began UI for keyframing

Largely extending the existing NodeParamView with functionality from the
previous release.

app/widget/keyframeview/keyframeviewitem.cpp

@@ -0,0 +1,83 @@
+#include "keyframeviewitem.h"
+
+#include <QApplication>
+#include <QPainter>
+#include <QStyleOptionGraphicsItem>
+#include <QWidget>
+
+#include "common/qtversionabstraction.h"
+
+KeyframeViewItem::KeyframeViewItem(QGraphicsItem *parent) :
+  QGraphicsRectItem(parent),
+  key_(nullptr),
+  scale_(1.0)
+{
+  keyframe_size_ = QFontMetricsWidth(qApp->fontMetrics(), "Oi");
+  setFlag(QGraphicsItem::ItemIsSelectable);
+  setFlag(QGraphicsItem::ItemIsMovable);
+}
+
+void KeyframeViewItem::SetKeyframe(NodeKeyframe *key)
+{
+  key_ = key;
+  UpdateRect();
+}
+
+void KeyframeViewItem::SetVerticalCenter(int middle)
+{
+  middle_ = middle;
+  UpdateRect();
+}
+
+void KeyframeViewItem::SetScale(double scale)
+{
+  scale_ = scale;
+  UpdateRect();
+}
+
+void KeyframeViewItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
+{
+  if (!key_) {
+    return;
+  }
+
+  painter->setPen(Qt::black);
+
+  if (option->state & QStyle::State_Selected) {
+    painter->setBrush(widget->palette().highlight());
+  } else {
+    painter->setBrush(widget->palette().text());
+  }
+
+  switch (key_->type()) {
+  case NodeKeyframe::kLinear:
+  {
+    QPointF points[] = {
+      QPointF(rect().center().x(), rect().top()),
+      QPointF(rect().right(), rect().center().y()),
+      QPointF(rect().center().x(), rect().bottom()),
+      QPointF(rect().left(), rect().center().y())
+    };
+
+    painter->drawPolygon(points, 4);
+    break;
+  }
+  case NodeKeyframe::kBezier:
+    painter->drawEllipse(rect());
+    break;
+  case NodeKeyframe::kHold:
+    painter->drawRect(rect());
+    break;
+  }
+}
+
+void KeyframeViewItem::UpdateRect()
+{
+  if (!key_) {
+    return;
+  }
+
+  double x_center = key_->time().toDouble() * scale_;
+
+  setRect(x_center - keyframe_size_/2, middle_ - keyframe_size_/2, keyframe_size_, keyframe_size_);
+}