Visualization Workflow

Purpose of visualizations

Visualizations have two main purposes:

  • Display results of nodes
    Each node can be assigned with one or more visualization. After a node computes its new value, the visualization shows it in an understandable way to the user. Please note that a single node can be assigned with multiple visualizations at the same time. For example, a node might want to display a map of locations, and their list at the same time next to each other.

  • Provide interactive way to generate new data
    In a widget mode (described in detail later), visualizations provide users with an interactive GUI to define data. For example, a map visualization can both display locations, as well as allowing the user to pick locations by clicking with a mouse. Similarly, the histogram can both display a list of numbers, and can be manually draw with the mouse producing such a list. Several numbers can be visualized as a table of sliders, which can also be used to interactively generate a table of numbers. Image visualizations can behave like an image editor, etc.

Visualization Display Forms

Visualizations can be displayed in the following ways:

  • Attached to nodes In this mode, visualizations display the most recent result of the node. They behave like an integrated part of the node. Whenever you move the node, the visualization moves as well. This mode can be toggled by tapping the spacebar.

  • Fullscreen
    Visualization attached to node can grow (animate) to ocupy full IDE visual space. This mode can be triggered on the recently selected node (in case many nodes are selected, the last selected node will be used) by either pressing keeping the spacebar pressed for longer than approx 0.5s, or by tapping it twice. In the former case, the visualization shrinks to each original form whenever we release space, in the later, whenever we press space again.

  • Detached
    Visualizations attached to nodes can be detached, scaled, and placed freely across the visual canvas (we might introduce a special place where you can put such visualizations). This is useful when defining dashboards or reports. We also plan to provide a notebook-like experience where you can write text mixed with visualizations (including widgets for an interactive experience).

  • Widgets
    In this mode visualizations behave like nodes but do not display expressions. They have one input and one output port. If the input port is connected, the visualization displays its value and passes its to the output port. In case it is not connected, the visualization becomes an interactive widget allowing the user to specify data. For example, a map visualization will allow the user to manually pick locations. After each change, the new locations will be sent to the output port. Under the hood, widgets are represented as nodes and their code lines are assigned with a dedicated “visualization” metadata. Visualizations generate expressions always in the form of name = data, where data is a hardcoded data produced from the visualization. For example, when user clicks the map to define locations, the data could be a string literal containing locations encoded in JSON.

Choosing a Visualization Type.

When a new data is provided to a visualization, the visualization registry searches for all visualizations that match it (see visualization registry to learn more). For example, when a data of type [Int] (list of ints) is produced, all visualizations which matches [Int], like [Int], [a], or a will be found. Each type can be associated with a default visualization. For example, [Int] might define that its default visualization is a plot. If no default visualization is defined, a JSON visualization is used. Each visualization has a drop-down menu allowinh the user switching to another visualization type.

Active Visualizations

When visualizations are displayed on the stage, they are not active by default, which means, they do not capture keyboard shortcuts. Visualization becomes active when user clicks it. Visualizations are deactivated by clicking in the background of the node editor. When a visualization is active, all other elements should be slightly dimmed, or the visualization should get a selection border (to be defined). Active visualizations capture all keyboard shortcuts, but the space bar presses. Fullscreen visualizations are considered active by default.

HTML and Native Visualizations

There are two main types of visualizations - Html and Native. The later uses the BaseGL shape API to draw on the screen. We prefer the later as it integrates tightly with our framework and allows for much better performance. However, there is already many visualizations in HTML/JS and we need to provide support for them as well. HTML visualizations are required to be displayed in dedicated div elements. This has several consequences. Firstly, the browser needs to layout them, taking into account the current camera view, etc. It is costly. Refreshing CSS3D styles of 100 visualizations can absolutely kill the interactive performance. On the other hand, refreshing the position of 10k Native visualizations is almost free. Secondly, they need to be handled by our engine in such way that we can interact with them. For that purpose, the current Scene implementation defines three layers - top HTML layer, middle WebGL layer, and bottom HTML layer. The HTML visualizations are created and displayed on the bottom layer by default. Whenever an HTML visualization gets active, it should be moved to the top layer.

Visualization Registry

Visualizations are user-defined. Enso ships with a set of predefined visualizations, but they are in no way different than user-defined, they are just defined for you. Visualizations can be defined either as HTML or native visualization and can be defined in JS or WASM (or any language that compiles to one of these). Visualizations are stored on disk on the server-side and are provided to the GUI by the server. Users can upload their custom visualizations as well. Each visualization is registered in the visualization map. The map maps an Enso type to a set of visualizations defined for that type. The type might be very generic, like [a] (which in Enso terms means list of any elements).

Defining a Visualization

Currently only JavaScript visualizations can be defined. Support for native visualizations is planned.

Defining a JavaScript Visualization

JavaScript visualizations are defined by placing *.js files in the visualization subfolder in the project’s root directory. As IDE currently allows only editing Main.enso file, users have to create .js file manually, editing it outside IDE.

Custom JavaScript Visualization Example

Every visualization must reside in the visualization folder of the user’s project. For instance:

└─ Project_Name
   ├─ src
   │  └─ Main.enso
   └─ visualization
      └─ bubble.js

Visualizations can be defined as a JavaScript function which returns a class of a shape specified below. Consider the following sample definition:

console.log("Hi, this definition is being registered now!");

return class BubbleVisualization extends Visualization {
  static inputType = "Any";

  onDataReceived(data) {
    const xmlns = "";
    while (this.dom.firstChild) {
    const width = this.dom.getAttributeNS(null, "width");
    const height = this.dom.getAttributeNS(null, "height");
    const svgElem = document.createElementNS(xmlns, "svg");
    svgElem.setAttributeNS(null, "id", "vis-svg");
    svgElem.setAttributeNS(null, "viewBox", "0 0 " + width + " " + height);
    svgElem.setAttributeNS(null, "width", "100%");
    svgElem.setAttributeNS(null, "height", "100%");
    data.forEach((data) => {
      const bubble = document.createElementNS(xmlns, "circle");
      bubble.setAttributeNS(null, "stroke", "black");
      bubble.setAttributeNS(null, "fill", "red");
      bubble.setAttributeNS(null, "r", data[2]);
      bubble.setAttributeNS(null, "cx", data[0]);
      bubble.setAttributeNS(null, "cy", data[1]);

  setSize(size) {
    this.dom.setAttributeNS(null, "width", size[0]);
    this.dom.setAttributeNS(null, "height", size[1]);

In particular:

  • [Required] Source code

    Visualization definition has to be a valid body of JavaScript function which returns a class definition. Instances of that class will be considered separate visualizations. You are allowed to use global variables / global state across visualizations of the same type, but you are highly advised not to do so.

  • [Required] Visualization superclass

    The class returned by the definition function should extend the predefined Visualization class. Classes which do not extend it, will not be registered as visualizations. The superclass defines a default constructor and a set of utilities:

    • Method setPreprocessorCode(code)

      Set an Enso code which will be evaluated on the server-side before sending data to visualization. If not called, a default unspecified code is used that will provide some JSON representation of the value. See Lazy visualizations section for details.

    • Method setPreprocessorModule(module)

      Define in which module’s context the preprocessor code should be evaluated. If not called, the Main module of the project that defines visualization will be used. See Lazy visualizations section for details.

    • Method setPreprocessor(code,mode)

      Set both code and its module context at once. If both need to be updated, using this method can save an update processing and needless evaluation. Note that using both setPreprocessorCode and setPreprocessorModule from the visualization’s custom constructor will not cause any unnecessary updates, as the preprocessor is applied only after visualization is fully constructed. See Lazy visualizations section for details.

    • Field dom

      It is initialized in the constructor to the DOM symbol used to host the visualization content. Users are free to modify the DOM element, including adding other elements as its children.

    • Field theme

      The IDE’s current color theme. Exposes the following methods.

      • Method getColorForType

        Takes a qualified type name and returns the color that is used in the GUI to represent that type.

      • Method getForegroundColorForType

        Takes a qualified type name and returns the color that should be used for foreground elements (e.g. text) that are shown on top of the background color returned by getColorForType.

      • Method get

        Takes a style sheet path as string and returns the corresponding value from the theme. For example, get("graph_editor.node.error.panic") returns the orange color that is used to mark nodes in an error state.

  • [Optional] Field label

    The static field label is an user-facing name used to identify the visualization. You are not allowed to define several visualizations of the same name in the same Enso library. In case the field is missing, the name will be inferred from the class name by splitting the camel-case name into chunks and converting them to lowercase string.

  • [Optional] Field inputType

    The static field inputType is used to determine which Enso data types this visualization can be used for. Its value should be a valid Enso type, like "String | Int". In case the field is an empty string or it is missing, it will default to "Any", which is a type containing all other types. It is a rare case when you want to define a visualization which is able to work with just any data type, so you are highly advised to provide the type definition.

  • [Optional] Field inputFormat

    The static field inputFormat is used to determine what format the data should be provided to the onDataReceived function. Currently, the only valid option is “json”, but it will be possible to set it to “binary” in the future. In the later case, it is up to the visualization author to manage the binary stream received from the server.

  • [Optional] Constructor

    The visualization will be instantiated by providing the constructor with a configuration object. The shape of the configuration object is not part of the public API and can change between releases of this library. You have to pass it unchanged to the superclass constructor.

  • [Optional] Function onDataReceived

    The onDataReceived(data) method is called on every new data chunk received from the server. Note that the visualization will receive the “full data” if you are not using the setPreprocessor method.

  • [Optional] Function setSize

    The setSize(size) method is called on every size change of the visualization. You should not draw outside of the provided area, however, if you do so, it will be clipped to the provided area automatically. The size parameter contains two fields width and height expressed in pixels.

Sending Data to Visualizations

Lazy Visualizations

Very important information is how visualization architecture works to make them interactive and fast. Whenever new data is computed by the compiler and visualization is attached to it, it is sent to GUI to be displayed. However, sending huge chunks of data will kill the performance. When defining a visualization user is capable of defining a chunk of Enso code (as a string). This code is part of the visualization definition and is stored server-side. Visualizations are allowed to change the code at runtime (in JavaScript visualization you may use the setPreprocessor method). This code defines an Enso function, which will be run by the compiler on data the visualization is attached to. Only the results of this code will be sent to the GUI. In the case of the JSON input format, the result of the call should be a valid JSON string. The code will be evaluated in the context of the Main module in the project where visualization is defined - you may use any symbol defined or imported in that module.

For example, imagine you want to display a heatmap of 10 million points on a map, and these points change rapidly. Sending such an amount of information via WebSocket could be too much, and you (as the visualization author) might decide that the visualization image should be generated on the server, and your visualization is meant only to display the resulting image. In such a scenario, you can define in your visualization an Enso function which will compute the the image on the server!

Binary and Text (JSON) Formats

Each visualization can choose whether it supports either binary or JSON input. The input format defaults to JSON. The data from the server is always sent to GUI in a binary channel, however, when JSON format is selected, it is first converted to JSON representation on the server side. We can assume that all Enso data types have defined conversion to JSON by default. If the visualization input is defined as JSON input, the binary stream will be converted to JSON by the GUI engine before passing to visualization. It is up to the visualization author to handle the textual or binary form.

Builtin Visualizations

IDE comes with a set of predefined visualizations, including charts.

Dataframes Support

Some of the predefined visualizations have some special support for Table from Enso Dataframes library.


When using Histogram visualization on a Table value it will first look for a column named value. If present, it will be used as a data source. Otherwise, Histogram will use the first numerical column.

Scatter Plot

The Scatter Plot visualization has several properties for each point. If a column of a matching name is present in the Table it will be used.

  • x — position on horizontal axis. If not present, the index column will be used. If there is no index set, the row indices will be used. If this column has a missing value, the point will be omitted.
  • y — position on vertical axis. If not present, first numerical column of unrecognized name will be used. If not present, first numerical column will be used. If this column has a missing value, the point will be omitted.
  • color — color of the point. The default color is black and will be used if column is not present or for its missing values. color should be a Text column with elements being in a CSS colors format:
    • Hexadecimal formats, like #RGB, #RRGGBB and #RRGGBBAA.
    • RGB function-like syntax, e.g. rgb(255,0,128) or rgba(255,0,128,0.5).
    • HSL function-like syntax, e.g. hsl(120, 100%, 50%) or hsla(120, 100%, 50%, 0.3).
    • name of one of predefined colors, e.g. red or SteelBlue.
  • label — text to be displayed next to the point.
  • shape — shape of the point. Supported shapes are:

    • cross;
    • diamond;
    • square;
    • star;
    • triangle.

    The default shape is a circle.

  • size — size of the point as a (possible floating point) number. Default size of the point is 1.0.