node: split off traversing functions from renderer for usage elsewhere

Fixes issue where Viewer node wouldn't pick up correct length if a tracks
weren't in use.

app/node/traverser.cpp

@@ -0,0 +1,76 @@
+#include "traverser.h"
+
+#include "node.h"
+
+NodeTraverser::NodeTraverser()
+{
+
+}
+
+NodeValueDatabase NodeTraverser::GenerateDatabase(const Node* node, const TimeRange &range)
+{
+  NodeValueDatabase database;
+
+  // We need to insert tables into the database for each input
+  foreach (NodeParam* param, node->parameters()) {
+    if (IsCancelled()) {
+      return NodeValueDatabase();
+    }
+
+    if (param->type() == NodeParam::kInput) {
+      NodeInput* input = static_cast<NodeInput*>(param);
+      TimeRange input_time = node->InputTimeAdjustment(input, range);
+
+      NodeValueTable table = ProcessInput(input, input_time);
+
+      InputProcessingEvent(input, input_time, &table);
+
+      database.Insert(input, table);
+    }
+  }
+
+  return database;
+}
+
+NodeValueTable NodeTraverser::ProcessNode(const NodeDependency& dep)
+{
+  const Node* node = dep.node();
+
+  if (node->IsTrack()) {
+    // If the range is not wholly contained in this Block, we'll need to do some extra processing
+    return RenderBlock(static_cast<const TrackOutput*>(node), dep.range());
+  }
+
+  // FIXME: Cache certain values here if we've already processed them before
+
+  // Generate database of input values of node
+  NodeValueDatabase database = GenerateDatabase(node, dep.range());
+
+  // By this point, the node should have all the inputs it needs to render correctly
+  NodeValueTable table = node->Value(database);
+
+  ProcessNodeEvent(node, dep.range(), database, &table);
+
+  return table;
+}
+
+NodeValueTable NodeTraverser::RenderBlock(const TrackOutput *track, const TimeRange &range)
+{
+  // By default, don't bother traversing blocks
+  return NodeValueTable();
+}
+
+NodeValueTable NodeTraverser::ProcessInput(const NodeInput *input, const TimeRange& range)
+{
+  if (input->IsConnected()) {
+    // Value will equal something from the connected node, follow it
+    return ProcessNode(NodeDependency(input->get_connected_node(), range));
+  } else {
+    // Push onto the table the value at this time from the input
+    QVariant input_value = input->get_value_at_time(range.in());
+
+    NodeValueTable table;
+    table.Push(input->data_type(), input_value);
+    return table;
+  }
+}