[vte] app: Fix background image drawing

[Christian Persch <chpe src gnome org>]

commit 79e40dd5387a6a54ce418a082a4ebb6eaf60b20e
Author: Christian Persch <chpe src gnome org>
Date:   Thu Nov 12 22:53:36 2020 +0100

    app: Fix background image drawing
    
    Use the option's background alpha value, *not* the value retrieved from
    vte_terminal_get_color_background_for_draw() since that is set to zero
    in this case.
    
    Fixes a regression from commit eb85292b3ef44ac95d3863af68b19f6a8d8131e2.
    
    Fixes: https://gitlab.gnome.org/GNOME/vte/-/issues/301

 src/app/app.cc | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)
---
diff --git a/src/app/app.cc b/src/app/app.cc
index 7c23c273..789bce7d 100644
--- a/src/app/app.cc
+++ b/src/app/app.cc
@@ -454,6 +454,17 @@ public:
                 return alpha;
         }
 
+        double get_alpha_bg_for_draw() const
+        {
+                double alpha;
+                if (whole_window_transparent)
+                        alpha = 1.0;
+                else
+                        alpha = get_alpha();
+
+                return alpha;
+        }
+
         GdkRGBA get_color_bg() const
         {
                 GdkRGBA color{bg_color};
@@ -1041,7 +1052,7 @@ vteapp_terminal_draw(GtkWidget* widget,
                 cairo_paint(cr);
 
                 cairo_pop_group_to_source(cr);
-                cairo_paint_with_alpha(cr, bg.alpha);
+                cairo_paint_with_alpha(cr, options.get_alpha_bg_for_draw());
 
         }