From f51482e283f7c9c2d7d0e0394dced2ea57d4b67b Mon Sep 17 00:00:00 2001
From: Alexander Larsson <alexl@redhat.com>
Date: Thu, 1 Dec 2011 13:57:27 +0100
Subject: [PATCH] gdk: Track wether windows have alpha in the background

This will let us handle such windows differently in the
drawing machinery
---
 gdk/gdkinternals.h |  1 +
 gdk/gdkwindow.c    | 51 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/gdk/gdkinternals.h b/gdk/gdkinternals.h
index 27afe026ac..9bd1ea9e65 100644
--- a/gdk/gdkinternals.h
+++ b/gdk/gdkinternals.h
@@ -204,6 +204,7 @@ struct _GdkWindow
   guint input_only : 1;
   guint modal_hint : 1;
   guint composited : 1;
+  guint has_alpha_background : 1;
 
   guint destroyed : 2;
 
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index dba089704f..ae0850c58b 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -6476,6 +6476,9 @@ void
 gdk_window_set_background_pattern (GdkWindow *window,
                                    cairo_pattern_t *pattern)
 {
+  gboolean has_alpha;
+  cairo_pattern_type_t type;
+  
   g_return_if_fail (GDK_IS_WINDOW (window));
 
   if (window->input_only)
@@ -6487,6 +6490,54 @@ gdk_window_set_background_pattern (GdkWindow *window,
     cairo_pattern_destroy (window->background);
   window->background = pattern;
 
+  has_alpha = TRUE;
+  type = cairo_pattern_get_type (pattern);
+  
+  if (type == CAIRO_PATTERN_TYPE_SOLID)
+    {
+      double alpha;
+      cairo_pattern_get_rgba (pattern, NULL, NULL, NULL, &alpha);
+      if (alpha == 1.0)
+	has_alpha = FALSE;
+    }
+  else if (type == CAIRO_PATTERN_TYPE_LINEAR ||
+	   type == CAIRO_PATTERN_TYPE_RADIAL)
+    {
+      int i, n;
+      double alpha;
+
+      n = 0;
+      cairo_pattern_get_color_stop_count (pattern, &n);
+      has_alpha = FALSE;
+      for (i = 0; i < n; i++)
+	{
+	  cairo_pattern_get_color_stop_rgba (pattern, i, NULL,
+					     NULL, NULL, NULL, &alpha);
+	  if (alpha != 1.0)
+	    {
+	      has_alpha = TRUE;
+	      break;
+	    }
+	}
+    }
+  else if (type == CAIRO_PATTERN_TYPE_SURFACE)
+    {
+      cairo_surface_t *surface;
+      cairo_content_t content;
+
+      cairo_pattern_get_surface (pattern, &surface);
+      content = cairo_surface_get_content (surface);
+      has_alpha =
+	(content == CAIRO_CONTENT_ALPHA) ||
+	(content == CAIRO_CONTENT_COLOR_ALPHA);
+    }
+  
+  if (has_alpha != window->has_alpha_background)
+    {
+      window->has_alpha_background = has_alpha;  
+      recompute_visible_regions (window, TRUE, FALSE);
+    }
+  
   if (gdk_window_has_impl (window))
     {
       GdkWindowImplClass *impl_class = GDK_WINDOW_IMPL_GET_CLASS (window->impl);
-- 
2.30.2