automatically store block connections in the transitionblock class

Convenience code that automatically returns valid blocks if they're connected.

app/node/block/transition/transition.cpp

@@ -6,10 +6,14 @@ TransitionBlock::TransitionBlock() :
 {
   out_block_input_ = new NodeInput("out_block_in", NodeParam::kBuffer);
   out_block_input_->set_is_keyframable(false);
+  connect(out_block_input_, &NodeParam::EdgeAdded, this, &TransitionBlock::BlockConnected);
+  connect(out_block_input_, &NodeParam::EdgeRemoved, this, &TransitionBlock::BlockDisconnected);
   AddInput(out_block_input_);
 
   in_block_input_ = new NodeInput("in_block_in", NodeParam::kBuffer);
   in_block_input_->set_is_keyframable(false);
+  connect(in_block_input_, &NodeParam::EdgeAdded, this, &TransitionBlock::BlockConnected);
+  connect(in_block_input_, &NodeParam::EdgeRemoved, this, &TransitionBlock::BlockDisconnected);
   AddInput(in_block_input_);
 }
 
@@ -43,3 +47,27 @@ rational TransitionBlock::out_offset() const
 {
   return 0;
 }
+
+void TransitionBlock::BlockConnected(NodeEdgePtr edge)
+{
+  if (!edge->output()->parentNode()->IsBlock()) {
+    return;
+  }
+
+  Block* block = static_cast<Block*>(edge->output()->parentNode());
+
+  if (edge->input() == out_block_input_) {
+    connected_out_block_ = block;
+  } else {
+    connected_in_block_ = block;
+  }
+}
+
+void TransitionBlock::BlockDisconnected(NodeEdgePtr edge)
+{
+  if (edge->input() == out_block_input_) {
+    connected_out_block_ = nullptr;
+  } else {
+    connected_in_block_ = nullptr;
+  }
+}

app/node/block/transition/transition.h

@@ -18,6 +18,9 @@ public:
   rational in_offset() const;
   rational out_offset() const;
 
+  Block* connected_out_block() const;
+  Block* connected_in_block() const;
+
 private:
   NodeInput* out_block_input_;
 
@@ -27,6 +30,11 @@ private:
 
   Block* connected_in_block_;
 
+private slots:
+  void BlockConnected(NodeEdgePtr edge);
+
+  void BlockDisconnected(NodeEdgePtr edge);
+
 };
 
 #endif // TRANSITIONBLOCK_H