make nodes more const friendly and prepare their functions for stateless work

Since the nodes won't be holding any rendering data themselves in this system,
we may as well enforce some level of non-write access by setting all the
functions to const. They were already const-friendly, they just weren't
labelled as such.

app/node/output/track/track.cpp

@@ -37,7 +37,6 @@ TrackOutput::TrackOutput() :
   connect(block_input_, SIGNAL(SizeChanged(int)), this, SLOT(BlockListSizeChanged(int)));
 
   track_input_ = new NodeInput("track_in");
-  track_input_->set_data_type(NodeParam::kTrack);
   track_input_->set_dependent(false);
   AddParameter(track_input_);
 
@@ -55,32 +54,32 @@ const TrackType& TrackOutput::track_type()
   return track_type_;
 }
 
-Block::Type TrackOutput::type()
+Block::Type TrackOutput::type() const
 {
   return kTrack;
 }
 
-Block *TrackOutput::copy()
+Block *TrackOutput::copy() const
 {
   return new TrackOutput();
 }
 
-QString TrackOutput::Name()
+QString TrackOutput::Name() const
 {
   return tr("Track");
 }
 
-QString TrackOutput::id()
+QString TrackOutput::id() const
 {
   return "org.olivevideoeditor.Olive.track";
 }
 
-QString TrackOutput::Category()
+QString TrackOutput::Category() const
 {
   return tr("Output");
 }
 
-QString TrackOutput::Description()
+QString TrackOutput::Description() const
 {
   return tr("Node for representing and processing a single array of Blocks sorted by time. Also represents the end of "
             "a Sequence.");
@@ -98,7 +97,8 @@ void TrackOutput::SetIndex(const int &index)
 
 TrackOutput *TrackOutput::next_track()
 {
-  return ValueToPtr<TrackOutput>(track_input_->get_realtime_value_of_connected_output());
+  // FIXME: Re-do this without dynamic_cast at some point
+  return dynamic_cast<TrackOutput*>(track_input_->get_connected_node());
 }
 
 NodeInput *TrackOutput::track_input()
@@ -111,7 +111,7 @@ NodeOutput* TrackOutput::track_output()
   return track_output_;
 }
 
-Block *TrackOutput::BlockContainingTime(const rational &time)
+Block *TrackOutput::BlockContainingTime(const rational &time) const
 {
   foreach (Block* block, block_cache_) {
     if (block->in() < time && block->out() > time) {
@@ -124,7 +124,7 @@ Block *TrackOutput::BlockContainingTime(const rational &time)
   return nullptr;
 }
 
-Block *TrackOutput::NearestBlockBefore(const rational &time)
+Block *TrackOutput::NearestBlockBefore(const rational &time) const
 {
   foreach (Block* block, block_cache_) {
     // Blocks are sorted by time, so the first Block who's out point is at/after this time is the correct Block
@@ -133,10 +133,10 @@ Block *TrackOutput::NearestBlockBefore(const rational &time)
     }
   }
 
-  return this;
+  return nullptr;
 }
 
-Block *TrackOutput::NearestBlockAfter(const rational &time)
+Block *TrackOutput::NearestBlockAfter(const rational &time) const
 {
   foreach (Block* block, block_cache_) {
     // Blocks are sorted by time, so the first Block after this time is the correct Block
@@ -145,10 +145,10 @@ Block *TrackOutput::NearestBlockAfter(const rational &time)
     }
   }
 
-  return this;
+  return nullptr;
 }
 
-const QVector<Block *> &TrackOutput::Blocks()
+const QVector<Block *> &TrackOutput::Blocks() const
 {
   return block_cache_;
 }
@@ -163,17 +163,6 @@ void TrackOutput::InvalidateCache(const rational &start_range, const rational &e
   Node::InvalidateCache(start_range, end_range, from);
 }
 
-QVariant TrackOutput::Value(NodeOutput *output)
-{
-  if (output == track_output_) {
-    // Set track output correctly
-    return PtrToValue(this);
-  }
-
-  // Run default node processing
-  return Block::Value(output);
-}
-
 void TrackOutput::InsertBlockBefore(Block* block, Block* after)
 {
   InsertBlockAtIndex(block, block_cache_.indexOf(after));
@@ -301,12 +290,12 @@ TrackOutput *TrackOutput::TrackFromBlock(Block *block)
   return nullptr;
 }
 
-const rational &TrackOutput::track_length()
+const rational &TrackOutput::track_length() const
 {
   return track_length_;
 }
 
-bool TrackOutput::IsTrack()
+bool TrackOutput::IsTrack() const
 {
   return true;
 }