DotSharp.Core 0.1.0

DotSharp.Core

A clean-room C# reimplementation of the GraphViz dot engine — the hierarchical (layered, Sugiyama-style) layout algorithm for directed graphs from Gansner, Koutsofios, North & Vo, "A Technique for Drawing Directed Graphs" (IEEE TSE, 1993).

Parse the DOT language, lay the graph out with the same five-phase pipeline GraphViz uses, and emit SVG, GraphViz -Tplain / -Tdot, or just the computed coordinates to render however you like — all in managed code, no native dot.exe required at runtime.

Install

dotnet add package DotSharp.Core

Targets netstandard2.1 and net8.0. Pulls in SkiaSharp for the optional native (non-SVG) render backend; if you only need coordinates or SVG you can ignore it.

Quick start

using DotSharp.Dot;
using DotSharp.Layout;
using DotSharp.Render;

var graph   = DotParser.Parse("digraph { a -> b -> c; a -> c; }");
var layout  = LayoutEngine.Layout(graph);          // ranks + X/Y
var splines = SplineRouter.Route(graph, layout);   // edge routes

// 1) Render to SVG
string svg = SvgRenderer.Render(graph, layout, splines);

// 2) …or emit GraphViz-compatible plain text  (-Tplain)
string plain = PlainWriter.Write(graph, layout, splines);

// 3) …or read the coordinates yourself
foreach (var n in layout.Nodes)
{
    if (n.IsVirtual) { continue; }                 // skip long-edge waypoints
    Console.WriteLine($"{n.Original!.Name}: ({n.X}, {n.Y})");
}

What it does

A faithful re-creation of the dot pipeline:

1. acyclic — break cycles by reversing back edges.
2. rank — integer ranks via network simplex (low/lim + cut-value recurrence + rank balancing); virtual nodes inserted so every edge spans one rank.
3. mincross — within-rank ordering by median + transpose (brute-force-optimal on small ranks).
4. position — X by network simplex on the auxiliary graph + balancing sweeps; Y from rank × ranksep.
5. splines — edges routed as Bézier splines (Schneider box-fit) through the inter-rank channels.

Plus a DOT parser (scoping, ports, clusters, strict, rank=same/min/max), record/Mrecord labels, polygon & named shapes, arrowheads, styles, multi-line labels, cluster boxes, disconnected- component packing, and Times-New-Roman-calibrated node sizing.

Fidelity

Output is diffed against the real dot.exe in the test suite:

• Ranks — exact match.
• Crossings — ≤ dot, and provably optimal on small graphs.
• Node sizing — ~99% (box) / ~96% (ellipse); bounding box within ~1%.

Remaining differences are sub-pixel numerical tie-breaks (inherent to non-unique optima — two GraphViz builds differ there too) and HTML-<table> labels, which are not implemented.

License & provenance

MIT. DotSharp is written from the published papers and the public DOT language spec; the GraphViz source (EPL/CPL) is consulted only to understand behavior, never transliterated.