What are Houdini APIs CSS?

Key takeaways
Houdini APIs enhance CSS by allowing developers to interact directly with the browser’s rendering engine.
The main types of Houdini API include Paint API, Parser API, Animation API, Typed OM API, and Layout API, each serving different styling needs.
They improve rendering efficiency, enabling smoother animations and faster load times.
Not all browsers support Houdini APIs, and there may be a learning curve for developers.

Houdini APIs are a collection of low-level interfaces for developers to enhance CSS by directly interacting with the browser’s rendering engine. These APIs enable developers to modify the styling and layout of webpages in ways that were once difficult or impossible using standard CSS. Let’s explore the functionality of Houdini APIs a bit more deeply.

Motivation behind Houdini APIs

The development of Houdini APIs started as a collaborative effort between browser vendors and the web development community to create a more extensible styling system. The initiative aimed to provide a way to implement custom CSS features that could be standardized and widely adopted. These APIs were developed to fill the gap between CSS’s native capabilities and the advanced styling requirements of modern web applications. They provide the essential tools for creating complex animations, layouts, and styles that are both high-performing and controllable at a low level.

There are various types of Houdini APIs, each addressing different aspects of the rendering process. The main types include:

Types of Houdini APIs

Name	Description
Paint API	It allows developers to define how elements are painted on the screen.
Parser API	It allows the creation of custom properties (variables) with defined types that can be used in CSS.
Animation API	It provides more control over animations and transitions.
Typed OM API	It facilitates the manipulation of CSS values in a typed manner, providing a more performant and readable way to work with CSS values in JavaScript.
Layout API	It enables developers to size and position elements on the page.

We can use Houdini APIs in various scenarios, such as creating custom effects, implementing complex animations, and optimizing layout handling to improve the overall user experience of web applications.

Note: Keep an eye on the ‘‘Is Houdini ready yet?’’https://ishoudinireadyyet.com/ to see new features and updates being added to the Houdini APIs.

Common usage

Houdini APIs offer a notable performance boost by delegating tasks to the browser’s rendering engine. Enhancing resource efficiency for smoother animations, quicker rendering, and a more responsive user interface.

It is recommended to explore different Houdini APIs available to understand their working and various use cases. For example,

If we are a media company, we can use the CSS Paint API to create dynamic backgrounds for our articles, which will increase user engagement.
If we are an e-commerce platform, we can utilize the CSS Layout API to implement a custom grid system, improving page load times.

Let’s see some working examples to better understand the usage of the Houdini APIs.

The Paint API

The Paint API allows developers to define and control how elements are painted on the screen. For the demonstration purpose, let’s define a custom paint worklet to create a checkerboard pattern for the demonstration. To apply our custom paint worklet, we first need to check if the browser supports Houdini APIs, and then we can register it with the browser.

The following are the general steps involved in utilizing Houdini APIs effectively:

class CheckerboardPainter {
    static get inputProperties() {
        return ['--checkerboard-size', '--checkerboard-color'];
    }
    paint(ctx, size, properties) {
        let checkerSize = parseInt(properties.get('--checkerboard-size').toString()) || 20;
        const color = properties.get('--checkerboard-color').toString() || 'black';
        // Clamp checkerSize between 1 and 100
        checkerSize = Math.max(1, Math.min(checkerSize, 100));
        const rows = Math.ceil(size.height / checkerSize);
        const cols = Math.ceil(size.width / checkerSize);
        ctx.fillStyle = color;
        for (let row = 0; row < rows; row++) {
            for (let col = 0; col < cols; col++) {
                if ((row + col) % 2 === 0) {
                    ctx.fillRect(col * checkerSize, row * checkerSize, checkerSize, checkerSize);
                }
            }
        }
    }
}
registerPaint('checkerboard', CheckerboardPainter);

Code explanation

Let’s understand the CheckerboardPainter class line by line:

Lines 2–4: Define a static method inputProperties that returns an array of custom CSS properties (--checkerboard-size and --checkerboard-color) which will be used by the paint method to customize the appearance of the checkerboard.
Line 6: The paint method takes three parameters:
- ctx: This is the rendering context used to draw on the canvas.
- size: This provides the width and height of the area to be painted.
- properties: This is a CSSStyleValueMapAn interface that represents a collection of CSS property values, often used in conjunction with the Houdini Paint API. containing the custom properties defined in the inputProperties method.
Line 7: This retrieves the --checkerboard-size property, converts it to a string, and parses it as an integer. If the value is not set, it uses 20 as the default.
Line 8: This retrieves the --checkerboard-color property, and converts it to a string with a default value of black.
Line 11: This defines the range of 1 to 100 for the checkerSize.
Lines 13–14: Calculate the number of rows and columns needed to fill the height and width of the area with squares of size checkerSize.
Line 16: This sets the fill color for the rectangles that will be drawn to the color specified by the --checkerboard-color property.
Lines 18–24: The nested loops iterate over each row and column, and if the sum of the current row and column indexes is even, a filled rectangle is drawn at the calculated position and size.
Line 28: This registers the CheckerboardPainter class as a paint worklet with the name checkerboard. This allows us to use the paint(checkerboard) function in CSSThe CSS object is a global object provided by the browser that contains methods and properties related to CSS. to apply the checkerboard pattern to elements.

Now we have defined our custom logic, it is time to register our paint worklet with the browser:

This code checks if the paintWorklet property exists in the CSS object. The expression 'paintWorklet' in CSS returns true if the paintWorklet feature is supported by the browser, and false otherwise. This serves as a feature detection mechanism to ensure that the code runs only in browsers that support the CSS Paint API. If the paintWorklet feature is supported, the code executes the addModule method that loads and registers a JavaScript module (in this case, 'paintWorklet.js') as a paint worklet.

Execution

Now we have defined and registered our custom logic with the browser, let’s execute the code and see the Houdini Paint API in action.

Code explanation

Let’s understand how the browser invokes the registered behaviors during its rendering process:

Lines 7–15: We define a CSS class .example that sets the dimensions and initial custom properties (--checkerboard-size and --checkerboard-color) for a checkerboard background, using a paint worklet.
Line 22: This loads the paint.js script to register the paint worklet.
Lines 23–27: Create an event listener on an input element to dynamically update the --checkerboard-size property of the .example element based on the input value, allowing for real-time changes to the checkerboard size.

Clean-up

As the Houdini Paint API does not have a built-in method to unregister a paint worklet directly, we typically handle clean-up by removing the elements that use the custom paint worklet.

This approach ensures that the custom paint worklet is no longer applied to the element, effectively ‘cleaning up’ the custom behavior when it’s no longer needed.

Typed OM API

Let’s take a relatively simple example to help us understand how Typed OM API allows the manipulation of CSS values in a typed and efficient manner. The Typed OM API provides a set of typed JavaScript objects that correspond to CSS values, making it easier to create, read, and modify CSS directly in JavaScript. We’ll create a simple HTML file to demonstrate how to check for support and use a CSSUnitValue object to display CSS values and units.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Houdini Example</title>
  <style>
    body { font-family: Arial, sans-serif; }
  </style>
</head>
<body>
  <h1>Houdini API Demo</h1>
  <div class="example">
    <p> Using the Houdini Typed OM API for <code>CSS.px(20)</code> returns:</p>
    <p id="css-value"></p>
    <p id="css-unit"></p>
  </div>
  <script>
   if (CSS && CSS.px) {
      const value = CSS.px(20);
      document.getElementById('css-value').textContent = `Value = ${value.value}`;
      document.getElementById('css-unit').textContent = `Unit = ${value.unit}`;
    } else {
      console.log("Houdini API not supported in this environment.");
    } 
  </script>
</body>
</html>

Displaying value and unit using the Houdini Typed OM API

In the above code example, we check if the CSS Houdini API is supported by verifying the existence of CSS and CSS.px. If supported, it creates a CSSUnitValue object representing 20 pixels using CSS.px(20) and updates the text content of elements with IDs css-value and css-unit to display the value and unit of this object, respectively. If the Houdini API is not supported, it logs a message to the console indicating the lack of support.

Benefits of Houdini APIs

Houdini APIs offer several key benefits, including:

Enhanced control: It gives fine-tuned control over styling and layout with the ability to implement custom features.
Improved performance: It enables high performance by offloading certain rendering tasks to the GPU and optimizing the pipeline.
Better user experience: It enhances user experience through smooth animations, custom layouts, and faster loading times.

Limitations of Houdini APIs

While Houdini APIs offer numerous advantages, they also come with some limitations. These include:

Browser support: Not all Houdini APIs are supported across all browsers. Ensure browser support for Houdini APIs before implementing them in production applications.
Learning curve: The complexity in understanding and implementing the APIs creates a steep learning curve for developers who are not familiar with low-level programming.
Performance overheads: Improper use can lead to performance bottlenecks. Regularly test and profile your application to identify and fix performance issues.

Houdini APIs unlock exciting new possibilities for web developers to create stunning and dynamic web experiences. By getting familiar with the various Houdini APIs and understanding their lifecycle and benefits, we can experiment with code to leverage these powerful features in real-world applications to push the boundaries of web design and development.