DagLib 1.0.1

DagLib

A generic DAG (directed acyclic graph) library for .NET, built around Guid-based node identity with cycle detection, topological sorting, and ancestor/descendant traversal baked in. It's designed to sit behind immediate-mode node editor UIs like ImNodes, but has no dependency on any UI library itself.

Why

Node editors need a graph model that's easy to mutate interactively — add a node here, drag a link there — while never letting the underlying structure become invalid. DagLib rejects edges that would create a cycle at the moment you try to add them, so the UI layer never has to deal with an inconsistent graph in the first place. A full-graph cycle scan is also available for the one case interactive checks can't cover: data coming in from an external source, like a save file.

Features

• Typed payloads — Node<T> and DagGraph<T> let each node carry any data type: a label, a record with position and color, a delegate, whatever the application needs.
• Two layers of cycle safety — a cheap, single-edge check (WouldCreateCycle) for interactive use, and a full-graph sweep (HasCycle) for validating data loaded from elsewhere.
• Topological sort via Kahn's algorithm.
• Traversal helpers — GetAncestors and GetDescendants for impact analysis ("what does this feed into?" / "what feeds into this?").
• ID bridging — NodeIdMapper maps each node's persistent Guid to a throwaway int for int-keyed APIs like ImNodes, without ever discarding the original identity.
• ImNodes-facing helper — ImNodesGraphView<T> combines a DagGraph<T> and a NodeIdMapper into a single facade for wiring up ImNodes events by int ID, so glue code isn't duplicated at every call site.
• JSON persistence — DagLib.Serialization.GraphSerializer saves and loads graphs as JSON, encoding edges as array indices rather than repeated Guids to keep files small, with an optional GZip-compressed format for larger graphs.

Install

dotnet add package DagLib

Usage

using DagLib;

var graph = new DagGraph<string>();
var a = graph.AddNode("A");
var b = graph.AddNode("B");
var c = graph.AddNode("C");

graph.AddEdge(a, b);
graph.AddEdge(a, c);

var order = graph.TopologicalSort();

Saving and loading JSON

using DagLib.Serialization;

GraphSerializer.Save(graph, "graph.json");
GraphSerializer.Save(graph, "graph.json.gz", compress: true);

var loaded = GraphSerializer.Load<string>("graph.json");

Working with ImNodes

using DagLib;

var mapper = new NodeIdMapper();
int imNodesId = mapper.GetOrCreateImNodesId(a.Id);
// pass imNodesId into the native API, e.g. ImNodes.BeginNode(imNodesId);

For a tighter integration, ImNodesGraphView<T> wraps a DagGraph<T> and a NodeIdMapper together, so ImNodes event handlers can work directly with int IDs instead of manually translating back and forth:

using DagLib;

var view = new ImNodesGraphView<string>(graph, mapper);

// Handling an IsLinkCreated event
view.AddEdge(fromImNodesId, toImNodesId);

// Handling a node deletion — removes it from both the graph and the ID mapping
view.RemoveNode(imNodesId);

// Driving a render loop
foreach (var (node, id) in view.GetRenderableNodes())
{
    ImNodes.BeginNode(id);
    // ... build UI from node.Data ...
    ImNodes.EndNode();
}

License

MIT