How-To: Customizing Visualizations

Mix.install([
  {:yog_ex, "~> 0.98"},
  {:kino_vizjs, "~> 0.8.0"}
])

Introduction

Visualizing a graph is often the first step in debugging or communicating a complex algorithm. Yog provides powerful Yog.Render.DOT and Yog.Render.Mermaid engines that transform your graphs into visual diagrams.

Graphviz DOT Styling

Basic Styling

Control the overall look with the options map:

g = Yog.Generator.Classic.petersen()

# Change layout direction, background, and node shape
dot = Yog.Render.DOT.to_dot(g,
  Yog.Render.DOT.default_options()
  |> Map.put(:rankdir, :lr)
  |> Map.put(:bgcolor, "#f8fafc")
  |> Map.put(:node_shape, :doublecircle)
  |> Map.put(:node_color, "#6366f1")
)

Kino.VizJS.render(dot)

Highlighting Paths & Nodes

A common task is to highlight the result of an algorithm (e.g., a shortest path).

g = Yog.Generator.Classic.grid_2d(5, 5)
source = 0
target = 24

{:ok, path} = Yog.Pathfinding.shortest_path(in: Yog.Builder.GridGraph.to_graph(g), from: source, to: target)

# Use path_to_options for automatic highlighting
opts = Yog.Render.DOT.path_to_options(path, Yog.Render.DOT.theme(:presentation))
dot = Yog.Render.DOT.to_dot(g, opts)

Kino.VizJS.render(dot)

Per-Node and Per-Edge Styling

Use callback functions for fine-grained control:

g = Yog.directed()
  |> Yog.add_node(1, %{name: "Alice", role: "Admin"})
  |> Yog.add_node(2, %{name: "Bob", role: "User"})
  |> Yog.add_node(3, %{name: "Carol", role: "Admin"})
  |> Yog.add_edges!([{1, 2, %{action: "Deletes"}}, {2, 3, %{action: "Views"}}])

node_attrs = fn id, data ->
  case data.role do
    "Admin" -> [{:fillcolor, "#ef4444"}, {:style, "filled"}]
    "User" -> [{:fillcolor, "#3b82f6"}, {:style, "filled"}]
    _ -> []
  end
end

edge_attrs = fn _from, _to, weight ->
  case weight.action do
    "Deletes" -> [{:color, "#ef4444"}, {:penwidth, 2}]
    _ -> [{:color, "#94a3b8"}]
  end
end

dot = Yog.Render.DOT.to_dot(g,
  Yog.Render.DOT.default_options()
  |> Map.put(:node_attributes, node_attrs)
  |> Map.put(:edge_attributes, edge_attrs)
)

Kino.VizJS.render(dot)

Subgraphs and Clusters

Group nodes visually using subgraphs:

g = Yog.directed()
  |> Yog.add_node(:api, "API Gateway")
  |> Yog.add_node(:auth, "Auth Service")
  |> Yog.add_node(:db, "Database")
  |> Yog.add_node(:cache, "Cache")
  |> Yog.add_edges!([{:api, :auth, 1}, {:auth, :db, 1}, {:api, :cache, 1}])

opts = %{
  Yog.Render.DOT.default_options()
  | subgraphs: [
      %{
        name: "cluster_backend",
        label: "Backend Services",
        node_ids: [:auth, :db],
        style: :filled,
        fillcolor: "#e0f2fe",
        color: "#0284c7"
      }
    ]
}

Kino.VizJS.render(Yog.Render.DOT.to_dot(g, opts))

Theming

Yog comes with several built-in themes:

g = Yog.Generator.Classic.binary_tree(3)

# 1. Dark Theme
dot_dark = Yog.Render.DOT.to_dot(g, Yog.Render.DOT.theme(:dark))
Kino.VizJS.render(dot_dark)

# 2. Minimal Theme
dot_min = Yog.Render.DOT.to_dot(g, Yog.Render.DOT.theme(:minimal))
Kino.VizJS.render(dot_min)

# 3. Presentation Theme
dot_pres = Yog.Render.DOT.to_dot(g, Yog.Render.DOT.theme(:presentation))
Kino.VizJS.render(dot_pres)

Mermaid.js Rendering

Mermaid is perfect for embedding diagrams in Markdown, GitHub, Notion, and documentation.

Basic Mermaid

g = Yog.directed()
  |> Yog.add_edges!([
    {"Start", "Process", 1},
    {"Process", "End", 1}
  ])

mermaid = Yog.Render.Mermaid.to_mermaid(g)
IO.puts(mermaid)

Mermaid Themes

# Dark theme for dark-mode documentation
mermaid_dark = Yog.Render.Mermaid.to_mermaid(g, Yog.Render.Mermaid.theme(:dark))
IO.puts(mermaid_dark)

Mermaid with Custom Styling

g = Yog.directed()
  |> Yog.add_node(:server, "Server")
  |> Yog.add_node(:db, "Database")
  |> Yog.add_edge_ensure(:server, :db, "SQL")

node_attrs = fn id, _data ->
  case id do
    :server -> [{:fill, "#dbeafe"}, {:stroke, "#2563eb"}]
    :db -> [{:fill, "#dcfce7"}, {:stroke, "#16a34a"}]
    _ -> []
  end
end

mermaid = Yog.Render.Mermaid.to_mermaid(g,
  Yog.Render.Mermaid.default_options()
  |> Map.put(:node_attributes, node_attrs)
  |> Map.put(:node_shape, :cylinder)
)
IO.puts(mermaid)

Algorithm Helper Options

Yog provides convenience functions to highlight algorithm results:

# 1. MST highlighting
weighted = Yog.from_edges(:undirected, [
    {:a, :b, 4}, {:a, :h, 8}, {:b, :c, 8},
    {:c, :d, 7}, {:c, :f, 4}, {:d, :e, 9},
    {:e, :f, 10}, {:f, :g, 2}, {:g, :h, 1}
  ])

{:ok, mst} = Yog.MST.kruskal(in: weighted)
mst_opts = Yog.Render.DOT.mst_to_options(mst, Yog.Render.DOT.theme(:minimal))
Kino.VizJS.render(Yog.Render.DOT.to_dot(weighted, mst_opts))

# 2. Community highlighting
sbm = Yog.Generator.Random.sbm([8, 8], [[0.8, 0.1], [0.1, 0.8]])
comm = Yog.Community.Louvain.detect(sbm)
comm_opts = Yog.Render.DOT.community_to_options(comm)
Kino.VizJS.render(Yog.Render.DOT.to_dot(sbm, comm_opts))

# 3. Min-Cut highlighting
flow = Yog.directed()
  |> Yog.add_edges!([{:s, :a, 10}, {:s, :b, 10}, {:a, :t, 10}, {:b, :t, 5}])

result = Yog.Flow.MaxFlow.dinic(flow, :s, :t)
min_cut = Yog.Flow.MaxFlow.min_cut(result)
cut_opts = Yog.Render.DOT.cut_to_options(min_cut)
Kino.VizJS.render(Yog.Render.DOT.to_dot(flow, cut_opts))

Summary

Customizing visualizations in Yog is highly flexible:

1. Global Attributes: Control layout, background, and defaults via the options map.
2. Highlighting: Use path_to_options, mst_to_options, community_to_options, cut_to_options.
3. Data-Driven Styling: Use callback functions for per-node and per-edge attributes.
4. Subgraphs: Group nodes visually into clusters.
5. Themes: Use professionally curated presets for DOT and Mermaid.
6. Dual Formats: Export to Graphviz DOT (rich) or Mermaid.js (portable).

In the next "How-To", we'll look at Importing and Exporting graphs in formats like GraphML and JSON.