[mutter] theme: Take invisible borders required by the theme into account

[Florian Müllner <fmuellner src gnome org>]

commit f9db65f47f7e3cfa050d3373d1a2b3615c574040
Author: Florian Müllner <fmuellner gnome org>
Date:   Wed Jan 20 18:01:41 2016 +0100

    theme: Take invisible borders required by the theme into account
    
    GTK+ paints some elements like box shadows (which Adwaita likes to (ab)use
    for borders) outside the rectangle passed to gtk_render_*. This is not
    an issue if our own invisible frame border is big enough, but in case
    of non-resizable windows we end up clipping away part of the decoration.
    Use the newly added gtk_render_background_get_clip() to make sure we
    always use a mask that is large enough to contain all decorations.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=752794

 configure.ac           |    2 +-
 src/ui/theme-private.h |    2 ++
 src/ui/theme.c         |   20 ++++++++++++++++----
 3 files changed, 19 insertions(+), 5 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 3ad43df..8731079 100644
--- a/configure.ac
+++ b/configure.ac
@@ -59,7 +59,7 @@ CANBERRA_GTK_VERSION=0.26
 CLUTTER_PACKAGE=clutter-1.0
 
 MUTTER_PC_MODULES="
-   gtk+-3.0 >= 3.19.7
+   gtk+-3.0 >= 3.19.8
    gio-unix-2.0 >= 2.35.1
    pango >= 1.2.0
    cairo >= 1.10.0
diff --git a/src/ui/theme-private.h b/src/ui/theme-private.h
index 3ebe06b..eaee95d 100644
--- a/src/ui/theme-private.h
+++ b/src/ui/theme-private.h
@@ -53,6 +53,8 @@ typedef struct _MetaFrameGeometry MetaFrameGeometry;
  **/
 struct _MetaFrameLayout
 {
+  /** Invisible border required by the theme */
+  GtkBorder invisible_border;
   /** Border/padding of the entire frame */
   GtkBorder frame_border;
   /** Border/padding of the titlebar region */
diff --git a/src/ui/theme.c b/src/ui/theme.c
index 71ddf45..0dbfdf6 100644
--- a/src/ui/theme.c
+++ b/src/ui/theme.c
@@ -94,23 +94,28 @@ meta_frame_layout_get_borders (const MetaFrameLayout *layout,
   borders->visible.right  = layout->frame_border.right;
   borders->visible.bottom = layout->frame_border.bottom;
 
+  borders->invisible = layout->invisible_border;
+
   draggable_borders = meta_prefs_get_draggable_border_width ();
 
   if (flags & META_FRAME_ALLOWS_HORIZONTAL_RESIZE)
     {
-      borders->invisible.left   = MAX (0, draggable_borders - borders->visible.left);
-      borders->invisible.right  = MAX (0, draggable_borders - borders->visible.right);
+      borders->invisible.left   = MAX (borders->invisible.left,
+                                       draggable_borders - borders->visible.left);
+      borders->invisible.right  = MAX (borders->invisible.right,
+                                       draggable_borders - borders->visible.right);
     }
 
   if (flags & META_FRAME_ALLOWS_VERTICAL_RESIZE)
     {
-      borders->invisible.bottom = MAX (0, draggable_borders - borders->visible.bottom);
+      borders->invisible.bottom = MAX (borders->invisible.bottom,
+                                       draggable_borders - borders->visible.bottom);
 
       /* borders.visible.top is the height of the *title bar*. We can't do the same
        * algorithm here, titlebars are expectedly much bigger. Just subtract a couple
        * pixels to get a proper feel. */
       if (type != META_FRAME_TYPE_ATTACHED)
-        borders->invisible.top    = MAX (0, draggable_borders - 2);
+        borders->invisible.top    = MAX (borders->invisible.top, draggable_borders - 2);
     }
 
   borders->total.left   = borders->invisible.left   + borders->visible.left;
@@ -266,6 +271,7 @@ meta_frame_layout_sync_with_style (MetaFrameLayout *layout,
   GtkStyleContext *style;
   GtkBorder border;
   GtkRequisition requisition;
+  GdkRectangle clip_rect;
   int border_radius, max_radius;
 
   meta_style_info_set_flags (style_info, flags);
@@ -274,6 +280,12 @@ meta_frame_layout_sync_with_style (MetaFrameLayout *layout,
   get_padding_and_border (style, &layout->frame_border);
   scale_border (&layout->frame_border, layout->title_scale);
 
+  gtk_render_background_get_clip (style, 0, 0, 0, 0, &clip_rect);
+  layout->invisible_border.left = -clip_rect.x;
+  layout->invisible_border.right = clip_rect.width + clip_rect.x;
+  layout->invisible_border.top = -clip_rect.y;
+  layout->invisible_border.bottom = clip_rect.height + clip_rect.y;
+
   if (layout->hide_buttons)
     layout->icon_size = 0;