[gnome-panel] status-notifier: cairo wants premultiplied alpha

[Alberts Muktupāvels <muktupavels src gnome org>]

commit d7eeee3b4594814c4b7b18550383631a7a06839a
Author: Colomban Wendling <cwendling hypra fr>
Date:   Tue Jan 24 15:28:40 2017 +0100

    status-notifier: cairo wants premultiplied alpha
    
    ARGBA32 data sent from client is not (and must not be)
    premultiplied alpha.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=777698

 modules/external/status-notifier/sn-item-v0.c |   25 +++++++++++++++++++++++++
 1 files changed, 25 insertions(+), 0 deletions(-)
---
diff --git a/modules/external/status-notifier/sn-item-v0.c b/modules/external/status-notifier/sn-item-v0.c
index ef86a01..4624e16 100644
--- a/modules/external/status-notifier/sn-item-v0.c
+++ b/modules/external/status-notifier/sn-item-v0.c
@@ -310,6 +310,8 @@ surface_from_variant (GVariant *variant,
   cairo_format_t format;
   gint stride;
   guint32 *data;
+  guchar *p;
+  gint y;
 
   format = CAIRO_FORMAT_ARGB32;
   stride = cairo_format_stride_for_width (format, width);
@@ -324,6 +326,29 @@ surface_from_variant (GVariant *variant,
   }
 #endif
 
+  /* CAIRO_FORMAT_ARGB32 wants premultiplied alpha, but data sent from
+   * client is not (and must not be) premultiplied alpha.
+   */
+
+  p = (guchar *) data;
+  for (y = 0; y < height; y++)
+    {
+      gint x;
+
+      for (x = 0; x < width; x++)
+        {
+          guchar alpha;
+
+          alpha = p[x * 4 + 3];
+
+          p[x * 4 + 0] = (p[x * 4 + 0] * alpha) / 255;
+          p[x * 4 + 1] = (p[x * 4 + 1] * alpha) / 255;
+          p[x * 4 + 2] = (p[x * 4 + 2] * alpha) / 255;
+        }
+
+      p += stride;
+    }
+
   return cairo_image_surface_create_for_data ((guchar *) data, format,
                                               width, height, stride);
 }