Creating Custom Widgets in CesiumJS: A Developer's Toolkit

CesiumJS not only provides a rich set of built-in widgets for common tasks but also allows developers to create custom widgets tailored to their specific application needs. In this guide, we'll not only cover the fundamental steps for creating custom widgets but also explore the architecture of CesiumJS widgets and how to publish them for broader reuse.

Widget Architecture in CesiumJS

CesiumJS follows a modular widget architecture, treating each widget as an independent component. The characteristics of a CesiumJS widget include:

• Encapsulation of state and functionality.

• Exposure of public methods and properties for interaction.

• Event handling to notify changes in state.

• Styling capabilities using CSS.

• Integration with Cesium's scene and primitives.

Creating a Basic Custom Widget

Let's start by creating a simple HelloWidget that displays a greeting:

javascript

class HelloWidget {

constructor(options) {

this._container = document.createElement("div");

this._container.innerText = "Hello World!";

this._container.className = "cesium-helloWidget";

this._container.addEventListener("click", () => {

this._container.innerText = "Goodbye!";

});

}

get container() {

return this._container;

}

}

This widget encapsulates its state, exposes a container, and reacts to a click event to update its content.

Integrating with CesiumViewer

To integrate the widget with a CesiumViewer, pass it as an option during construction:

javascript

const viewer = new Cesium.Viewer("cesiumContainer", {

widget: new HelloWidget()

});

CesiumViewer will handle the automatic appending of the widget's container to the DOM.

Adding Custom Styles and Interactions

Enhance the widget by adding styles using CSS:

css

.cesium-helloWidget {

color: green;

font-size: 2em;

}

Additionally, listen to DOM events and update the widget's state:

javascript

class HelloWidget {

constructor(options) {

this._container = document.createElement("div");

this._container.innerText = "Hello World!";

this._container.className = "cesium-helloWidget";

this._container.addEventListener("click", () => {

this._container.innerText = "Goodbye!";

});

}

get container() {

return this._container;

}

}

Publishing the Widget for Reuse

To share your custom widget, follow these steps:

1. Export as a module

javascript

export default HelloWidget;

1. Publish on npm

bash

npm publish

1. Document API and examples in README

Provide clear documentation on how to use the widget, its API, and include examples in the README file.

1. Mention licensing and contribution guidelines

Clearly state the licensing terms and guidelines for contributions.

By following these steps, other developers can easily install and integrate your custom widget into their Cesium applications, fostering collaboration within the CesiumJS community.