gdkwindow: Remove the internal cairo_surface used for out-of-band painting

Traditionally, the way painting was done in GTK+ was with the
"expose-event" handler, where you'd use GDK methods to do drawing on
your surface. In GTK+ 2.24, we added cairo support with gdk_cairo_create,
so you could paint your graphics with cairo.

Since then, we've added client-side windows, double buffering, the paint
clock, and various other enhancements, and the modern way to do drawing
is to connect to the "draw" signal on GtkWidget, which hands you a
cairo_t. To do double-buffering, the cairo_t we hand you is actually on
a secret surface, not the actual backing store of the window, and when
the draw handler completes we blit it into the main backing store
atomically.

The code to do this is with the APIs gdk_window_begin_paint_region,
which creates the temporary surface, and gdk_window_end_paint which
blits it back into the backing store. GTK+'s implementation of the
"draw" signal uses these APIs.

We've always sort-of supported people calling gdk_cairo_create
"outside" of a begin_paint / end_paint like old times, but then you're
not getting the benefit of double-buffering, and it's harder for GDK to
optimize.

Additionally, newer backends like Mir and Wayland can't actually support
this model, since they're based on double-buffering and swapping buffers
at various points in time. If we hand you a random cairo_t, we have no
idea when is a good time to swap.

Remove support for this.

This is technically a GDK API break: a warning is added in cases where
gdk_cairo_create is called outside of a paint cycle, and the returned
surface is a dummy that won't ever be composited back onto the main
surface. Testing with complex applications like Ardour didn't produce
any warnings.

9 files changed, 63 insertions, 202 deletions

diff --git a/gdk/broadway/gdkwindow-broadway.c b/gdk/broadway/gdkwindow-broadway.c
index 65ca990aca..d25829f08f 100644
--- a/gdk/broadway/gdkwindow-broadway.c
+++ b/gdk/broadway/gdkwindow-broadway.c
@@ -368,16 +368,6 @@ _gdk_broadway_window_destroy (GdkWindow *window,
 				       impl->id);
 }
 
-static gboolean
-gdk_window_broadway_resize_cairo_surface (GdkWindow       *window,
-					  cairo_surface_t *surface,
-					  gint             width,
-					  gint             height)
-{
-  /* Image surfaces cannot be resized */
-  return FALSE;
-}
-
 static void
 gdk_broadway_window_destroy_foreign (GdkWindow *window)
 {
@@ -1552,7 +1542,6 @@ gdk_window_impl_broadway_class_init (GdkWindowImplBroadwayClass *klass)
   impl_class->queue_antiexpose = _gdk_broadway_window_queue_antiexpose;
   impl_class->destroy = _gdk_broadway_window_destroy;
   impl_class->destroy_foreign = gdk_broadway_window_destroy_foreign;
-  impl_class->resize_cairo_surface = gdk_window_broadway_resize_cairo_surface;
   impl_class->get_shape = gdk_broadway_window_get_shape;
   impl_class->get_input_shape = gdk_broadway_window_get_input_shape;
   impl_class->beep = gdk_broadway_window_beep;
diff --git a/gdk/gdkinternals.h b/gdk/gdkinternals.h
index 3cc26cc6dd..56c7725048 100644
--- a/gdk/gdkinternals.h
+++ b/gdk/gdkinternals.h
@@ -266,8 +266,6 @@ struct _GdkWindow
   cairo_region_t *shape;
   cairo_region_t *input_shape;
 
-  cairo_surface_t *cairo_surface;
-
   GList *devices_inside;
   GHashTable *device_events;
 
diff --git a/gdk/gdkoffscreenwindow.c b/gdk/gdkoffscreenwindow.c
index 74b82bc4c2..5ee179f86d 100644
--- a/gdk/gdkoffscreenwindow.c
+++ b/gdk/gdkoffscreenwindow.c
@@ -549,18 +549,6 @@ gdk_offscreen_window_queue_antiexpose (GdkWindow *window,
   return FALSE;
 }
 
-static gboolean
-gdk_offscreen_window_resize_cairo_surface (GdkWindow       *window,
-                                           cairo_surface_t *surface,
-                                           gint             width,
-                                           gint             height)
-{
-  /* No-op.  The surface gets resized in
-   * gdk_offscreen_window_move_resize_internal().
-   */
-  return TRUE;
-}
-
 /**
  * gdk_offscreen_window_set_embedder:
  * @window: a #GdkWindow
@@ -727,7 +715,6 @@ gdk_offscreen_window_class_init (GdkOffscreenWindowClass *klass)
   impl_class->queue_antiexpose = gdk_offscreen_window_queue_antiexpose;
   impl_class->destroy = gdk_offscreen_window_destroy;
   impl_class->destroy_foreign = NULL;
-  impl_class->resize_cairo_surface = gdk_offscreen_window_resize_cairo_surface;
   impl_class->get_shape = NULL;
   impl_class->get_input_shape = NULL;
   impl_class->beep = NULL;
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index dc658c3eb6..e864606ac0 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -151,12 +151,11 @@ struct _GdkWindowPaint
 {
   cairo_region_t *region;
   cairo_surface_t *surface;
+  gboolean surface_needs_composite;
 };
 
 /* Global info */
 
-static void             gdk_window_drop_cairo_surface (GdkWindow *private);
-
 static void gdk_window_free_paint_stack (GdkWindow *window);
 
 static void gdk_window_finalize   (GObject              *object);
@@ -477,8 +476,6 @@ gdk_window_finalize (GObject *object)
 	_gdk_window_destroy (window, TRUE);
     }
 
-  gdk_window_drop_cairo_surface (window);
-
   if (window->impl)
     {
       g_object_unref (window->impl);
@@ -1002,18 +999,6 @@ recompute_visible_regions_internal (GdkWindow *private,
 					      FALSE);
 	}
     }
-
-  if (private->cairo_surface)
-    {
-      if (!gdk_window_has_impl (private) ||
-          !GDK_WINDOW_IMPL_GET_CLASS (private->impl)->resize_cairo_surface (private,
-                                                                            private->cairo_surface,
-                                                                            private->width,
-                                                                            private->height))
-        {
-          gdk_window_drop_cairo_surface (private);
-        }
-    }
 }
 
 /* Call this when private has changed in one or more of these ways:
@@ -1531,10 +1516,6 @@ gdk_window_reparent (GdkWindow *window,
   if (is_parent_of (window, new_parent))
     return;
 
-  /* This might be wrong in the new parent, e.g. for non-native surfaces.
-     To make sure we're ok, just wipe it. */
-  gdk_window_drop_cairo_surface (window);
-
   impl_class = GDK_WINDOW_IMPL_GET_CLASS (window->impl);
   old_parent = window->parent;
 
@@ -1716,8 +1697,6 @@ gdk_window_ensure_native (GdkWindow *window)
 
   /* Need to create a native window */
 
-  gdk_window_drop_cairo_surface (window);
-
   screen = gdk_window_get_screen (window);
   display = gdk_screen_get_display (screen);
   parent = window->parent;
@@ -1889,7 +1868,6 @@ _gdk_window_destroy_hierarchy (GdkWindow *window,
   if (temp_window == window)
     g_object_set_qdata (G_OBJECT (screen), quark_pointer_window, NULL);
 
-
   switch (window->window_type)
     {
     case GDK_WINDOW_ROOT:
@@ -1987,8 +1965,6 @@ _gdk_window_destroy_hierarchy (GdkWindow *window,
 
 	  _gdk_window_clear_update_area (window);
 
-	  gdk_window_drop_cairo_surface (window);
-
 	  impl_class = GDK_WINDOW_IMPL_GET_CLASS (window->impl);
 
 	  if (gdk_window_has_impl (window))
@@ -2780,6 +2756,12 @@ gdk_window_begin_paint_region (GdkWindow       *window,
       cairo_surface_get_device_scale (paint->surface, &sx, &sy);
 #endif
       cairo_surface_set_device_offset (paint->surface, -clip_box.x*sx, -clip_box.y*sy);
+
+      paint->surface_needs_composite = TRUE;
+    }
+  else
+    {
+      paint->surface = gdk_window_ref_impl_surface (window);
     }
 
   for (list = window->paint_stack; list != NULL; list = list->next)
@@ -2796,6 +2778,23 @@ gdk_window_begin_paint_region (GdkWindow       *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);
+    }
+}
+
 /**
  * gdk_window_end_paint:
  * @window: a #GdkWindow
@@ -2841,14 +2840,18 @@ gdk_window_end_paint (GdkWindow *window)
   window->paint_stack = g_slist_delete_link (window->paint_stack,
 					     window->paint_stack);
 
-
-  if (paint->surface != NULL)
+  if (paint->surface_needs_composite)
     {
+      cairo_surface_t *surface;
+
       cairo_region_get_extents (paint->region, &clip_box);
       full_clip = cairo_region_copy (window->clip_region);
       cairo_region_intersect (full_clip, paint->region);
 
-      cr = gdk_cairo_create (window);
+      surface = get_window_surface (window);
+      cr = cairo_create (surface);
+      cairo_surface_destroy (surface);
+
       cairo_set_source_surface (cr, paint->surface, 0, 0);
       gdk_cairo_region (cr, full_clip);
       cairo_clip (cr);
@@ -2866,10 +2869,10 @@ gdk_window_end_paint (GdkWindow *window)
 
       cairo_destroy (cr);
       cairo_region_destroy (full_clip);
-
-      cairo_surface_destroy (paint->surface);
     }
 
+  cairo_surface_destroy (paint->surface);
+
   cairo_region_destroy (paint->region);
   g_free (paint);
 
@@ -2908,8 +2911,7 @@ gdk_window_free_paint_stack (GdkWindow *window)
 	{
 	  GdkWindowPaint *paint = tmp_list->data;
 
-	  if (tmp_list == window->paint_stack &&
-	      paint->surface != NULL)
+	  if (tmp_list == window->paint_stack)
 	    cairo_surface_destroy (paint->surface);
 
 	  cairo_region_destroy (paint->region);
@@ -3012,7 +3014,7 @@ gdk_window_clear_backing_region (GdkWindow *window,
   int x_offset = 0, y_offset = 0;
   cairo_t *cr;
 
-  if (GDK_WINDOW_DESTROYED (window) || paint->surface == NULL)
+  if (GDK_WINDOW_DESTROYED (window))
     return;
 
   cr = cairo_create (paint->surface);
@@ -3047,88 +3049,23 @@ gdk_window_clear_backing_region (GdkWindow *window,
   cairo_region_destroy (clip);
 }
 
-static void
-gdk_window_drop_cairo_surface (GdkWindow *window)
-{
-  if (window->cairo_surface)
-    {
-      cairo_surface_finish (window->cairo_surface);
-      cairo_surface_set_user_data (window->cairo_surface, &gdk_window_cairo_key,
-				   NULL, NULL);
-      window->cairo_surface = NULL;
-    }
-}
-
-static void
-gdk_window_cairo_surface_destroy (void *data)
-{
-  GdkWindow *window = data;
-
-  window->cairo_surface = NULL;
-}
-
-static cairo_surface_t *
-gdk_window_create_cairo_surface (GdkWindow *window,
-				 int width,
-				 int height)
-{
-  cairo_surface_t *surface, *subsurface;
-
-  surface = gdk_window_ref_impl_surface (window);
-  if (gdk_window_has_impl (window))
-    return surface;
-
-  subsurface = cairo_surface_create_for_rectangle (surface,
-                                                   window->abs_x,
-                                                   window->abs_y,
-                                                   width,
-                                                   height);
-  cairo_surface_destroy (surface);
-  return subsurface;
-}
-
-
+/* 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. */
 cairo_surface_t *
 _gdk_window_ref_cairo_surface (GdkWindow *window)
 {
   cairo_surface_t *surface;
-  GdkWindowPaint *paint;
 
   g_return_val_if_fail (GDK_IS_WINDOW (window), NULL);
 
-  paint = NULL;
-  if (window->impl_window->paint_stack)
-    paint = window->impl_window->paint_stack->data;
-
-  if (paint && paint->surface != NULL)
-    {
-      surface = cairo_surface_create_for_rectangle (paint->surface,
-						    window->abs_x,
-						    window->abs_y,
-						    window->width,
-						    window->height);
-    }
-  else
-    {
-      if (!window->cairo_surface)
-	{
-	  window->cairo_surface = gdk_window_create_cairo_surface (window,
-                                                                   window->width,
-                                                                   window->height);
-
-	  if (window->cairo_surface)
-	    {
-	      cairo_surface_set_user_data (window->cairo_surface, &gdk_window_cairo_key,
-					   window, gdk_window_cairo_surface_destroy);
-	    }
-	}
-      else
-	cairo_surface_reference (window->cairo_surface);
-
-      surface = window->cairo_surface;
-    }
+  surface = get_window_surface (window);
 
-  return surface;
+  return cairo_surface_create_for_rectangle (surface,
+                                             window->abs_x,
+                                             window->abs_y,
+                                             window->width,
+                                             window->height);
 }
 
 /**
@@ -3149,30 +3086,34 @@ cairo_t *
 gdk_cairo_create (GdkWindow *window)
 {
   GdkWindowPaint *paint;
-  cairo_surface_t *surface;
   cairo_region_t *region;
   cairo_t *cr;
 
   g_return_val_if_fail (GDK_IS_WINDOW (window), NULL);
 
-  surface = _gdk_window_ref_cairo_surface (window);
-  cr = cairo_create (surface);
-
-  if (window->impl_window->paint_stack)
+  if (window->impl_window->paint_stack == NULL)
     {
-      paint = window->impl_window->paint_stack->data;
+      cairo_surface_t *dummy_surface;
+      cairo_t *cr;
 
-      region = cairo_region_copy (paint->region);
-      cairo_region_translate (region, -window->abs_x, -window->abs_y);
-      gdk_cairo_region (cr, region);
-      cairo_region_destroy (region);
-   }
-  else
-    gdk_cairo_region (cr, window->clip_region);
+      g_warning ("gdk_cairo_create called from outside a paint. Make sure to call "
+                 "gdk_window_begin_paint_region before calling gdk_cairo_create!");
 
-  cairo_clip (cr);
+      /* Return a dummy surface to keep apps from crashing. */
+      dummy_surface = cairo_image_surface_create (gdk_window_get_content (window), 0, 0);
+      cr = cairo_create (dummy_surface);
+      cairo_surface_destroy (dummy_surface);
+      return cr;
+    }
 
-  cairo_surface_destroy (surface);
+  paint = window->impl_window->paint_stack->data;
+
+  cr = cairo_create (paint->surface);
+  region = cairo_region_copy (paint->region);
+  cairo_region_translate (region, -window->abs_x, -window->abs_y);
+  gdk_cairo_region (cr, region);
+  cairo_region_destroy (region);
+  cairo_clip (cr);
 
   return cr;
 }
diff --git a/gdk/gdkwindowimpl.h b/gdk/gdkwindowimpl.h
index b1e9290bc1..694a244761 100644
--- a/gdk/gdkwindowimpl.h
+++ b/gdk/gdkwindowimpl.h
@@ -158,15 +158,6 @@ struct _GdkWindowImplClass
   */
   void         (*destroy_foreign)       (GdkWindow       *window);
 
-  /* Resizes @surface to a new size. If successful, return %TRUE.
-   * If the backend cannot resize surfaces, return %FALSE and a new
-   * surface will be created instead.
-   */
-  gboolean     (* resize_cairo_surface) (GdkWindow       *window,
-                                         cairo_surface_t *surface,
-                                         gint             width,
-                                         gint             height);
-
   /* optional */
   gboolean     (* beep)                 (GdkWindow       *window);
 
diff --git a/gdk/quartz/gdkwindow-quartz.c b/gdk/quartz/gdkwindow-quartz.c
index 84e7ab871d..37efa7ccca 100644
--- a/gdk/quartz/gdkwindow-quartz.c
+++ b/gdk/quartz/gdkwindow-quartz.c
@@ -1104,16 +1104,6 @@ gdk_quartz_window_destroy (GdkWindow *window,
     }
 }
 
-static gboolean
-gdk_window_quartz_resize_cairo_surface (GdkWindow       *window,
-                                        cairo_surface_t *surface,
-                                        gint             width,
-                                        gint             height)
-{
-  /* Quartz surfaces cannot be resized */
-  return FALSE;
-}
-
 static void
 gdk_quartz_window_destroy_foreign (GdkWindow *window)
 {
@@ -2949,7 +2939,6 @@ gdk_window_impl_quartz_class_init (GdkWindowImplQuartzClass *klass)
   impl_class->queue_antiexpose = gdk_quartz_window_queue_antiexpose;
   impl_class->destroy = gdk_quartz_window_destroy;
   impl_class->destroy_foreign = gdk_quartz_window_destroy_foreign;
-  impl_class->resize_cairo_surface = gdk_window_quartz_resize_cairo_surface;
   impl_class->get_shape = gdk_quartz_window_get_shape;
   impl_class->get_input_shape = gdk_quartz_window_get_input_shape;
   impl_class->begin_paint_region = gdk_window_impl_quartz_begin_paint_region;
diff --git a/gdk/wayland/gdkwindow-wayland.c b/gdk/wayland/gdkwindow-wayland.c
index 461d1ce9d7..a3058de847 100644
--- a/gdk/wayland/gdkwindow-wayland.c
+++ b/gdk/wayland/gdkwindow-wayland.c
@@ -1350,16 +1350,6 @@ gdk_window_wayland_destroy_foreign (GdkWindow *window)
 {
 }
 
-static gboolean
-gdk_window_wayland_resize_cairo_surface (GdkWindow       *window,
-                                         cairo_surface_t *surface,
-                                         gint             width,
-                                         gint             height)
-{
-  /* cairo image surfaces cannot be resized */
-  return FALSE;
-}
-
 static cairo_region_t *
 gdk_wayland_window_get_shape (GdkWindow *window)
 {
@@ -1994,7 +1984,6 @@ _gdk_window_impl_wayland_class_init (GdkWindowImplWaylandClass *klass)
   impl_class->queue_antiexpose = gdk_wayland_window_queue_antiexpose;
   impl_class->destroy = gdk_wayland_window_destroy;
   impl_class->destroy_foreign = gdk_window_wayland_destroy_foreign;
-  impl_class->resize_cairo_surface = gdk_window_wayland_resize_cairo_surface;
   impl_class->get_shape = gdk_wayland_window_get_shape;
   impl_class->get_input_shape = gdk_wayland_window_get_input_shape;
   impl_class->begin_paint_region = gdk_window_impl_wayland_begin_paint_region;
diff --git a/gdk/win32/gdkwindow-win32.c b/gdk/win32/gdkwindow-win32.c
index aa8f5916ea..23e1848c02 100644
--- a/gdk/win32/gdkwindow-win32.c
+++ b/gdk/win32/gdkwindow-win32.c
@@ -796,16 +796,6 @@ gdk_win32_window_destroy (GdkWindow *window,
     }
 }
 
-static gboolean
-gdk_win32_window_resize_cairo_surface (GdkWindow       *window,
-                                       cairo_surface_t *surface,
-                                       gint             width,
-                                       gint             height)
-{
-  /* XXX: Make Cairo surface use DC clip */
-  return FALSE;
-}
-
 static void
 gdk_win32_window_destroy_foreign (GdkWindow *window)
 {
@@ -3433,7 +3423,6 @@ gdk_window_impl_win32_class_init (GdkWindowImplWin32Class *klass)
   impl_class->queue_antiexpose = _gdk_win32_window_queue_antiexpose;
   impl_class->destroy = gdk_win32_window_destroy;
   impl_class->destroy_foreign = gdk_win32_window_destroy_foreign;
-  impl_class->resize_cairo_surface = gdk_win32_window_resize_cairo_surface;
   impl_class->get_shape = gdk_win32_window_get_shape;
   //FIXME?: impl_class->get_input_shape = gdk_win32_window_get_input_shape;
 
diff --git a/gdk/x11/gdkwindow-x11.c b/gdk/x11/gdkwindow-x11.c
index 1fa3afc2aa..3c7c6cc59d 100644
--- a/gdk/x11/gdkwindow-x11.c
+++ b/gdk/x11/gdkwindow-x11.c
@@ -1337,17 +1337,6 @@ gdk_x11_window_destroy (GdkWindow *window,
     XDestroyWindow (GDK_WINDOW_XDISPLAY (window), GDK_WINDOW_XID (window));
 }
 
-static gboolean
-gdk_window_x11_resize_cairo_surface (GdkWindow       *window,
-                                     cairo_surface_t *surface,
-                                     gint             width,
-                                     gint             height)
-{
-  cairo_xlib_surface_set_size (surface, width, height);
-
-  return TRUE;
-}
-
 static void
 gdk_x11_window_destroy_foreign (GdkWindow *window)
 {
@@ -5780,7 +5769,6 @@ gdk_window_impl_x11_class_init (GdkWindowImplX11Class *klass)
   impl_class->queue_antiexpose = _gdk_x11_window_queue_antiexpose;
   impl_class->destroy = gdk_x11_window_destroy;
   impl_class->destroy_foreign = gdk_x11_window_destroy_foreign;
-  impl_class->resize_cairo_surface = gdk_window_x11_resize_cairo_surface;
   impl_class->get_shape = gdk_x11_window_get_shape;
   impl_class->get_input_shape = gdk_x11_window_get_input_shape;
   impl_class->beep = gdk_x11_window_beep;