Copied from Debian.

From 03a820b173ed1fdef6ff14b4468f5dbc02ff59be Mon Sep 17 00:00:00 2001
From: Heiko Lewin <heiko.lewin@worldiety.de>
Date: Tue, 15 Dec 2020 16:48:19 +0100
Subject: [PATCH] Fix mask usage in image-compositor

[trimmed test case, since not used in Debian build]

---
 src/cairo-image-compositor.c                |   8 ++--

--- cairo-1.16.0.orig/src/cairo-image-compositor.c
+++ cairo-1.16.0/src/cairo-image-compositor.c
@@ -2601,14 +2601,14 @@ _inplace_src_spans (void *abstract_rende
 		    unsigned num_spans)
 {
     cairo_image_span_renderer_t *r = abstract_renderer;
-    uint8_t *m;
+    uint8_t *m, *base = (uint8_t*)pixman_image_get_data(r->mask);
     int x0;
 
     if (num_spans == 0)
 	return CAIRO_STATUS_SUCCESS;
 
     x0 = spans[0].x;
-    m = r->_buf;
+    m = base;
     do {
 	int len = spans[1].x - spans[0].x;
 	if (len >= r->u.composite.run_length && spans[0].coverage == 0xff) {
@@ -2646,7 +2646,7 @@ _inplace_src_spans (void *abstract_rende
 				      spans[0].x, y,
 				      spans[1].x - spans[0].x, h);
 
-	    m = r->_buf;
+	    m = base;
 	    x0 = spans[1].x;
 	} else if (spans[0].coverage == 0x0) {
 	    if (spans[0].x != x0) {
@@ -2675,7 +2675,7 @@ _inplace_src_spans (void *abstract_rende
 #endif
 	    }
 
-	    m = r->_buf;
+	    m = base;
 	    x0 = spans[1].x;
 	} else {
 	    *m++ = spans[0].coverage;
dc891225440ebee577f1da792c78c'>commit</a><a href='/guix/diff/tests/accounts.scm?id=f97176e78cbdc891225440ebee577f1da792c78c'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/accounts.scm'>
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<div class='path'>path: <a href='/guix/log/?id=f97176e78cbdc891225440ebee577f1da792c78c'>root</a>/<a href='/guix/log/tests?id=f97176e78cbdc891225440ebee577f1da792c78c'>tests</a>/<a href='/guix/log/tests/accounts.scm?id=f97176e78cbdc891225440ebee577f1da792c78c'>accounts.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/accounts.scm?id=f97176e78cbdc891225440ebee577f1da792c78c&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-08-28 00:27:14 +0200'>2019-08-28</span></td><td><a href='/guix/commit/tests/accounts.scm?id=dd4e46edda6c255ca170a6650c6f92b16ff50a3f'>accounts: Delete duplicate entries.</a><span class='msg-avail'>...<span class='msg-tooltip'>When adding multiple instances of a service requiring some user
account/group, we could end up with multiple entries for that account or
group in /etc/passwd or /etc/group.

* gnu/build/accounts.scm (database-writer)[write-entries]: Add call to
'delete-duplicates'.
* tests/accounts.scm ("write-passwd with duplicate entry"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-04-27 16:30:40 +0200'>2019-04-27</span></td><td><a href='/guix/commit/tests/accounts.scm?id=0c329bf4b0c00abdc9a7d9c818d36d4d60b3005d'>tests: Adjust accounts test to shell-as-config change.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 504a0fc636ec591e65b4a229a37e522e425d8a0c.

* tests/accounts.scm ("allocate-passwd with previous state"): Change
expected 'shell' for "alice" to "/bin/sh".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-25 23:37:06 +0100'>2019-03-25</span></td><td><a href='/guix/commit/tests/accounts.scm?id=cf848cc0a17a3a58d600116896f6e7abfb0440d4'>accounts: Add default value for the 'home-directory' field of &lt;user-account&gt;.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/accounts.scm (&lt;user-account&gt;)[home-directory]: Mark as
thunked and add a default value.
(default-home-directory): New procedure.
* doc/guix.texi (User Accounts): Remove 'home-directory' from example.
* gnu/system/examples/bare-bones.tmpl: Likewise.
* gnu/system/examples/beaglebone-black.tmpl: Likewise.
* gnu/system/examples/desktop.tmpl: Likewise.
* gnu/system/examples/docker-image.tmpl: Likewise.
* gnu/system/examples/lightweight-desktop.tmpl: Likewise.
* gnu/system/install.scm (installation-os): Likewise.
* gnu/tests.scm (%simple-os): Likewise.
* gnu/tests/install.scm (%minimal-os, %minimal-os-on-vda):
(%separate-home-os, %encrypted-root-os, %btrfs-root-os): Likewise.
* tests/accounts.scm ("allocate-passwd")
("allocate-passwd with previous state"): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-07 20:05:09 +0100'>2019-03-07</span></td><td><a href='/guix/commit/tests/accounts.scm?id=ec600e4544729f1aaf46fa5162bba334515d0de5'>Add (gnu build accounts).</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/accounts.scm, tests/accounts.scm: New files.
* Makefile.am (SCM_TESTS): Add tests/accounts.scm.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add build/accounts.scm.
</span></span></td><td>Ludovic Courtès</td></tr>