增強您的 Web 動畫：像專業人士一樣最佳化 requestAnimationFrame

Smooth and performant animations are essential in modern web applications. However, managing them improperly can overload the browser’s main thread, causing poor performance and janky animations. requestAnimationFrame (rAF) is a browser API designed to sync animations with the display's refresh rate, ensuring smoother motion compared to alternatives like setTimeout. But using rAF efficiently requires careful planning, especially when handling multiple animations.

In this article, we will explore how to optimize requestAnimationFrame by centralizing animation management, introducing FPS control, and keeping the browser’s main thread responsive.

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Understanding FPS and Why It Matters

Frames per second (FPS) is crucial when discussing animation performance. Most screens refresh at 60 FPS, meaning that requestAnimationFrame is called 60 times per second. To maintain smooth animations, the browser must complete its work within about 16.67 milliseconds per frame.

If too many tasks run during a single frame, the browser might miss its target frame time, causing stuttering or dropped frames. Lowering the FPS for certain animations can help reduce the load on the main thread, providing a balance between performance and smoothness.

Centralized Animation Manager with FPS Control for Better Performance

To manage animations more efficiently, we can centralize their handling with a shared loop rather than having multiple requestAnimationFrame calls scattered throughout the code. A centralized approach minimizes redundant calls and makes it easier to add FPS control.

The following AnimationManager class allows us to register and unregister animation tasks while controlling the target FPS. By default, we aim for 60 FPS, but this can be adjusted for performance needs.

class AnimationManager {
  private tasks: Set<FrameRequestCallback> = new Set();
  private fps: number = 60; // Target FPS
  private lastFrameTime: number = performance.now();
  private animationId: number | null = null; // Store the animation frame ID

  private run = (currentTime: number) => {
    const deltaTime = currentTime - this.lastFrameTime;

    // Ensure the tasks only run if enough time has passed to meet the target FPS
    if (deltaTime > 1000 / this.fps) {
      this.tasks.forEach((task) => task(currentTime));
      this.lastFrameTime = currentTime;
    }

    this.animationId = requestAnimationFrame(this.run);
  };

  public registerTask(task: FrameRequestCallback) {
    this.tasks.add(task);
    if (this.tasks.size === 1) {
      this.animationId = requestAnimationFrame(this.run); // Start the loop if this is the first task
    }
  }

  public unregisterTask(task: FrameRequestCallback) {
    this.tasks.delete(task);
    if (this.tasks.size === 0 && this.animationId !== null) {
      cancelAnimationFrame(this.animationId); // Stop the loop if no tasks remain
      this.animationId = null; // Reset the ID
    }
  }
}

export const animationManager = new AnimationManager();

In this setup, we calculate the deltaTime between frames to determine if enough time has passed for the next update based on the target FPS. This allows us to throttle the frequency of updates to ensure the browser’s main thread isn’t overloaded.

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Practical Example: Animating Multiple Elements with Different Properties

Let’s create an example where we animate three boxes, each with a different animation: one scales, another changes color, and the third rotates.

Here’s the HTML:

<div id="animate-box-1" class="animated-box"></div>
<div id="animate-box-2" class="animated-box"></div>
<div id="animate-box-3" class="animated-box"></div>

Here’s the CSS:

.animated-box {
  width: 100px;
  height: 100px;
  background-color: #3498db;
  transition: transform 0.1s ease;
}

Now, we’ll add JavaScript to animate each box with a different property. One will scale, another will change its color, and the third will rotate.

Step 1: Adding Linear Interpolation (lerp)

Linear interpolation (lerp) is a common technique used in animations to smoothly transition between two values. It helps create a gradual and smooth progression, making it ideal for scaling, moving, or changing properties over time. The function takes three parameters: a starting value, an ending value, and a normalized time (t), which determines how far along the transition is.

function lerp(start: number, end: number, t: number): number {
  return start + (end - start) * t;
}

Step 2: Scaling Animation

We start by creating a function to animate the scaling of the first box:

function animateScale(
  scaleBox: HTMLDivElement,
  startScale: number,
  endScale: number,
  speed: number
) {
  let scaleT = 0;

  function scale() {
    scaleT += speed;
    if (scaleT > 1) scaleT = 1;

    const currentScale = lerp(startScale, endScale, scaleT);
    scaleBox.style.transform = `scale(${currentScale})`;

    if (scaleT === 1) {
      animationManager.unregisterTask(scale);
    }
  }

  animationManager.registerTask(scale);
}

Step 3: Color Animation

Next, we animate the color change of the second box:

function animateColor(
  colorBox: HTMLDivElement,
  startColor: number,
  endColor: number,
  speed: number
) {
  let colorT = 0;

  function color() {
    colorT += speed;
    if (colorT > 1) colorT = 1;

    const currentColor = Math.floor(lerp(startColor, endColor, colorT));
    colorBox.style.backgroundColor = `rgb(${currentColor}, 100, 100)`;

    if (colorT === 1) {
      animationManager.unregisterTask(color);
    }
  }

  animationManager.registerTask(color);
}

Step 4: Rotation Animation

Finally, we create the function to rotate the third box:

function animateRotation(
  rotateBox: HTMLDivElement,
  startRotation: number,
  endRotation: number,
  speed: number
) {
  let rotationT = 0;

  function rotate() {
    rotationT += speed; // Increment progress
    if (rotationT > 1) rotationT = 1;

    const currentRotation = lerp(startRotation, endRotation, rotationT);
    rotateBox.style.transform = `rotate(${currentRotation}deg)`;

    // Unregister task once the animation completes
    if (rotationT === 1) {
      animationManager.unregisterTask(rotate);
    }
  }

  animationManager.registerTask(rotate);
}

Step 5: Starting the Animations

Finally, we can start the animations for all three boxes:

// Selecting the elements
const scaleBox = document.querySelector("#animate-box-1") as HTMLDivElement;
const colorBox = document.querySelector("#animate-box-2") as HTMLDivElement;
const rotateBox = document.querySelector("#animate-box-3") as HTMLDivElement;

// Starting the animations
animateScale(scaleBox, 1, 1.5, 0.02); // Scaling animation
animateColor(colorBox, 0, 255, 0.01); // Color change animation
animateRotation(rotateBox, 360, 1, 0.005); // Rotation animation

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Note on the Main Thread

When using requestAnimationFrame, it’s essential to keep in mind that animations run on the browser’s main thread. Overloading the main thread with too many tasks can cause the browser to miss animation frames, resulting in stuttering. This is why optimizing your animations with tools like a centralized animation manager and FPS control can help maintain smoothness, even with multiple animations.

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Conclusion

Managing animations efficiently in JavaScript requires more than just using requestAnimationFrame. By centralizing animations and controlling the FPS, you can ensure smoother, more performant animations while keeping the main thread responsive. In this example, we showed how to handle multiple animations with a single AnimationManager, demonstrating how to optimize for both performance and usability. While we focused on maintaining a consistent FPS for simplicity, this approach can be expanded to handle different FPS values for various animations, though that was beyond the scope of this article.

Github 儲存庫： https://github.com/JBassx/rAF-optimization
StackBlitz： https://stackblitz.com/~/github.com/JBassx/rAF-optimization

領英： https://www.linkedin.com/in/josephciullo/

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