[pitivi] elements: Make keyframe line visible even when at 0

[Alexandru Băluț <alexbalut src gnome org>]

commit eb424916ca7eb2cf9dfb494d89ba06f1265e475e
Author: Thibault Saunier <tsaunier gnome org>
Date:   Tue Feb 2 11:52:39 2016 +0100

    elements: Make keyframe line visible even when at 0
    
    Fixes https://phabricator.freedesktop.org/T3537
    
    Differential Revision: https://phabricator.freedesktop.org/D722

 pitivi/timeline/elements.py |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/pitivi/timeline/elements.py b/pitivi/timeline/elements.py
index 64fff35..4fd4ce6 100644
--- a/pitivi/timeline/elements.py
+++ b/pitivi/timeline/elements.py
@@ -4,6 +4,7 @@
 #       pitivi/timeline/elements.py
 #
 # Copyright (c) 2013, Mathieu Duponchelle <mduponchelle1 gmail com>
+# Copyright (c) 2016, Thibault Saunier <tsaunier gnome org>
 #
 # This program is free software; you can redistribute it and/or
 # modify it under the terms of the GNU Lesser General Public
@@ -173,8 +174,9 @@ class KeyframeCurve(FigureCanvas, Loggable):
         if height <= 0:
             return
 
+        ylim_min = -(KEYFRAME_LINE_HEIGHT / height)
         ylim_max = (self.__ylim_max * height) / (height - KEYFRAME_LINE_HEIGHT)
-        self.__ax.set_ylim(self.__ylim_min, ylim_max)
+        self.__ax.set_ylim(ylim_min, ylim_max)
 
     def __heightRequestCb(self, unused_self, unused_pspec):
         self.__computeYlim()
@@ -290,8 +292,9 @@ class KeyframeCurve(FigureCanvas, Loggable):
             if event.ydata is not None and event.xdata is not None:
                 keyframe_ts = self.__computeKeyframeNewTimestamp(event)
                 self.__source.unset(int(self.__offset))
-                self.__source.set(keyframe_ts,
-                                  min(self.__ylim_max, event.ydata))
+
+                value = max(self.__ylim_min, min(self.__ylim_max, event.ydata))
+                self.__source.set(keyframe_ts, value)
                 self.__offset = keyframe_ts
                 self.__setTooltip(event)