[librsvg/wip/otte: 32/39] tests: Mark pixels in diff where only the alpha channel differs

[Benjamin Otte <otte src gnome org>]

commit 5a4d161fb0f1b54de7a8e03f9ac62a6256e0ab8c
Author: Benjamin Otte <otte redhat com>
Date:   Sun Oct 18 23:59:27 2015 +0200

    tests: Mark pixels in diff where only the alpha channel differs

 tests/rsvg-test.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/tests/rsvg-test.c b/tests/rsvg-test.c
index 32062e8..6b6fe9b 100644
--- a/tests/rsvg-test.c
+++ b/tests/rsvg-test.c
@@ -103,6 +103,11 @@ buffer_diff_core (unsigned char *_buf_a,
                }
 
                result.pixels_changed++;
+               if ((diff_pixel & 0x00ffffff) == 0) {
+                   /* alpha only difference, convert to luminance */
+                   guint8 alpha = diff_pixel >> 24;
+                   diff_pixel = alpha * 0x010101;
+               }
                row[x] = diff_pixel;
            } else {
                row[x] = 0;