CSS Houdini is a set of APIs that allow developers to directly manipulate and extend the browser's style processing process through JavaScript. 1. Paint Worklet controls element drawing; 2. Layout Worklet custom layout logic; 3. Animation Worklet implements high-performance animation; 4. Parser & Typed OM efficiently operates CSS properties; 5. Properties & Values ??API registers custom properties; 6. Font Metrics API obtains font information. It allows developers to expand CSS in unprecedented ways, achieving effects such as wave backgrounds, and has advantages such as good performance, high flexibility, and clear standardized paths, but it also faces challenges such as poor compatibility and steep learning curve. Currently, we can start with Paint Worklet and try it step by step in combination with experimental projects.

CSS Houdini APIs are a set of browser interfaces that open the "black box" of the CSS engine for developers, allowing you to directly operate and extend the browser's style processing process using JavaScript. This means that you are no longer just using CSS, but you can participate in defining how it works.

Does this sound a bit abstract? In fact, its core goal is very clear: to enable developers to customize how the browser parses, lays out and draws elements, so as to achieve some effects that could only be achieved by hacks or images before.

What is CSS Houdini?

Houdini is a set of W3C standardized APIs, named after the famous escape guru Harry Houdini, meaning "escape from the limitations of CSS." It is not a single set of tools, but a collection of projects, each part solving problems at a specific stage:

• Paint Worklet : Controls the drawing process of elements, such as drawing a rounded corner gradient background.
• Layout Worklet : Customize the layout logic of elements, such as implementing a new flex or grid layout.
• Animation Worklet : Run high-performance animations outside the main thread.
• Parser & Typed OM : Read and write CSS property values ??more efficiently.
• Properties & Values ??API : Register custom CSS properties and assign type information to facilitate calculation.
• Font Metrics API : Get detailed metrics for fonts.

These APIs work together to allow you to insert your own code at different stages of your browser's rendering process.

How do developers use Houdini to extend CSS?

The biggest highlight of Houdini is that it allows you to "write" into the CSS engine itself. Traditional CSS extensions rely on preprocessors (such as Sass) or JS manipulation DOM styles, but these all happen outside the engine. Houdini provides the ability to directly intervene in the rendering process.

For example: You want to implement a completely new type of background pattern, such as wavy line filling. In the past, you might have to add SVG with pseudo-elements, but now you can customize the drawing logic with Paint Worklet and use it like this:

 .my-element {
  background: paint(wavy-pattern);
}

This is just the tip of the iceberg. With the increase in support, new features like CSS Grid can even be developed in the future without waiting for the standard update.

Benefits and challenges in practical applications

benefit:

• Better performance : Many Houdini functions run on independent threads (such as Worklets) and do not block the main thread.
• More flexibility : You can do a lot of things that native CSS doesn't support yet, such as dynamically responding to container size changes to adjust the layout.
• Clear standardized path : Once a feature is widely used, it has the potential to become part of the new CSS standard.

challenge:

• Poor compatibility : Currently, mainstream browsers support Houdini is not perfect, especially Layout Worklet.
• Steep learning curve : You need to understand the multiple stages of the browser rendering process and how to collaborate with Worklets.
• Debugging Difficulty : Because it is running in a Worklet, traditional debugging tools may not be able to directly track the problem.

How to start trying Houdini?

If you are interested, you can start from the following directions:

• Learning Paint Worklet is the most mature and easy-to-get-to-hand part at present.
• Use community-provided experimental libraries, such as Houdini Samples .
• Follow the update log of browser vendors to see which features are already available.
• Trial in experimental projects and don't rush to go online.

Basically that's it. Although it is not the stage of large-scale use, it is one of the important directions for CSS evolution. If you like to go deep into the underlying mechanism or want to do some truly “different” visuals, Houdini is worth a try.

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