,7 +354,17 @@ class BitmapHandler extends ImageHandler {
 				}
 			}
 		} elseif ( $params['mimeType'] == 'image/x-xcf' ) {
-			$animation_post = array( '-layers', 'merge' );
+			// Before merging layers, we need to set the background
+			// to be transparent to preserve alpha, as -layers merge
+			// merges all layers on to a canvas filled with the
+			// background colour. After merging we reset the background
+			// to be white for the default background colour setting
+			// in the PNG image (which is used in old IE)
+			$animation_post = array(
+				'-background', 'transparent',
+				'-layers', 'merge',
+				'-background', 'white',
+			);
 			wfSuppressWarnings();
 			$xcfMeta = unserialize( $image->getMetadata() );
 			wfRestoreWarnings();