interval: Add variadic arguments for initial/final setters

As a convenience for the C API.

Language bindings should already be using the GValue variants.

This commit also moves the custom progress functions out of the
clutter-interval.c, as they are meant to be generic interpolation
functions and not ClutterInterval-specific.

clutter/clutter-util.c

@@ -37,6 +37,7 @@
 #include <glib/gi18n-lib.h>
 
 #include "clutter-main.h"
+#include "clutter-interval.h"
 #include "clutter-private.h"
 
 #include "deprecated/clutter-util.h"
@@ -180,3 +181,150 @@ _clutter_util_rectangle_union (const cairo_rectangle_int_t *src1,
   dest->x = dest_x;
   dest->y = dest_y;
 }
+
+typedef struct
+{
+  GType value_type;
+  ClutterProgressFunc func;
+} ProgressData;
+
+G_LOCK_DEFINE_STATIC (progress_funcs);
+static GHashTable *progress_funcs = NULL;
+
+gboolean
+_clutter_has_progress_function (GType gtype)
+{
+  const char *type_name = g_type_name (gtype);
+
+  if (progress_funcs == NULL)
+    return FALSE;
+
+  return g_hash_table_lookup (progress_funcs, type_name) != NULL;
+}
+
+gboolean
+_clutter_run_progress_function (GType gtype,
+                                const GValue *initial,
+                                const GValue *final,
+                                gdouble progress,
+                                GValue *retval)
+{
+  ProgressData *pdata;
+  gboolean res;
+
+  G_LOCK (progress_funcs);
+
+  if (G_UNLIKELY (progress_funcs == NULL))
+    {
+      res = FALSE;
+      goto out;
+    }
+
+  pdata = g_hash_table_lookup (progress_funcs, g_type_name (gtype));
+  if (G_UNLIKELY (pdata == NULL))
+    {
+      res = FALSE;
+      goto out;
+    }
+
+  res = pdata->func (initial, final, progress, retval);
+
+out:
+  G_UNLOCK (progress_funcs);
+
+  return res;
+}
+
+static void
+progress_data_destroy (gpointer data_)
+{
+  g_slice_free (ProgressData, data_);
+}
+
+/**
+ * clutter_interval_register_progress_func: (skip)
+ * @value_type: a #GType
+ * @func: a #ClutterProgressFunc, or %NULL to unset a previously
+ *   set progress function
+ *
+ * Sets the progress function for a given @value_type, like:
+ *
+ * |[
+ *   clutter_interval_register_progress_func (MY_TYPE_FOO,
+ *                                            my_foo_progress);
+ * ]|
+ *
+ * Whenever a #ClutterInterval instance using the default
+ * #ClutterInterval::compute_value implementation is set as an
+ * interval between two #GValue of type @value_type, it will call
+ * @func to establish the value depending on the given progress,
+ * for instance:
+ *
+ * |[
+ *   static gboolean
+ *   my_int_progress (const GValue *a,
+ *                    const GValue *b,
+ *                    gdouble       progress,
+ *                    GValue       *retval)
+ *   {
+ *     gint ia = g_value_get_int (a);
+ *     gint ib = g_value_get_int (b);
+ *     gint res = factor * (ib - ia) + ia;
+ *
+ *     g_value_set_int (retval, res);
+ *
+ *     return TRUE;
+ *   }
+ *
+ *   clutter_interval_register_progress_func (G_TYPE_INT, my_int_progress);
+ * ]|
+ *
+ * To unset a previously set progress function of a #GType, pass %NULL
+ * for @func.
+ *
+ * Since: 1.0
+ */
+void
+clutter_interval_register_progress_func (GType               value_type,
+                                         ClutterProgressFunc func)
+{
+  ProgressData *progress_func;
+  const char *type_name;
+
+  g_return_if_fail (value_type != G_TYPE_INVALID);
+
+  type_name = g_type_name (value_type);
+
+  G_LOCK (progress_funcs);
+
+  if (G_UNLIKELY (progress_funcs == NULL))
+    progress_funcs = g_hash_table_new_full (NULL, NULL,
+                                            NULL,
+                                            progress_data_destroy);
+
+  progress_func =
+    g_hash_table_lookup (progress_funcs, type_name);
+
+  if (G_UNLIKELY (progress_func))
+    {
+      if (func == NULL)
+        {
+          g_hash_table_remove (progress_funcs, type_name);
+          g_slice_free (ProgressData, progress_func);
+        }
+      else
+        progress_func->func = func;
+    }
+  else
+    {
+      progress_func = g_slice_new (ProgressData);
+      progress_func->value_type = value_type;
+      progress_func->func = func;
+
+      g_hash_table_replace (progress_funcs,
+                            (gpointer) type_name,
+                            progress_func);
+    }
+
+  G_UNLOCK (progress_funcs);
+}