implemented bulk of curve editor's functionality

While certainly not entirely complete yet, this implements most of the UI
functionality of the graph editor.

app/widget/keyframeview/keyframeview.cpp

@@ -37,7 +37,8 @@ void KeyframeView::AddKeyframe(NodeKeyframePtr key, int y)
   QPoint local_pt = mapFromGlobal(global_pt);
   QPointF scene_pt = mapToScene(local_pt);
 
-  KeyframeViewItem* item = new KeyframeViewItem(key, scene_pt.y());
+  KeyframeViewItem* item = new KeyframeViewItem(key);
+  item->SetOverrideY(scene_pt.y());
   item->SetScale(scale_);
   item_map_.insert(key.get(), item);
   scene()->addItem(item);
@@ -45,7 +46,7 @@ void KeyframeView::AddKeyframe(NodeKeyframePtr key, int y)
 
 void KeyframeView::RemoveKeyframe(NodeKeyframePtr key)
 {
-  delete item_map_.value(key.get());
+  delete item_map_.take(key.get());
 }
 
 void KeyframeView::mousePressEvent(QMouseEvent *event)

app/widget/keyframeview/keyframeviewitem.cpp

@@ -7,11 +7,11 @@
 
 #include "common/qtversionabstraction.h"
 
-KeyframeViewItem::KeyframeViewItem(NodeKeyframePtr key, qreal vcenter, QGraphicsItem *parent) :
+KeyframeViewItem::KeyframeViewItem(NodeKeyframePtr key, QGraphicsItem *parent) :
   QGraphicsRectItem(parent),
   key_(key),
   scale_(1.0),
-  middle_(vcenter)
+  vert_center_(0)
 {
   keyframe_size_ = QFontMetricsWidth(qApp->fontMetrics(), "Oi");
   setFlag(QGraphicsItem::ItemIsSelectable);
@@ -24,6 +24,12 @@ KeyframeViewItem::KeyframeViewItem(NodeKeyframePtr key, qreal vcenter, QGraphics
   UpdatePos();
 }
 
+void KeyframeViewItem::SetOverrideY(qreal vertical_center)
+{
+  vert_center_ = vertical_center;
+  UpdatePos();
+}
+
 void KeyframeViewItem::SetScale(double scale)
 {
   scale_ = scale;
@@ -35,6 +41,11 @@ NodeKeyframePtr KeyframeViewItem::key() const
   return key_;
 }
 
+QPointF KeyframeViewItem::center_pos() const
+{
+  return pos() + rect().center();
+}
+
 void KeyframeViewItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
 {
   painter->setPen(Qt::black);
@@ -71,7 +82,7 @@ void KeyframeViewItem::UpdatePos()
 {
   double x_center = key_->time().toDouble() * scale_;
 
-  setPos(x_center - keyframe_size_/2, middle_ - keyframe_size_/2);
+  setPos(x_center - keyframe_size_/2, vert_center_ - keyframe_size_/2);
 }
 
 void KeyframeViewItem::Redraw()

app/widget/keyframeview/keyframeviewitem.h

@@ -9,12 +9,16 @@ class KeyframeViewItem : public QObject, public QGraphicsRectItem
 {
   Q_OBJECT
 public:
-  KeyframeViewItem(NodeKeyframePtr key, qreal vcenter, QGraphicsItem *parent = nullptr);
+  KeyframeViewItem(NodeKeyframePtr key, QGraphicsItem *parent = nullptr);
+
+  void SetOverrideY(qreal vertical_center);
 
   void SetScale(double scale);
 
   NodeKeyframePtr key() const;
 
+  QPointF center_pos() const;
+
 protected:
   virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr) override;
 
@@ -23,7 +27,7 @@ private:
 
   double scale_;
 
-  qreal middle_;
+  qreal vert_center_;
 
   int keyframe_size_;