[gtk+] gdkwindow: Remove the ability to call begin_paint_region more than once

[Jasper St. Pierre <jstpierre src gnome org>]

commit be30e440c350f0f3e0f2572f7f3eab54ef96af0e
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Fri Jun 20 20:20:14 2014 -0400

    gdkwindow: Remove the ability to call begin_paint_region more than once
    
    Previously, each begin_paint_region added to a stack of current paints,
    and when end_paint was called, the paint was popped off of the stack and
    the surface was composited into the parent paint surface.
    
    However, the code was broken in the case of a backend like Wayland which
    didn't keep track of nested calls and simply wiped and returned the
    native impl backing surface every time.
    
    Since this feature is flat out unused by GTK+ and we don't want to
    really support tricksy things like these for other clients, just remove
    the feature. If somebody does call begin_paint_region more than once,
    warn and return without doing anything.

 gdk/gdkinternals.h            |    6 +-
 gdk/gdkwindow.c               |  180 ++++++++++++++---------------------------
 gdk/quartz/gdkwindow-quartz.c |   47 +----------
 gdk/quartz/gdkwindow-quartz.h |    1 -
 4 files changed, 68 insertions(+), 166 deletions(-)
---
diff --git a/gdk/gdkinternals.h b/gdk/gdkinternals.h
index 56c7725..32754a3 100644
--- a/gdk/gdkinternals.h
+++ b/gdk/gdkinternals.h
@@ -205,7 +205,11 @@ struct _GdkWindow
 
   cairo_pattern_t *background;
 
-  GSList *paint_stack;
+  struct {
+    cairo_region_t *region;
+    cairo_surface_t *surface;
+    gboolean surface_needs_composite;
+  } current_paint;
 
   cairo_region_t *update_area;
   guint update_freeze_count;
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index e864606..2853a30 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -147,17 +147,8 @@ enum {
   PROP_CURSOR
 };
 
-struct _GdkWindowPaint
-{
-  cairo_region_t *region;
-  cairo_surface_t *surface;
-  gboolean surface_needs_composite;
-};
-
 /* Global info */
 
-static void gdk_window_free_paint_stack (GdkWindow *window);
-
 static void gdk_window_finalize   (GObject              *object);
 
 static void gdk_window_set_property (GObject      *object,
@@ -1826,6 +1817,18 @@ window_remove_from_pointer_info (GdkWindow  *window,
                                      window);
 }
 
+static void
+gdk_window_free_current_paint (GdkWindow *window)
+{
+  cairo_surface_destroy (window->current_paint.surface);
+  window->current_paint.surface = NULL;
+
+  cairo_region_destroy (window->current_paint.region);
+  window->current_paint.region = NULL;
+
+  window->current_paint.surface_needs_composite = FALSE;
+}
+
 /**
  * _gdk_window_destroy_hierarchy:
  * @window: a #GdkWindow
@@ -1930,7 +1933,7 @@ _gdk_window_destroy_hierarchy (GdkWindow *window,
               gdk_window_set_frame_clock (window, NULL);
             }
 
-         gdk_window_free_paint_stack (window);
+          gdk_window_free_current_paint (window);
 
           if (window->background)
             {
@@ -2722,8 +2725,6 @@ gdk_window_begin_paint_region (GdkWindow       *window,
 {
   GdkRectangle clip_box;
   GdkWindowImplClass *impl_class;
-  GdkWindowPaint *paint;
-  GSList *list;
   double sx, sy;
   gboolean needs_surface;
 
@@ -2733,66 +2734,46 @@ gdk_window_begin_paint_region (GdkWindow       *window,
       !gdk_window_has_impl (window))
     return;
 
+  if (window->current_paint.surface != NULL)
+    {
+      g_warning ("gdk_window_begin_paint_region called while a paint was "
+                 "alredy in progress. This is not allowed.");
+      return;
+    }
+
   impl_class = GDK_WINDOW_IMPL_GET_CLASS (window->impl);
 
   needs_surface = TRUE;
   if (impl_class->begin_paint_region)
     needs_surface = impl_class->begin_paint_region (window, region);
 
-  paint = g_new0 (GdkWindowPaint, 1);
-  paint->region = cairo_region_copy (region);
+  window->current_paint.region = cairo_region_copy (region);
 
-  cairo_region_intersect (paint->region, window->clip_region);
-  cairo_region_get_extents (paint->region, &clip_box);
+  cairo_region_intersect (window->current_paint.region, window->clip_region);
+  cairo_region_get_extents (window->current_paint.region, &clip_box);
 
   if (needs_surface)
     {
-      paint->surface = gdk_window_create_similar_surface (window,
-                                                         gdk_window_get_content (window),
-                                                         MAX (clip_box.width, 1),
-                                                         MAX (clip_box.height, 1));
+      window->current_paint.surface = gdk_window_create_similar_surface (window,
+                                                                         gdk_window_get_content (window),
+                                                                         MAX (clip_box.width, 1),
+                                                                         MAX (clip_box.height, 1));
       sx = sy = 1;
 #ifdef HAVE_CAIRO_SURFACE_SET_DEVICE_SCALE
-      cairo_surface_get_device_scale (paint->surface, &sx, &sy);
+      cairo_surface_get_device_scale (window->current_paint.surface, &sx, &sy);
 #endif
-      cairo_surface_set_device_offset (paint->surface, -clip_box.x*sx, -clip_box.y*sy);
+      cairo_surface_set_device_offset (window->current_paint.surface, -clip_box.x*sx, -clip_box.y*sy);
 
-      paint->surface_needs_composite = TRUE;
+      window->current_paint.surface_needs_composite = TRUE;
     }
   else
     {
-      paint->surface = gdk_window_ref_impl_surface (window);
-    }
-
-  for (list = window->paint_stack; list != NULL; list = list->next)
-    {
-      GdkWindowPaint *tmp_paint = list->data;
-
-      cairo_region_subtract (tmp_paint->region, paint->region);
+      window->current_paint.surface = gdk_window_ref_impl_surface (window);
+      window->current_paint.surface_needs_composite = FALSE;
     }
 
-  window->paint_stack = g_slist_prepend (window->paint_stack, paint);
-
-  if (!cairo_region_is_empty (paint->region))
-    gdk_window_clear_backing_region (window,
-                                    paint->region);
-}
-
-/* This returns either the current working surface on the paint stack
- * or the actual impl surface of the window. This should not be used
- * from very many places: be careful! */
-static cairo_surface_t *
-get_window_surface (GdkWindow *window)
-{
-  if (window->impl_window->paint_stack)
-    {
-      GdkWindowPaint *paint = window->impl_window->paint_stack->data;
-      return cairo_surface_reference (paint->surface);
-    }
-  else
-    {
-      return gdk_window_ref_impl_surface (window);
-    }
+  if (!cairo_region_is_empty (window->current_paint.region))
+    gdk_window_clear_backing_region (window, window->current_paint.region);
 }
 
 /**
@@ -2812,7 +2793,6 @@ void
 gdk_window_end_paint (GdkWindow *window)
 {
   GdkWindow *composited;
-  GdkWindowPaint *paint;
   GdkWindowImplClass *impl_class;
   GdkRectangle clip_box = { 0, };
   cairo_region_t *full_clip;
@@ -2824,7 +2804,7 @@ gdk_window_end_paint (GdkWindow *window)
       !gdk_window_has_impl (window))
     return;
 
-  if (window->paint_stack == NULL)
+  if (window->current_paint.surface == NULL)
     {
       g_warning (G_STRLOC": no preceding call to gdk_window_begin_paint_region(), see documentation");
       return;
@@ -2835,24 +2815,19 @@ gdk_window_end_paint (GdkWindow *window)
   if (impl_class->end_paint)
     impl_class->end_paint (window);
 
-  paint = window->paint_stack->data;
-
-  window->paint_stack = g_slist_delete_link (window->paint_stack,
-                                            window->paint_stack);
-
-  if (paint->surface_needs_composite)
+  if (window->current_paint.surface_needs_composite)
     {
       cairo_surface_t *surface;
 
-      cairo_region_get_extents (paint->region, &clip_box);
+      cairo_region_get_extents (window->current_paint.region, &clip_box);
       full_clip = cairo_region_copy (window->clip_region);
-      cairo_region_intersect (full_clip, paint->region);
+      cairo_region_intersect (full_clip, window->current_paint.region);
 
-      surface = get_window_surface (window);
+      surface = gdk_window_ref_impl_surface (window);
       cr = cairo_create (surface);
       cairo_surface_destroy (surface);
 
-      cairo_set_source_surface (cr, paint->surface, 0, 0);
+      cairo_set_source_surface (cr, window->current_paint.surface, 0, 0);
       gdk_cairo_region (cr, full_clip);
       cairo_clip (cr);
       if (gdk_window_has_impl (window) ||
@@ -2871,10 +2846,7 @@ gdk_window_end_paint (GdkWindow *window)
       cairo_region_destroy (full_clip);
     }
 
-  cairo_surface_destroy (paint->surface);
-
-  cairo_region_destroy (paint->region);
-  g_free (paint);
+  gdk_window_free_current_paint (window);
 
   /* find a composited window in our hierarchy to signal its
    * parent to redraw, calculating the clip box as we go...
@@ -2900,31 +2872,6 @@ gdk_window_end_paint (GdkWindow *window)
     }
 }
 
-static void
-gdk_window_free_paint_stack (GdkWindow *window)
-{
-  if (window->paint_stack)
-    {
-      GSList *tmp_list = window->paint_stack;
-
-      while (tmp_list)
-       {
-         GdkWindowPaint *paint = tmp_list->data;
-
-         if (tmp_list == window->paint_stack)
-           cairo_surface_destroy (paint->surface);
-
-         cairo_region_destroy (paint->region);
-         g_free (paint);
-
-         tmp_list = tmp_list->next;
-       }
-
-      g_slist_free (window->paint_stack);
-      window->paint_stack = NULL;
-    }
-}
-
 /**
  * gdk_window_flush:
  * @window: a #GdkWindow
@@ -2962,23 +2909,8 @@ gdk_window_get_clip_region (GdkWindow *window)
 
   result = cairo_region_copy (window->clip_region);
 
-  if (window->paint_stack)
-    {
-      cairo_region_t *paint_region = cairo_region_create ();
-      GSList *tmp_list = window->paint_stack;
-
-      while (tmp_list)
-       {
-         GdkWindowPaint *paint = tmp_list->data;
-
-         cairo_region_union (paint_region, paint->region);
-
-         tmp_list = tmp_list->next;
-       }
-
-      cairo_region_intersect (result, paint_region);
-      cairo_region_destroy (paint_region);
-    }
+  if (window->current_paint.region != NULL)
+    cairo_region_intersect (result, window->current_paint.region);
 
   return result;
 }
@@ -3007,7 +2939,6 @@ static void
 gdk_window_clear_backing_region (GdkWindow *window,
                                 cairo_region_t *region)
 {
-  GdkWindowPaint *paint = window->paint_stack->data;
   cairo_region_t *clip;
   GdkWindow *bg_window;
   cairo_pattern_t *pattern = NULL;
@@ -3017,7 +2948,7 @@ gdk_window_clear_backing_region (GdkWindow *window,
   if (GDK_WINDOW_DESTROYED (window))
     return;
 
-  cr = cairo_create (paint->surface);
+  cr = cairo_create (window->current_paint.surface);
 
   for (bg_window = window; bg_window; bg_window = bg_window->parent)
     {
@@ -3038,7 +2969,7 @@ gdk_window_clear_backing_region (GdkWindow *window,
   else
     cairo_set_source_rgb (cr, 0, 0, 0);
 
-  clip = cairo_region_copy (paint->region);
+  clip = cairo_region_copy (window->current_paint.region);
   cairo_region_intersect (clip, region);
 
   gdk_cairo_region (cr, clip);
@@ -3049,6 +2980,18 @@ gdk_window_clear_backing_region (GdkWindow *window,
   cairo_region_destroy (clip);
 }
 
+/* This returns either the current working surface on the paint stack
+ * or the actual impl surface of the window. This should not be used
+ * from very many places: be careful! */
+static cairo_surface_t *
+get_window_surface (GdkWindow *window)
+{
+  if (window->impl_window->current_paint.surface)
+    return cairo_surface_reference (window->impl_window->current_paint.surface);
+  else
+    return gdk_window_ref_impl_surface (window);
+}
+
 /* This is used in places like gdk_cairo_set_source_window and
  * other places to take "screenshots" of windows. Thus, we allow
  * it to be used outside of a begin_paint / end_paint. */
@@ -3085,13 +3028,12 @@ _gdk_window_ref_cairo_surface (GdkWindow *window)
 cairo_t *
 gdk_cairo_create (GdkWindow *window)
 {
-  GdkWindowPaint *paint;
   cairo_region_t *region;
   cairo_t *cr;
 
   g_return_val_if_fail (GDK_IS_WINDOW (window), NULL);
 
-  if (window->impl_window->paint_stack == NULL)
+  if (window->impl_window->current_paint.surface == NULL)
     {
       cairo_surface_t *dummy_surface;
       cairo_t *cr;
@@ -3106,10 +3048,8 @@ gdk_cairo_create (GdkWindow *window)
       return cr;
     }
 
-  paint = window->impl_window->paint_stack->data;
-
-  cr = cairo_create (paint->surface);
-  region = cairo_region_copy (paint->region);
+  cr = cairo_create (window->impl_window->current_paint.surface);
+  region = cairo_region_copy (window->impl_window->current_paint.region);
   cairo_region_translate (region, -window->abs_x, -window->abs_y);
   gdk_cairo_region (cr, region);
   cairo_region_destroy (region);
diff --git a/gdk/quartz/gdkwindow-quartz.c b/gdk/quartz/gdkwindow-quartz.c
index 37efa7c..50d6865 100644
--- a/gdk/quartz/gdkwindow-quartz.c
+++ b/gdk/quartz/gdkwindow-quartz.c
@@ -137,37 +137,6 @@ gdk_window_impl_quartz_get_context (GdkWindowImplQuartz *window_impl,
   CGContextSaveGState (cg_context);
   CGContextSetAllowsAntialiasing (cg_context, antialias);
 
-  /* We'll emulate the clipping caused by double buffering here */
-  if (window_impl->begin_paint_count != 0)
-    {
-      CGRect rect;
-      CGRect *cg_rects;
-      gint n_rects, i;
-
-      n_rects = cairo_region_num_rectangles (window_impl->paint_clip_region);
-
-      if (n_rects == 1)
-       cg_rects = &rect;
-      else
-       cg_rects = g_new (CGRect, n_rects);
-
-      for (i = 0; i < n_rects; i++)
-       {
-          cairo_rectangle_int_t cairo_rect;
-          cairo_region_get_rectangle (window_impl->paint_clip_region,
-                                      i, &cairo_rect);
-         cg_rects[i].origin.x = cairo_rect.x;
-         cg_rects[i].origin.y = cairo_rect.y;
-         cg_rects[i].size.width = cairo_rect.width;
-         cg_rects[i].size.height = cairo_rect.height;
-       }
-
-      CGContextClipToRects (cg_context, cg_rects, n_rects);
-
-      if (cg_rects != &rect)
-        g_free (cg_rects);
-    }
-
   return cg_context;
 }
 
@@ -379,12 +348,7 @@ gdk_window_impl_quartz_begin_paint_region (GdkWindow       *window,
   cairo_region_translate (clipped_and_offset_region,
                      window->abs_x, window->abs_y);
 
-  if (impl->begin_paint_count == 0)
-    impl->paint_clip_region = cairo_region_reference (clipped_and_offset_region);
-  else
-    cairo_region_union (impl->paint_clip_region, clipped_and_offset_region);
-
-  impl->begin_paint_count++;
+  impl->paint_clip_region = cairo_region_reference (clipped_and_offset_region);
 
   if (cairo_region_is_empty (clipped_and_offset_region))
     goto done;
@@ -423,13 +387,8 @@ gdk_window_impl_quartz_end_paint (GdkWindow *window)
 {
   GdkWindowImplQuartz *impl = GDK_WINDOW_IMPL_QUARTZ (window->impl);
 
-  impl->begin_paint_count--;
-
-  if (impl->begin_paint_count == 0)
-    {
-      cairo_region_destroy (impl->paint_clip_region);
-      impl->paint_clip_region = NULL;
-    }
+  cairo_region_destroy (impl->paint_clip_region);
+  impl->paint_clip_region = NULL;
 }
 
 static void
diff --git a/gdk/quartz/gdkwindow-quartz.h b/gdk/quartz/gdkwindow-quartz.h
index 396035d..d1b5665 100644
--- a/gdk/quartz/gdkwindow-quartz.h
+++ b/gdk/quartz/gdkwindow-quartz.h
@@ -51,7 +51,6 @@ struct _GdkWindowImplQuartz
   GdkWindowTypeHint type_hint;
 
   cairo_region_t *paint_clip_region;
-  gint begin_paint_count;
   gint in_paint_rect_count;
 
   GdkWindow *transient_for;