visualizer-ticks: start on minimal ticks implementation

We need some sort of scale for content, so we will do this with
an overlay for now. However, we will also want something to be
able to do selections in the future.

This still needs some iteration for correctness, but this sort
of gets the ball rolling.

lib/sp-visualizer-ticks.h

@@ -0,0 +1,40 @@
+/* sp-visualizer-ticks.h
+ *
+ * Copyright (C) 2016 Christian Hergert <chergert@redhat.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef SP_VISUALIZER_TICKS_H
+#define SP_VISUALIZER_TICKS_H
+
+#include <gtk/gtk.h>
+
+G_BEGIN_DECLS
+
+#define SP_TYPE_VISUALIZER_TICKS (sp_visualizer_ticks_get_type())
+
+G_DECLARE_FINAL_TYPE (SpVisualizerTicks, sp_visualizer_ticks, SP, VISUALIZER_TICKS, GtkDrawingArea)
+
+GtkWidget *sp_visualizer_ticks_new            (void);
+void       sp_visualizer_ticks_get_time_range (SpVisualizerTicks *self,
+                                               gint64            *begin_time,
+                                               gint64            *end_time);
+void       sp_visualizer_ticks_set_time_range (SpVisualizerTicks *self,
+                                               gint64             begin_time,
+                                               gint64             end_time);
+
+G_END_DECLS
+
+#endif /* SP_VISUALIZER_TICKS_H */