viewer: set automatic divider on connection

Probably not a permanent solution, but will aid performance for the
time-being.

app/common/power.h

@@ -0,0 +1,56 @@
+/***
+
+  Olive - Non-Linear Video Editor
+  Copyright (C) 2019 Olive Team
+
+  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 POWER_H
+#define POWER_H
+
+#include <stdint.h>
+
+#include "common/define.h"
+
+OLIVE_NAMESPACE_ENTER
+
+uint32_t ceil_to_power_of_2(uint32_t v)
+{
+  v--;
+  v |= v >> 1;
+  v |= v >> 2;
+  v |= v >> 4;
+  v |= v >> 8;
+  v |= v >> 16;
+  v++;
+
+  return v;
+}
+
+uint32_t floor_to_power_of_2(uint32_t x)
+{
+  x = x | (x >> 1);
+  x = x | (x >> 2);
+  x = x | (x >> 4);
+  x = x | (x >> 8);
+  x = x | (x >> 16);
+
+  return x - (x >> 1);
+}
+
+OLIVE_NAMESPACE_EXIT
+
+#endif // POWER_H

app/config/config.cpp

@@ -77,7 +77,7 @@ void Config::SetDefaults()
   config_map_["AutoscaleByDefault"] = false;
   config_map_["Autoscroll"] = AutoScroll::kPage;
   config_map_["DefaultViewerDivider"] = 2;
-  config_map_["AutoSelectDivider"] = false;
+  config_map_["AutoSelectDivider"] = true;
   config_map_["SetNameWithMarker"] = false;
   config_map_["RectifiedWaveforms"] = false;
   config_map_["DropWithoutSequenceBehavior"] = TimelineWidget::kDWSAsk;

app/widget/viewer/viewer.cpp

@@ -31,6 +31,7 @@
 #include <QVBoxLayout>
 
 #include "audio/audiomanager.h"
+#include "common/power.h"
 #include "common/timecodefunctions.h"
 #include "config/config.h"
 #include "project/item/sequence/sequence.h"
@@ -558,7 +559,7 @@ int ViewerWidget::CalculateDivider()
     int long_side_of_video = qMax(GetConnectedNode()->video_params().width(), GetConnectedNode()->video_params().height());
     int long_side_of_widget = qMax(display_widget_->width(), display_widget_->height());
 
-    return qMax(1, long_side_of_video / long_side_of_widget);
+    return ceil_to_power_of_2(qMax(1, long_side_of_video / long_side_of_widget));
   }
 
   return divider_;