How to create animations on a canvas using requestAnimationFrame()?
Jun 22, 2025 am 12:52 AM
The key to using requestAnimationFrame() to implement smooth animation on HTML Canvas is to understand its operating mechanism and cooperate with the Canvas drawing process. 1. requestAnimationFrame() is an API designed for animation by the browser. It can be synchronized with the screen refresh rate to avoid lag or tear, and is more efficient than setTimeout or setInterval; 2. The animation infrastructure includes preparing canvas elements, obtaining context, and defining the main loop function animate(), where the canvas is cleared and the next frame is requested for continuous redrawing; 3. To achieve dynamic effects, state variables, such as the coordinates of the ball, are updated in each frame, thereby forming continuous animation; 4. To improve expression, it can be achieved by adding time control to ensure speed consistency, using double buffering technology to optimize rendering, and using easing functions to enhance the naturalness of motion. After mastering these core points, you can create a variety of animation effects through creative and detailed adjustments.
Want to use requestAnimationFrame() to make smooth animations on HTML Canvas? This is actually not difficult. The key is to understand its operating mechanism and cooperate with Canvas' drawing process.
Basic principle: Why choose requestAnimationFrame()
requestAnimationFrame() is an API designed specifically for animation by the browser. It calls the specified function before the next repaint, which ensures that the animation is synchronized with the screen refresh rate (usually 60Hz, which is 60 frames per second), thereby avoiding lag or tearing.
It is more efficient than setTimeout or setInterval because the browser can automatically optimize multiple animations, reduce resource usage, and even pause execution when the page is invisible.
Building infrastructure: Canvas and main loop
First prepare your HTML page and insert a <canvas></canvas> element:
<canvas id="myCanvas" width="800" height="600"></canvas>
Then get the context in JS and start the animation loop:
const canvas = document.getElementById('myCanvas');
const ctx = canvas.getContext('2d');
function animate() {
// Clear canvas ctx.clearRect(0, 0, canvas.width, canvas.height);
// Draw content drawSomething();
// Request the next frame requestAnimationFrame(animate);
}
animate(); // Start the first frameThe key point is to clear the canvas before each drawing, otherwise the content of the previous frame will remain. This structure is the basis of all your animation logic.
Implement dynamic effects: add state changes
To make the picture move, certain variables need to be constantly changed. For example, drawing a moving ball:
let x = 0;
function drawSomething() {
ctx.beginPath();
ctx.arc(x, 100, 10, 0, Math.PI * 2);
ctx.fillStyle = 'red';
ctx.fill();
ctx.closePath();
x = 2;
if (x > canvas.width) {
x = 0;
}
} In this example, x represents the horizontal coordinate of the ball. Update this value every frame, and then re-draw it, you can see the ball move from left to right.
If you want the animation speed to be unaffected by the frame rate, it is recommended to add time control, such as recording the start time and calculating the elapsed time difference to determine the position.
Improve expressiveness: add details to make it more natural
- Double buffering technology is not necessary, but you can consider rendering complex graphics off-screen and drawing them on the main canvas one after another.
- If you have multiple animation objects, you can save their state with an array, and update and draw them uniformly in each frame.
- Remember not to forget to stop looping at the end of the animation, although most of the time you loop infinitely.
- Using the easing function can make the movement more natural, such as slowing in and out.
For example, add a relief effect to the above ball:
let x = 0;
let velocity = 0;
function drawSomething() {
velocity = (targetX - x) * 0.1; // Simple elastic formula x = velocity;
ctx.beginPath();
ctx.arc(x, 100, 10, 0, Math.PI * 2);
ctx.fillStyle = 'red';
ctx.fill();
ctx.closePath();
}Basically that's it. As long as you master the basic structure and changes, all you have to do is to adjust the creativity and details.
The above is the detailed content of How to create animations on a canvas using requestAnimationFrame()?. For more information, please follow other related articles on the PHP Chinese website!
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