Highlighting

It is common to make a Node (or a part of a Node or a Link) stand out by "highlighting" it in some way. This happens with selection when a selection Adornment is shown. However one frequently wants to highlight Parts independently of selection. This can be done by changing the fill or stroke of a Shape, replacing a Picture source with another source, adding or removing a shadow, and so on.

Highlighting a Node upon Mouse Over

The most general kind of highlighting is to change appearance when an action occurs, such as mousing over a node. This can draw attention to interactive Nodes or Links or really any GraphObject, such as buttons. This is why predefined buttons in GoJS highlight on mouse-over.

To achieve this effect you just need to define GraphObject.mouseEnter and GraphObject.mouseLeave event handlers.

  diagram.initialContentAlignment = go.Spot.Center;

  function mouseEnter(e, obj) {
    var shape = obj.findObject("SHAPE");
    shape.fill = "#6DAB80";
    shape.stroke = "#A6E6A1";
    var text = obj.findObject("TEXT");
    text.stroke = "white";
  };

  function mouseLeave(e, obj) {
    var shape = obj.findObject("SHAPE");
    // Return the Shape's fill and stroke to the defaults
    shape.fill = obj.data.color;
    shape.stroke = null;
    // Return the TextBlock's stroke to its default
    var text = obj.findObject("TEXT");
    text.stroke = "black";
  };

  diagram.nodeTemplate =
    $(go.Node, "Auto",
      {
        mouseEnter: mouseEnter,
        mouseLeave: mouseLeave
      },
      $(go.Shape, "Rectangle",
        { strokeWidth: 2, stroke: null, name: "SHAPE" },
        new go.Binding("fill", "color")),
      $(go.TextBlock,
        { margin: 10, font: "bold 18px Verdana", name: "TEXT" },
        new go.Binding("text", "key"))
    );

  diagram.model = new go.GraphLinksModel(
  [
    { key: "Alpha", color: "#96D6D9" },
    { key: "Beta",  color: "#96D6D9" },
    { key: "Gamma", color: "#EFEBCA" },
    { key: "Delta", color: "#EFEBCA" }
  ],
  [
    { from: "Alpha", to: "Beta" },
    { from: "Alpha", to: "Gamma" },
    { from: "Beta", to: "Beta" },
    { from: "Gamma", to: "Delta" },
    { from: "Delta", to: "Alpha" }
  ]);

Mouse-over nodes to see them highlight.

It is also commonplace to perform highlighting of stationary Parts during a drag, which is a different case of "mouse over". This can be implemented in a manner similar to the mouseEnter/mouseLeave events by implementing GraphObject.mouseDragEnter and GraphObject.mouseDragLeave event handlers. Several samples demonstrate this: Org Chart Editor, Planogram, Regrouping, and Seating Chart.

Highlighting Nodes and Links

It is common to want to show Nodes or Links that are related to a particular Node. Unlike the mouse-over scenarios, one may want to maintain the highlighting for many Parts independent of any mouse state or selection state.

Here is an example of highlighting all of the nodes and links that come out of a node that the user clicks. This example uses the Part.isHighlighted property and data binding of visual properties to that Part.isHighlighted property.

  diagram.initialContentAlignment = go.Spot.Center;

  diagram.nodeTemplate =
    $(go.Node, "Auto",
      { // when the user clicks on a Node, highlight all Links coming out of the node
        // and all of the Nodes at the other ends of those Links.
        click: function(e, node) { showConnections(node); }  // defined below
      },
      $(go.Shape, "Rectangle",
        { strokeWidth: 2, stroke: null },
        new go.Binding("fill", "color"),
        // the Shape.stroke color depends on whether Node.isHighlighted is true
        new go.Binding("stroke", "isHighlighted", function(h) { return h ? "red" : "black"; })
            .ofObject()),
      $(go.TextBlock,
        { margin: 10, font: "bold 18px Verdana" },
        new go.Binding("text", "key"))
    );

  // define the Link template
  diagram.linkTemplate =
    $(go.Link,
      { routing: go.Link.Normal, toShortLength: 4, selectable: false },
      $(go.Shape,
        { isPanelMain: true, stroke: "black", strokeWidth: 1 },
        // the Shape.stroke color depends on whether Link.isHighlighted is true
        new go.Binding("stroke", "isHighlighted", function(h) { return h ? "red" : "black"; })
            .ofObject()),
      $(go.Shape,
        { toArrow: "standard", stroke: null, strokeWidth: 0 },
        // the Shape.fill color depends on whether Link.isHighlighted is true
        new go.Binding("fill", "isHighlighted", function(h) { return h ? "red" : "black"; })
            .ofObject())
    );

  // highlight all Links and Nodes coming out of a given Node
  function showConnections(node) {
    var diagram = node.diagram;
    diagram.startTransaction("highlight");
    // remove any previous highlighting
    diagram.clearHighlighteds();
    // for each Link coming out of the Node, set Link.isHighlighted
    node.findLinksOutOf().each(function(l) { l.isHighlighted = true; });
    // for each Node destination for the Node, set Node.isHighlighted
    node.findNodesOutOf().each(function(n) { n.isHighlighted = true; });
    diagram.commitTransaction("highlight");
  }

  // when the user clicks on the background of the Diagram, remove all highlighting
  diagram.click = function(e) {
    diagram.startTransaction("no highlighteds");
    diagram.clearHighlighteds();
    diagram.commitTransaction("no highlighteds");
  };

  diagram.model = new go.GraphLinksModel(
    [
      { key: "Alpha", color: "#96D6D9" },
      { key: "Beta",  color: "#96D6D9" },
      { key: "Gamma", color: "#EFEBCA" },
      { key: "Delta", color: "#EFEBCA" }
    ],
    [
      { from: "Alpha", to: "Beta" },
      { from: "Alpha", to: "Gamma" },
      { from: "Beta", to: "Beta" },
      { from: "Gamma", to: "Delta" },
      { from: "Delta", to: "Alpha" }
    ]);

Click on a node to highlight outbound connected links and nodes. Click in the diagram background to remove all highlights. Note that the highlighting is independent of selection.

The use of data binding to modify the Shape properties allows you to avoid specifying names for each Shape and writing code to find the Shape and modify its properties.