Frequently Asked Questions:
- What is the Emacs Widget Library used for? The Emacs Widget Library is used to create form-like interfaces within Emacs, powering the Customize interface and various other packages that require user input through forms.
- What are the main limitations of the Emacs Widget Library? The main limitations include a lack of modern UI layout controls, poor state management capabilities, and complex inheritance for widget types which can complicate development of more sophisticated interfaces.
- How does the Emacs Widget Library perform with large numbers of widgets? Despite its architectural simplicity, the library handles large numbers of widgets efficiently without needing heavy GUI objects or a separate rendering pipeline, as demonstrated by the Customize interface.
- What is widget-extra? Widget-extra is a library created by the author to extend the built-in Emacs Widget Library, adding more complex UI components like editable tables and field groups with aligned tags.
- What is vui.el? Vui.el is a new UI layer that uses the Emacs Widget Library under the hood but provides higher-level abstractions for easier UI development, including declarative composition and automatic state management.
Summary
The Emacs Widget Library, essential for form-like interfaces in Emacs, has remained relatively unchanged since its inception in 1996. This post delves into the practical experiences of building complex user interfaces using this library, highlighting both its underappreciated capabilities and significant limitations. Through a detailed critique and personal case studies, the author illustrates the challenges faced, such as poor documentation, lack of layout controls, and cumbersome state management. The exploration includes a discussion on the library's deep integration with Emacs, performance efficiency, and the classical inheritance approach in widget type definitions, juxtaposed with modern UI development practices.
Highlights:
- Widgets integrate deeply with Emacs, functioning efficiently across both GUI and terminal interfaces.
- The library supports creating and managing a wide range of widget types through inheritance.
- Documentation gaps and complex code navigation significantly increase the learning curve.
- Lacks modern UI layout and state management features, making complex UI development cumbersome.
- Extended functionality through widget-extra library and new vui.el layer for better UI development.
The Emacs Widget Library, integral to the Emacs environment, facilitates the development of form-like interfaces but has seen little change since its creation by Per Abrahamsen in 1996. It is fundamentally built on Emacs's philosophy that 'everything is a buffer,' allowing widgets to be treated as text with properties. This design choice ensures performance but restricts flexibility in UI design, lacking features like a layout engine or reactive state management. The library excels in managing simple UI elements like buttons and fields but struggles with complex, interdependent widgets or dynamic UIs.
The critique provided in the post is based on firsthand development experiences, particularly in extending the library's capabilities through the 'widget-extra' library for building more complex UI elements like tables and aligned fields. These extensions demonstrate both the potential and limitations of the original library, highlighting issues such as the absence of a widget tree, manual state management, and the need for full redrawing of UIs for minor changes. The case study of building a table widget underscores the necessity of manual layout management, precise cursor control, and the lack of incremental updates.
Looking forward, the post introduces 'vui.el,' a new layer built on top of the widget library to simplify UI development in Emacs. This approach aims to retain the performance benefits of the existing system while reducing the complexity involved in UI creation. It offers more declarative composition, automatic state propagation, and cursor-aware redraws, presenting a more user-friendly approach to Emacs UI development. This evolution reflects a broader trend in software development towards more abstracted and efficient UI frameworks, addressing some of the foundational gaps in the original Emacs Widget Library.