[gtk+] GtkWidget: Fix clipping to large subwindows

[Alexander Larsson <alexl src gnome org>]

commit 864f7f7ebcf1a11377c388b313465caf05877016
Author: Alexander Larsson <alexl redhat com>
Date:   Mon Oct 28 11:32:51 2013 +0100

    GtkWidget: Fix clipping to large subwindows
    
    _gtk_widget_draw_internal() was clipping by passing the subwindow
    sizes as a path to cairo_clip(). This was breaking for windows
    larger than 23 bits in width/height, due to cairo using fixed point
    (24.8) for the path coordinates.
    
    We fix this by pre-clipping the subwindow region to the existing
    cairo clip region in the full 32bit gdkwindow precision. This fixes
    the GooCanvas Large Items test.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=710958

 gtk/gtkwidget.c |   23 +++++++++++++++++++----
 1 files changed, 19 insertions(+), 4 deletions(-)
---
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 7acfd65..21d02f3 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -6491,18 +6491,33 @@ _gtk_widget_draw_windows (GdkWindow *window,
   gboolean do_clip;
   GtkWidget *widget = NULL;
   GList *children, *l;
+  GdkRectangle current_clip, window_clip;
   int x, y;
 
   if (!gdk_window_is_viewable (window))
     return;
 
+  window_clip.x = window_x;
+  window_clip.y = window_y;
+  window_clip.width = gdk_window_get_width (window);
+  window_clip.height = gdk_window_get_height (window);
+
+  /* Cairo paths are fixed point 24.8, but gdk supports 32bit window
+     sizes, so we can't feed window_clip to e.g. cairo_rectangle()
+     directly. Instead, we pre-clip the window clip to the existing
+     clip regions in full 32bit precision and feed that to cairo. */
+  if (!gdk_cairo_get_clip_rectangle (cr, &current_clip) ||
+      !gdk_rectangle_intersect (&window_clip, &current_clip, &window_clip))
+    return;
+
   cairo_save (cr);
-  cairo_translate (cr, window_x, window_y);
-  cairo_rectangle (cr, 0, 0,
-                  gdk_window_get_width (window),
-                  gdk_window_get_height (window));
+  cairo_rectangle (cr,
+                   window_clip.x, window_clip.y,
+                   window_clip.width, window_clip.height);
   cairo_clip (cr);
 
+  cairo_translate (cr, window_x, window_y);
+
   if (gdk_cairo_get_clip_rectangle (cr, NULL))
     {
       gdk_window_get_user_data (window, (gpointer *) &widget);