[gtk+/transparent-windows: 4/8] gdk: Track the layered area

[Alexander Larsson <alexl src gnome org>]

commit 46d5b89830c555bb50af5be848b4415381971924
Author: Alexander Larsson <alexl redhat com>
Date:   Thu Dec 1 13:57:47 2011 +0100

    gdk: Track the layered area
    
    We track the areas that have alpha coverage so that we can
    avoid using these as sources when copying window contents.
    We also don't remove such areas from the clipping regions so
    that they are painted both by parent and child.

 gdk/gdkinternals.h |   13 +++++++++++--
 gdk/gdkwindow.c    |   42 ++++++++++++++++++++++++++++++------------
 2 files changed, 41 insertions(+), 14 deletions(-)
---
diff --git a/gdk/gdkinternals.h b/gdk/gdkinternals.h
index 9bd1ea9..8567fd4 100644
--- a/gdk/gdkinternals.h
+++ b/gdk/gdkinternals.h
@@ -229,8 +229,17 @@ struct _GdkWindow
   gint abs_x, abs_y; /* Absolute offset in impl */
   gint width, height;
 
-  cairo_region_t *clip_region; /* Clip region (wrt toplevel) in window coords */
-  cairo_region_t *clip_region_with_children; /* Clip region in window coords */
+  /* The clip region is the part of the window, in window coordinates
+     that is fully or partially (i.e. semi transparently) visible in
+     the window hierarchy from the toplevel and down */
+  cairo_region_t *clip_region;
+  /* This is the clip region, with additionally all the opaque
+     child windows removed */
+  cairo_region_t *clip_region_with_children;
+  /* The layered region is the subset of clip_region that
+     is covered by non-opaque sibling or ancestor sibling window. */
+  cairo_region_t *layered_region;
+
   GdkCursor *cursor;
   GHashTable *device_cursor;
 
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index ae0850c..d1ac763 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -652,7 +652,8 @@ static void
 remove_child_area (GdkWindow *private,
 		   GdkWindow *until,
 		   gboolean for_input,
-		   cairo_region_t *region)
+		   cairo_region_t *region,
+		   cairo_region_t *layered_region)
 {
   GdkWindow *child;
   cairo_region_t *child_region;
@@ -723,7 +724,13 @@ remove_child_area (GdkWindow *private,
 	    }
 	}
 
-      cairo_region_subtract (region, child_region);
+      if (child->has_alpha_background)
+	{
+	  if (layered_region != NULL)
+	    cairo_region_union (layered_region, child_region);
+	}
+      else
+	cairo_region_subtract (region, child_region);
       cairo_region_destroy (child_region);
 
     }
@@ -868,7 +875,7 @@ recompute_visible_regions_internal (GdkWindow *private,
   GdkRectangle r;
   GList *l;
   GdkWindow *child;
-  cairo_region_t *new_clip, *old_clip_region_with_children;
+  cairo_region_t *new_clip, *new_layered;
   gboolean clip_region_changed;
   gboolean abs_pos_changed;
   int old_abs_x, old_abs_y;
@@ -901,6 +908,7 @@ recompute_visible_regions_internal (GdkWindow *private,
   clip_region_changed = FALSE;
   if (recalculate_clip)
     {
+      new_layered = cairo_region_create ();
       if (private->viewable)
 	{
 	  /* Calculate visible region (sans children) in parent window coords */
@@ -913,35 +921,45 @@ recompute_visible_regions_internal (GdkWindow *private,
 	  if (!gdk_window_is_toplevel (private))
 	    {
 	      cairo_region_intersect (new_clip, private->parent->clip_region);
+	      cairo_region_union (new_layered, private->parent->layered_region);
 
 	      /* Remove all overlapping children from parent. */
-	      remove_child_area (private->parent, private, FALSE, new_clip);
+	      remove_child_area (private->parent, private, FALSE, new_clip, new_layered);
 	    }
 
 	  /* Convert from parent coords to window coords */
 	  cairo_region_translate (new_clip, -private->x, -private->y);
+	  cairo_region_translate (new_layered, -private->x, -private->y);
 
 	  if (private->shape)
 	    cairo_region_intersect (new_clip, private->shape);
 	}
       else
-	new_clip = cairo_region_create ();
+	  new_clip = cairo_region_create ();
 
+      cairo_region_intersect (new_layered, new_clip);
+      
       if (private->clip_region == NULL ||
 	  !cairo_region_equal (private->clip_region, new_clip))
 	clip_region_changed = TRUE;
 
+      if (private->layered_region == NULL ||
+	  !cairo_region_equal (private->layered_region, new_layered))
+	clip_region_changed = TRUE;
+      
       if (private->clip_region)
 	cairo_region_destroy (private->clip_region);
       private->clip_region = new_clip;
 
-      old_clip_region_with_children = private->clip_region_with_children;
+      if (private->layered_region != NULL)
+	cairo_region_destroy (private->layered_region);
+      private->layered_region = new_layered;
+
+      if (private->clip_region_with_children)
+	cairo_region_destroy (private->clip_region_with_children);
       private->clip_region_with_children = cairo_region_copy (private->clip_region);
       if (private->window_type != GDK_WINDOW_ROOT)
-	remove_child_area (private, NULL, FALSE, private->clip_region_with_children);
-
-      if (old_clip_region_with_children)
-	cairo_region_destroy (old_clip_region_with_children);
+	remove_child_area (private, NULL, FALSE, private->clip_region_with_children, NULL);
     }
 
   if (clip_region_changed)
@@ -7163,7 +7181,7 @@ do_child_shapes (GdkWindow *window,
   r.height = window->height;
 
   region = cairo_region_create_rectangle (&r);
-  remove_child_area (window, NULL, FALSE, region);
+  remove_child_area (window, NULL, FALSE, region, NULL);
 
   if (merge && window->shape)
     cairo_region_subtract (region, window->shape);
@@ -7282,7 +7300,7 @@ do_child_input_shapes (GdkWindow *window,
   r.height = window->height;
 
   region = cairo_region_create_rectangle (&r);
-  remove_child_area (window, NULL, TRUE, region);
+  remove_child_area (window, NULL, TRUE, region, NULL);
 
   if (merge && window->shape)
     cairo_region_subtract (region, window->shape);