[sysprof/wip/visualizers] visualizer-ticks: adjust ticks for capture epoch

[Christian Hergert <chergert src gnome org>]

commit c116120563c1d73da603c53aa505fa38dc802eaa
Author: Christian Hergert <chergert redhat com>
Date:   Fri Sep 30 13:21:17 2016 -0700

    visualizer-ticks: adjust ticks for capture epoch
    
    We need to take into account the real start of the capture to
    land the ticks in the right position. Add "epoch" concept
    to SpVisualizerTicks for just this purpose.

 lib/sp-visualizer-ticks.c |   43 ++++++++++++++++++++++++++++++++++++++++++-
 lib/sp-visualizer-ticks.h |    3 +++
 lib/sp-visualizer-view.c  |    2 ++
 3 files changed, 47 insertions(+), 1 deletions(-)
---
diff --git a/lib/sp-visualizer-ticks.c b/lib/sp-visualizer-ticks.c
index 586d720..f705c2a 100644
--- a/lib/sp-visualizer-ticks.c
+++ b/lib/sp-visualizer-ticks.c
@@ -27,6 +27,7 @@ struct _SpVisualizerTicks
 {
   GtkDrawingArea parent_instance;
 
+  gint64 epoch;
   gint64 begin_time;
   gint64 end_time;
 };
@@ -70,6 +71,7 @@ draw_ticks (SpVisualizerTicks *self,
 {
   gdouble half;
   gdouble space;
+  gdouble offset;
   gint64 timespan;
 
   g_assert (SP_IS_VISUALIZER_TICKS (self));
@@ -82,7 +84,13 @@ draw_ticks (SpVisualizerTicks *self,
   space = (gdouble)area->width / (gdouble)timespan * (gdouble)tick_sizing[ticks].span;
   half = tick_sizing[ticks].width / 2.0;
 
-  for (gdouble x = 0; x < area->width; x += space)
+  /* Take our epoch into account to calculate the offset of the
+   * first tick, which might not align perfectly when the beginning
+   * of the visible area.
+   */
+  offset = ((self->begin_time - self->epoch) % tick_sizing[ticks].span) / (gdouble)tick_sizing[ticks].span * 
space;
+
+  for (gdouble x = -offset; x < area->width; x += space)
     {
       cairo_move_to (cr, (gint)x - .5 - (gint)half, 0);
       cairo_line_to (cr, (gint)x - .5 - (gint)half, tick_sizing[ticks].height);
@@ -208,3 +216,36 @@ sp_visualizer_ticks_set_time_range (SpVisualizerTicks *self,
 
   gtk_widget_queue_draw (GTK_WIDGET (self));
 }
+
+gint64
+sp_visualizer_ticks_get_epoch (SpVisualizerTicks *self)
+{
+  g_return_val_if_fail (SP_IS_VISUALIZER_TICKS (self), 0);
+
+  return self->epoch;
+}
+
+/*
+ * Sets the epoch for the visualizer ticks.
+ *
+ * The epoch is the "real" starting time of the capture, where as the
+ * sp_visualizer_ticks_set_time_range() function sets the visible range
+ * of the capture.
+ *
+ * This is used to calculate the offset of the beginning of the capture
+ * from begin_time so that the ticks appear in the proper location.
+ *
+ * This function should only need to be called when the reader is changed.
+ */
+void
+sp_visualizer_ticks_set_epoch (SpVisualizerTicks *self,
+                               gint64             epoch)
+{
+  g_return_if_fail (SP_IS_VISUALIZER_TICKS (self));
+
+  if (self->epoch != epoch)
+    {
+      self->epoch = epoch;
+      gtk_widget_queue_draw (GTK_WIDGET (self));
+    }
+}
diff --git a/lib/sp-visualizer-ticks.h b/lib/sp-visualizer-ticks.h
index c75ce5e..5efeee3 100644
--- a/lib/sp-visualizer-ticks.h
+++ b/lib/sp-visualizer-ticks.h
@@ -28,6 +28,9 @@ G_BEGIN_DECLS
 G_DECLARE_FINAL_TYPE (SpVisualizerTicks, sp_visualizer_ticks, SP, VISUALIZER_TICKS, GtkDrawingArea)
 
 GtkWidget *sp_visualizer_ticks_new            (void);
+void       sp_visualizer_ticks_set_epoch      (SpVisualizerTicks *self,
+                                               gint64             epoch);
+gint64     sp_visualizer_ticks_get_epoch      (SpVisualizerTicks *self);
 void       sp_visualizer_ticks_get_time_range (SpVisualizerTicks *self,
                                                gint64            *begin_time,
                                                gint64            *end_time);
diff --git a/lib/sp-visualizer-view.c b/lib/sp-visualizer-view.c
index 26df366..b0b9565 100644
--- a/lib/sp-visualizer-view.c
+++ b/lib/sp-visualizer-view.c
@@ -328,6 +328,8 @@ sp_visualizer_view_set_reader (SpVisualizerView *self,
           begin_time = sp_capture_reader_get_start_time (reader);
           end_time = sp_capture_reader_get_end_time (reader);
 
+          sp_visualizer_ticks_set_epoch (priv->ticks, begin_time);
+
           g_object_set (priv->scroll_adjustment,
                         "lower", (gdouble)begin_time,
                         "upper", (gdouble)end_time,