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    D3.js and ELK based schematic visualizer.

    Use npm install d3-hwschematic --save to install this library and save it to your package.json file.


    • automatic layout (layered graph with orthogonal routing, created by elkjs) with caching
    • hierarchical components expandable on click
    • net selection on click, highligh and tooltip on mouse over
    • zoom, drag
    • css style/class specifiable in input json, d3.js querey as a query language in javascript
    • support for user node renderers and user CSS
    • input is ELK json with hwMeta propoperty (described in this document)


    Typical usecase

    How to use examples


    • Documentation of hwtLib. (Look for scheme href under component name.)

    • jupyter_widget_hwt - Jupyter widgets for hw developement.

    From this git

    1. download dependencies and build this library
    npm install
    npm install --only=dev
    npm run build
    1. Then you can open examples, but current web browsers does not allow to load files from local disk (because of security). It has multiple solution
    • You can run chrome with --allow-file-access-from-files option
    • (prefered) Or use webserver. One webserver implementation is part of standard python distribution.
    # (in root directory of this git)
    python3 -m http.server 8888

    Now you should be able to view the example application on Where part after schematic= is path to json file where schematic is stored.

    ELK json format for d3-hwschematic

    This libarary uses ELK json, ELK options. This format is basically a component tree stored in json. The json specifies not just the structure of circuit but also how the circuit should be rendered. It contains 3 object types LNode, LPort and LEdge.

    ELK LNode (component instance)

      "id": "0",
      "hwMeta": { // [d3-hwschematic specific]
        "name": "compoent instance name", // optional str
        "cls": "compoent (module) name", // optional str
        "bodyText": "", // optional str
        "maxId": 2, // max id of any object in this node used to avoid re-counting object if new object is generated
        "isExternalPort": true // optional flag which set component style to external port
        "cssClass": "node-style0", // optional string, css classes separated by space
        "cssStyle": "fill:red", // css style specification separated by ;
      "hideChildren": true, // [d3-hwschematic specific] optional flag, if true the body of component is collapsed
      "properties": { // recommended renderer settings
        "org.eclipse.elk.portConstraints": "FIXED_ORDER", // can be also "FREE" or other value accepted by ELK
        "org.eclipse.elk.layered.mergeEdges": 1
      "ports": [],    // list of LPort
      "edges": [],    // list of LEdge
      "children": [], // list of LNode, if the node should be collapsed rename this property
                      // to "_children" and "edges" to "_edges"

    If the children should be collapsed by default, the children children and edges property should be renamed to _children and _edges.

    ELK LPort

      "id": "1",
      "hwMeta": { // [d3-hwschematic specific]
        "name": "port name",
        "cssClass": "node-style0", // optional string, css classes separated by space
        "cssStyle": "fill:red", // css style specification separated by ;
        "connectedAsParent": true, // an optional flag that notes that this port
                                   // has no connections but it is connected as its parent port
      "direction": "OUTPUT", // [d3-hwschematic specific] controlls direction marker
      "properties": {
        "portSide": "EAST",
        "portIndex": 0 // The order is assumed as clockwise, starting with the leftmost port on the top side.
                       // Required only for components with "org.eclipse.elk.portConstraints": "FIXED_ORDER"
      "children": [], // list of LPort, if the port should be collapsed rename this property to "_children"

    ELK LEdge

    { // simple LEdge
      "id": "62",
      "source": "2", // id of component
      "sourcePort": "23", // id of component port
      "target": "4", // id of component
      "targetPort": "29", // id of component port
      "hwMeta": { // [d3-hwschematic specific]
        "name": null // optional string, displayed on mouse over
        "cssClass": "link-style0", // optional string, css classes separated by space
        "cssStyle": "stroke:red", // css style specification separated by ;
    { // hyper LEdge
      "id": "1119",
      "sources": [
        ["17", "343"]  // id of component, id of port
      "targets": [
        [ "18", "346"],  // id of component, id of port
        [ "21", "354"],
      "hwMeta": { // [d3-hwschematic specific]
        "name": "wr_ptr",
        "cssClass": "link-style0", // optional string, css classes separated by space
        "cssStyle": "stroke:red", // css style specification separated by ;

    LEdge souce destination has to always be directly visible from the LNode where the LEdge is instanciated. That means that LEdge may connect only to ports of current LNode or to ports of this LNode direct children LNodes. LNode represents all types of components. Top component ports are also represented as LNode because it looks better.

    Component shapes

    The style and shape is determined by node renderers. Node renderers are defined in src/node_renderers. Renderer classes can be registered using HwSchematic.nodeRenderers.registerRenderer() function on HwSchematic object. The node renderer has function select which is used to determine if renderer should be used for for selected LNode.

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