[pitivi] timeline: Move scroll logic closer to where it's used

[Alexandru Băluț <alexbalut src gnome org>]

commit d5aac3a98eb3e8012d165763fcfdd41a03981aaa
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Wed Oct 12 16:27:17 2016 +0200

    timeline: Move scroll logic closer to where it's used
    
    Removed some methods in the process.
    
    Reviewed-by: Thibault Saunier <tsaunier gnome org>
    Differential Revision: https://phabricator.freedesktop.org/D1382

 pitivi/timeline/timeline.py |   44 ++++++++++++++++++++++--------------------
 1 files changed, 23 insertions(+), 21 deletions(-)
---
diff --git a/pitivi/timeline/timeline.py b/pitivi/timeline/timeline.py
index 5c086e7..212d4f2 100644
--- a/pitivi/timeline/timeline.py
+++ b/pitivi/timeline/timeline.py
@@ -549,13 +549,16 @@ class Timeline(Gtk.EventBox, Zoomable, Loggable):
         x, y = event_widget.translate_coordinates(self, event.x, event.y)
         if event.get_state() & Gdk.ModifierType.SHIFT_MASK:
             if delta_y > 0:
-                self.parent.scroll_down()
+                # Scroll down.
+                self.__scroll_adjustment(self.vadj, 1)
             elif delta_y < 0:
-                self.parent.scroll_up()
+                # Scroll up.
+                self.__scroll_adjustment(self.vadj, -1)
         elif event.get_state() & (Gdk.ModifierType.CONTROL_MASK |
                                   Gdk.ModifierType.MOD1_MASK):
+            # Zoom.
             x -= self.controls_width
-            # Figure out first where to scroll at the end
+            # Figure out first where to scroll at the end.
             if event.get_state() & Gdk.ModifierType.CONTROL_MASK:
                 # The time at the mouse cursor.
                 position = self.pixelToNs(x + self.hadj.get_value())
@@ -573,12 +576,27 @@ class Timeline(Gtk.EventBox, Zoomable, Loggable):
                 self.hadj.set_value(self.nsToPixel(position) - x)
         else:
             if delta_y > 0:
-                self.parent.scroll_right()
+                # Scroll right.
+                self.__scroll_adjustment(self.hadj, 1)
             else:
-                self.parent.scroll_left()
+                # Scroll left.
+                self.__scroll_adjustment(self.hadj, -1)
 
         return False
 
+    def __scroll_adjustment(self, adj, factor):
+        """Changes the adjustment's value depending on the page size.
+
+        The delta is the page_size of adj to the power of 2/3, for example:
+        f(200) = 34, f(600) = 71, f(1000) = 100.
+
+        Args:
+            adj (Gtk.Adjustment): The adjustment to be changed.
+            factor (int): Factor applied to the delta. -1 to scroll up/left,
+                1 to scroll down/right.
+        """
+        adj.set_value(adj.get_value() + factor * adj.props.page_size ** (2 / 3))
+
     def get_sources_at_position(self, position):
         """Gets video sources at the current position on all layers.
 
@@ -1504,22 +1522,6 @@ class TimelineContainer(Gtk.Grid, Zoomable, Loggable):
         self.log("Setting 'zoomed_fitted' to True")
         self.zoomed_fitted = True
 
-    def scroll_left(self):
-        hadj = self.timeline.hadj
-        hadj.set_value(hadj.get_value() - hadj.props.page_size ** (2 / 3))
-
-    def scroll_right(self):
-        hadj = self.timeline.hadj
-        hadj.set_value(hadj.get_value() + hadj.props.page_size ** (2 / 3))
-
-    def scroll_up(self):
-        vadj = self.timeline.vadj
-        vadj.set_value(vadj.get_value() - vadj.props.page_size ** (2 / 3))
-
-    def scroll_down(self):
-        vadj = self.timeline.vadj
-        vadj.set_value(vadj.get_value() + vadj.props.page_size ** (2 / 3))
-
     def _scrollToPixel(self, x):
         hadj = self.timeline.hadj
         self.log("Scroll to: %s %s %s", x, hadj.props.lower, hadj.props.upper)