stylecontext: Add an animating framework

The design principles were:

- synchronized
If multiple style contexts are animating, they should all do an
animation step at the same time.

- degrades well
Even when there's thousands of style contexts all animating at the same
time, the animation steps don't starve the CPU. This is achieved by
making sure the timeout is really fast. It just sets a bunch of flags.

- no hidden bottlenecks
Turning animatability on or off on a style context is O(1).

So far it is unused.

gtk/gtkcsstypes.c

@@ -56,7 +56,8 @@ _gtk_css_change_for_sibling (GtkCssChange match)
     { GTK_CSS_CHANGE_NAME, GTK_CSS_CHANGE_SIBLING_NAME },
     { GTK_CSS_CHANGE_POSITION, GTK_CSS_CHANGE_SIBLING_POSITION },
     { GTK_CSS_CHANGE_STATE, GTK_CSS_CHANGE_SIBLING_STATE },
-    { GTK_CSS_CHANGE_SOURCE, 0 }
+    { GTK_CSS_CHANGE_SOURCE, 0 },
+    { GTK_CSS_CHANGE_ANIMATE, 0 }
   };
 
   return gtk_css_change_translate (match, table, G_N_ELEMENTS (table)); 
@@ -75,6 +76,7 @@ _gtk_css_change_for_child (GtkCssChange match)
     { GTK_CSS_CHANGE_SIBLING_POSITION, GTK_CSS_CHANGE_PARENT_SIBLING_POSITION },
     { GTK_CSS_CHANGE_SIBLING_STATE, GTK_CSS_CHANGE_PARENT_SIBLING_STATE },
     { GTK_CSS_CHANGE_SOURCE, 0 },
+    { GTK_CSS_CHANGE_ANIMATE, 0 }
   };
 
   return gtk_css_change_translate (match, table, G_N_ELEMENTS (table)); 

gtk/gtkcsstypesprivate.h

@@ -43,10 +43,11 @@ typedef enum { /*< skip >*/
   GTK_CSS_CHANGE_PARENT_SIBLING_POSITION  = (1 << 14),
   GTK_CSS_CHANGE_PARENT_SIBLING_STATE     = (1 << 15),
   /* add more */
-  GTK_CSS_CHANGE_SOURCE                   = (1 << 16)
+  GTK_CSS_CHANGE_SOURCE                   = (1 << 16),
+  GTK_CSS_CHANGE_ANIMATE                  = (1 << 17)
 } GtkCssChange;
 
-#define GTK_CSS_CHANGE_ANY ((1 << 17) - 1)
+#define GTK_CSS_CHANGE_ANY ((1 << 18) - 1)
 #define GTK_CSS_CHANGE_ANY_SELF (GTK_CSS_CHANGE_CLASS | GTK_CSS_CHANGE_NAME | GTK_CSS_CHANGE_POSITION | GTK_CSS_CHANGE_STATE)
 #define GTK_CSS_CHANGE_ANY_SIBLING (GTK_CSS_CHANGE_SIBLING_CLASS | GTK_CSS_CHANGE_SIBLING_NAME | \
                                     GTK_CSS_CHANGE_SIBLING_POSITION | GTK_CSS_CHANGE_SIBLING_STATE)

gtk/gtkstylecontext.c

@@ -350,6 +350,9 @@ struct _GtkStyleContextPrivate
 
   GtkStyleCascade *cascade;
 
+  GtkStyleContext *animation_list_prev;
+  GtkStyleContext *animation_list_next;
+
   GtkStyleContext *parent;
   GSList *children;
   GtkWidget *widget;            
@@ -379,6 +382,8 @@ enum {
 };
 
 static guint signals[LAST_SIGNAL] = { 0 };
+static GtkStyleContext *_running_animations = NULL;
+guint _running_animations_timer_id = 0;
 
 static void gtk_style_context_finalize (GObject *object);
 
@@ -675,6 +680,82 @@ gtk_style_context_init (GtkStyleContext *style_context)
                                  _gtk_style_cascade_get_for_screen (priv->screen));
 }
 
+static gboolean
+gtk_style_context_do_animations (gpointer unused)
+{
+  GtkStyleContext *context;
+
+  for (context = _running_animations;
+       context != NULL;
+       context = context->priv->animation_list_next)
+    {
+      _gtk_style_context_queue_invalidate (context, GTK_CSS_CHANGE_ANIMATE);
+    }
+
+  return TRUE;
+}
+
+static gboolean
+gtk_style_context_is_animating (GtkStyleContext *context)
+{
+  GtkStyleContextPrivate *priv = context->priv;
+
+  return priv->animation_list_prev != NULL
+      || _running_animations == context;
+}
+
+static void
+gtk_style_context_stop_animating (GtkStyleContext *context)
+{
+  GtkStyleContextPrivate *priv = context->priv;
+
+  if (!gtk_style_context_is_animating (context))
+    return;
+
+  if (priv->animation_list_prev == NULL)
+    {
+      _running_animations = priv->animation_list_next;
+
+      if (_running_animations == NULL)
+        {
+          /* we were the last animation */
+          g_source_remove (_running_animations_timer_id);
+          _running_animations_timer_id = 0;
+        }
+    }
+  else
+    priv->animation_list_prev->priv->animation_list_next = priv->animation_list_next;
+
+  if (priv->animation_list_next)
+    priv->animation_list_next->priv->animation_list_prev = priv->animation_list_prev;
+
+  priv->animation_list_next = NULL;
+  priv->animation_list_prev = NULL;
+}
+
+static void G_GNUC_UNUSED
+gtk_style_context_start_animating (GtkStyleContext *context)
+{
+  GtkStyleContextPrivate *priv = context->priv;
+
+  if (gtk_style_context_is_animating (context))
+    return;
+
+  if (_running_animations == NULL)
+    {
+      _running_animations_timer_id = gdk_threads_add_timeout (25,
+                                                              gtk_style_context_do_animations,
+                                                              NULL);
+      _running_animations = context;
+    }
+  else
+    {
+      priv->animation_list_next = _running_animations;
+      _running_animations->priv->animation_list_prev = context;
+      _running_animations = context;
+    }
+}
+
 static void
 gtk_style_context_finalize (GObject *object)
 {
@@ -684,6 +765,8 @@ gtk_style_context_finalize (GObject *object)
   style_context = GTK_STYLE_CONTEXT (object);
   priv = style_context->priv;
 
+  gtk_style_context_stop_animating (style_context);
+
   /* children hold a reference to us */
   g_assert (priv->children == NULL);