/// <summary>
/// Add a ConnectionGene to the builder, but only if the connection is not already present (as determined by it's neuron ID endpoints).
/// </summary>
/// <param name="connectionGene">The connection to add.</param>
/// <param name="parentGenome">The connection's parent genome. This is used to obtain NeuronGene(s) for the connection endpoints.</param>
/// <param name="overwriteExisting">A flag that indicates if this connection should take precedence over an existing connection with
/// the same endpoints.</param>
public void TryAddGene(ConnectionGene connectionGene, NeatGenome parentGenome, bool overwriteExisting)
{
// Check if a matching gene has already been added.
ConnectionEndpointsStruct connectionKey = new ConnectionEndpointsStruct(connectionGene.SourceNodeId, connectionGene.TargetNodeId);
ConnectionGene existingConnectionGene;
if (!_connectionGeneDictionary.TryGetValue(connectionKey, out existingConnectionGene))
{ // Add new connection gene.
ConnectionGene connectionGeneCopy = new ConnectionGene(connectionGene);
_connectionGeneDictionary.Add(connectionKey, connectionGeneCopy);
// Insert connection gene into a list. Use more efficient approach (append to end) if we know the gene belongs at the end.
if (connectionGeneCopy.InnovationId > _highestConnectionGeneId)
{
_connectionGeneList.Add(connectionGeneCopy);
_highestConnectionGeneId = connectionGeneCopy.InnovationId;
}
else
{
_connectionGeneList.InsertIntoPosition(connectionGeneCopy);
}
// Add neuron genes (if not already added).
// Source neuron.
NeuronGene srcNeuronGene;
if (!_neuronDictionary.TryGetValue(connectionGene.SourceNodeId, out srcNeuronGene))
{
srcNeuronGene = parentGenome.NeuronGeneList.GetNeuronById(connectionGene.SourceNodeId);
srcNeuronGene = new NeuronGene(srcNeuronGene, false); // Make a copy.
_neuronDictionary.Add(srcNeuronGene.Id, srcNeuronGene);
}
// Target neuron.
NeuronGene tgtNeuronGene;
if (!_neuronDictionary.TryGetValue(connectionGene.TargetNodeId, out tgtNeuronGene))
{
tgtNeuronGene = parentGenome.NeuronGeneList.GetNeuronById(connectionGene.TargetNodeId);
tgtNeuronGene = new NeuronGene(tgtNeuronGene, false); // Make a copy.
_neuronDictionary.Add(tgtNeuronGene.Id, tgtNeuronGene);
}
// Register connectivity with each neuron.
srcNeuronGene.TargetNeurons.Add(tgtNeuronGene.Id);
tgtNeuronGene.SourceNeurons.Add(srcNeuronGene.Id);
}
else if (overwriteExisting)
{ // The genome we are building already has a connection with the same neuron endpoints as the one we are
// trying to add. It didn't match up during correlation because it has a different innovation number, this
// is possible because the innovation history buffers throw away old innovations in a FIFO manner in order
// to prevent them from bloating.
// Here the 'overwriteExisting' flag is set so the gene we are currently trying to add is probably from the
// fitter parent, and therefore we want to use its connection weight in place of the existing gene's weight.
existingConnectionGene.Weight = connectionGene.Weight;
}
}
