[metacity/gnome-3-20] libmetacity: fix gradients

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 4b5175ff8ab044abc8635d3778364dd6001dcf8e
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Thu Jul 7 18:39:54 2016 +0300

    libmetacity: fix gradients

 libmetacity/meta-gradient-spec.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/libmetacity/meta-gradient-spec.c b/libmetacity/meta-gradient-spec.c
index bb6a98d..70affdd 100644
--- a/libmetacity/meta-gradient-spec.c
+++ b/libmetacity/meta-gradient-spec.c
@@ -74,17 +74,23 @@ create_cairo_pattern_from_gradient_spec (const MetaGradientSpec      *spec,
       meta_color_spec_render (tmp->data, context, &color);
 
       if (alpha_spec != NULL)
-        cairo_pattern_add_color_stop_rgba (pattern, i / (gfloat) n_colors,
+        cairo_pattern_add_color_stop_rgba (pattern, i / (gfloat) (n_colors - 1),
                                            color.red, color.green, color.blue,
-                                           alpha_spec->alphas[i]);
+                                           alpha_spec->alphas[i] / 255.0);
       else
-        cairo_pattern_add_color_stop_rgb (pattern, i / (gfloat) n_colors,
+        cairo_pattern_add_color_stop_rgb (pattern, i / (gfloat) (n_colors - 1),
                                           color.red, color.green, color.blue);
 
       tmp = tmp->next;
       ++i;
     }
 
+  if (cairo_pattern_status (pattern) != CAIRO_STATUS_SUCCESS)
+    {
+      cairo_pattern_destroy (pattern);
+      return NULL;
+    }
+
   return pattern;
 }