#Milky2018/moon_elk

A MoonBit port of Eclipse Layout Kernel (ELK).

#Imports

In moon.pkg, import the packages you use:

import {
  "moonbitlang/core/json" @json,
  "Milky2018/moon_elk/core" @elk_core,
  "Milky2018/moon_elk/graph" @elk_graph,
  "Milky2018/moon_elk/graph/json" @elk_graph_json,
}

#Layout JSON with Core Engine

pub fn layout_json(input : String) -> String raise {
  let graph = @json.parse(input)
  @elk_core.new_elk_engine().layout(graph~).stringify()
}

#Run the Minimal Example

moon run src/examples/minimal/cmd

The example uses the full in-process engine and prints the layout result as JSON.

#Minimal Input Example

{
  "id": "root",
  "layoutOptions": {
    "elk.algorithm": "layered",
    "elk.direction": "DOWN"
  },
  "children": [
    { "id": "n1", "width": 80, "height": 40 },
    { "id": "n2", "width": 80, "height": 40 }
  ],
  "edges": [
    { "id": "e1", "sources": ["n1"], "targets": ["n2"] }
  ]
}

pub fn run_minimal_example() -> String raise {
  let input =
    "{\"id\":\"root\",\"layoutOptions\":{\"elk.algorithm\":\"layered\",\"elk.direction\":\"DOWN\"},\"children\":[{\"id\":\"n1\",\"width\":80,\"height\":40},{\"id\":\"n2\",\"width\":80,\"height\":40}],\"edges\":[{\"id\":\"e1\",\"sources\":[\"n1\"],\"targets\":[\"n2\"]}]}"
  layout_json(input)
}

#Build Graph Model and Export JSON

fn build_and_export() -> String {
  let root = @elk_graph.create_graph()
  let n1 = @elk_graph.create_node(Some(root))
  let n2 = @elk_graph.create_node(Some(root))
  ignore(@elk_graph.create_simple_edge(n1, n2))

  @elk_graph_json
    .elk_graph_json_for_elk_graph(root)
    .pretty_print(true)
    .to_json()
}

#Import JSON into Graph Model

fn import_graph(text : String) -> Int {
  @elk_graph_json.elk_graph_json_for_graph(text).to_elk()
}

#Algorithm Support (Core Engine)

Supported by new_elk_engine().layout:

layered
force
stress
radial
mrtree
rectpacking
sporeOverlap
sporeCompaction
fixed
box
random
vertiflex
disco
topdownpacking

Not supported (returns algorithm-not-found style errors):

libavoid
Graphviz family (dot, neato, fdp, sfdp, twopi, circo)

Graphviz algorithms can be registered explicitly by a host runtime that provides a process factory and DOT serializer/parser. They remain excluded from the default in-process engine. add_graphviz_layout_algorithms registers dot, neato, fdp, sfdp, twopi, and circo on a custom EngineBuilder. When a synchronous text runner is available, add_graphviz_layout_algorithms_with_text_runner configures the process factory and registers the family in one step.

Libavoid follows the same opt-in model. A host can configure a synchronous server factory and register libavoid explicitly on a custom EngineBuilder; it remains excluded from the default in-process engine. add_libavoid_layout_algorithm_with_text_runner combines both steps.

#Coordinate Semantics for Edges

ELK edge sections[*].startPoint/endPoint/bendPoints are in the coordinate system of edge.container (local coordinates), not always root-absolute coordinates.

When rendering, convert edge points to absolute coordinates by adding the accumulated parent offsets of edge.container.

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