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Building and Drawing a Graph in Unity using Gizmos

 ·   ·  ☕ 2 min read

    Unity’s Gizmos can be a really powerful way to debug your objects and relationships. In this video we’re going to be focusing on drawing a graph, a set of nodes and edges with unique characteristics. We’re going to be making a graph which can store nodes with a position and color as well as edges which store a weight and color. With OnDrawGizmos we’ll draw both of these so we can actually see what’s happening.

    The graph we’ll be creating in this video is a directed graph - a digraph. This means that edges in the graph are directed and represent a single connection from one node to another. Think of this like how a city might have one-way streets. We can limit and control our graphs relationships more closely this way.

    To make our graph a bit more accommodating to a number of unique uses we’ll be creating the graph using generic types. This will allow our edges and nodes to both store unique data. We can use this to store positioned nodes with weighted edges as you might want to do for pathfinding. Another solution might be to have your nodes store pieces of a technology tree and your edges store the requirements to unlock those nodes.

    To draw our graph we can use the following code:

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    void OnDrawGizmos() {
        // If a graph does not exist, generate one in Start()
        if (graph == null) { 
            Start();
        }
    
        // draw all the graphs nodes
        foreach(var node in graph.Nodes) {
            Gizmos.color = node.NodeColor;
            Gizmos.DrawSphere(node.Value, 0.125f);
        }
    
        // draw all the edges of the graph
        foreach(var edge in graph.Edges) {
            Gizmos.color = edge.EdgeColor;
            Gizmos.DrawLine(edge.From.Value, edge.To.Value);
        }
    }
    

    Sam Wronski
    WRITTEN BY
    Sam Wronski
    Maker of things, currently helping build cloud things @ Google. World of Zero is a personal project disconnected from my professional work. Lets make something awesome together!