started base transition type

Like the base "Block" type, the "Transition" type will not be a node used on its
own, it will have to be derived. This type defines some basic behavior for a
transition (e.g. how much it overlaps its "from" and "to" blocks).

app/node/block/CMakeLists.txt

@@ -16,6 +16,7 @@
 
 add_subdirectory(clip)
 add_subdirectory(gap)
+add_subdirectory(transition)
 
 set(OLIVE_SOURCES
   ${OLIVE_SOURCES}

app/node/block/block.h

@@ -42,7 +42,8 @@ public:
   enum Type {
     kClip,
     kGap,
-    kTrack
+    kTrack,
+    kTransition
   };
 
   virtual Type type() const = 0;
@@ -54,9 +55,9 @@ public:
   void set_in(const rational& in);
   void set_out(const rational& out);
 
-  const rational &length() const;
-  void set_length(const rational &length);
-  void set_length_and_media_in(const rational &length);
+  const rational& length() const;
+  virtual void set_length(const rational &length);
+  virtual void set_length_and_media_in(const rational &length);
 
   Block* previous();
   Block* next();

app/node/block/transition/CMakeLists.txt

@@ -0,0 +1,22 @@
+# 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/>.
+
+set(OLIVE_SOURCES
+  ${OLIVE_SOURCES}
+  node/block/transition/transition.h
+  node/block/transition/transition.cpp
+  PARENT_SCOPE
+)

app/node/block/transition/transition.cpp

@@ -0,0 +1,62 @@
+#include "transition.h"
+
+TransitionBlock::TransitionBlock()
+{
+  out_block_input_ = new NodeInput("out_block_in");
+  AddInput(out_block_input_);
+
+  in_block_input_ = new NodeInput("in_block_in");
+  AddInput(in_block_input_);
+}
+
+Block::Type TransitionBlock::type() const
+{
+  return kTransition;
+}
+
+NodeInput *TransitionBlock::out_block_input() const
+{
+  return out_block_input_;
+}
+
+NodeInput *TransitionBlock::in_block_input() const
+{
+  return in_block_input_;
+}
+
+void TransitionBlock::Retranslate()
+{
+  out_block_input_->set_name(tr("From"));
+  in_block_input_->set_name(tr("To"));
+}
+
+void TransitionBlock::set_length(const rational &length)
+{
+  Q_UNUSED(length)
+  qCritical() << "Set length is not permitted on a transition";
+  abort();
+}
+
+void TransitionBlock::set_length_and_media_in(const rational &length)
+{
+  Q_UNUSED(length)
+  qCritical() << "Set length and media in is not permitted on a transition";
+  abort();
+}
+
+void TransitionBlock::set_in_offset(const rational &in_offset)
+{
+  in_offset_ = in_offset;
+  RecalculateLength();
+}
+
+void TransitionBlock::set_out_offset(const rational &out_offset)
+{
+  out_offset_ = out_offset;
+  RecalculateLength();
+}
+
+void TransitionBlock::RecalculateLength()
+{
+  Block::set_length(in_offset_ + out_offset_);
+}

app/node/block/transition/transition.h

@@ -0,0 +1,38 @@
+#ifndef TRANSITIONBLOCK_H
+#define TRANSITIONBLOCK_H
+
+#include "node/block/block.h"
+
+class TransitionBlock : public Block
+{
+public:
+  TransitionBlock();
+
+  virtual Type type() const override;
+
+  NodeInput* out_block_input() const;
+
+  NodeInput* in_block_input() const;
+
+  virtual void Retranslate() override;
+
+  virtual void set_length(const rational &length) override;
+  virtual void set_length_and_media_in(const rational &length) override;
+
+  void set_in_offset(const rational& in_offset);
+  void set_out_offset(const rational& out_offset);
+
+private:
+  void RecalculateLength();
+
+  NodeInput* out_block_input_;
+
+  NodeInput* in_block_input_;
+
+  rational in_offset_;
+
+  rational out_offset_;
+
+};
+
+#endif // TRANSITIONBLOCK_H

app/widget/timelinewidget/timelinewidget.cpp

@@ -573,6 +573,7 @@ void TimelineWidget::AddBlock(Block *block, TrackReference track)
 {
   switch (block->type()) {
   case Block::kClip:
+  case Block::kTransition:
   case Block::kGap:
   {
     TimelineViewBlockItem* item = new TimelineViewBlockItem();

app/widget/timelinewidget/view/timelineviewblockitem.cpp

@@ -79,6 +79,7 @@ void TimelineViewBlockItem::paint(QPainter *painter, const QStyleOptionGraphicsI
 
   switch (block_->type()) {
   case Block::kClip:
+  case Block::kTransition: // FIXME: Temporary, the transition should have its own UI representation at some point
     /*QLinearGradient grad;
     grad.setStart(0, rect().top());
     grad.setFinalStop(0, rect().bottom());