HTML `canvas` for Dynamic Graphics and Animations
Jul 21, 2025 am 02:53 AM
Canvas is HTML5's drawing API suitable for dynamic graphics and animations. 1. It is based on pixel operation and is efficient and suitable for games and visualization; 2. When using it, you need to first obtain the context to draw graphics, such as drawing rectangles, circles, etc.; 3. Animation is achieved by clearing the canvas, updating the status, and redrawing, and using requestAnimationFrame to control the frame rate; 4. Performance optimization includes reducing the redraw area, avoiding frequent creation of objects, and using off-screen canvas; 5. Interaction is achieved by listening to events and coordinate calculations, such as click detection. Mastering these key points allows you to create smooth and efficient animations.
Canvas is a very practical drawing API provided by HTML5, which is especially suitable for dynamic graphics and animations. It is not based on DOM like SVG, but operates pixels directly on the canvas, which is efficient and is suitable for scenes such as games, data visualization, real-time animation, etc.
Basic usage: try drawing a graphic first
The first step in using canvas is to get the context and draw the content through this context. The most common one is the 2D rendering context.
<canvas id="myCanvas" width="400" height="300"></canvas> <script> const canvas = document.getElementById('myCanvas'); const ctx = canvas.getContext('2d'); ctx.fillStyle = 'red'; ctx.fillRect(50, 50, 100, 100); </script>
The above code is to draw a red rectangle on the canvas. It looks simple, but that's the basis for all complex graphics. You can draw lines, circles, text, pictures, and even path combinations.
One thing to note is that canvas is a "forget it after drawing" pattern, and there is no object model. Once you finish drawing a graphic, it blends with the background, unless you record the state yourself and re-draw it.
Principle of animation implementation: Continuously repaint the picture
The essence of canvas animation is to continuously clear the canvas, update the status, and re-draw. Usually we use requestAnimationFrame to drive the animation loop.
For example, make a simple moving ball:
let x = 0;
function animate() {
ctx.clearRect(0, 0, canvas.width, canvas.height); // Clear canvas ctx.beginPath();
ctx.arc(x, 150, 20, 0, Math.PI * 2);
ctx.fillStyle = 'blue';
ctx.fill();
x = 2;
if (x > canvas.width) x = 0;
requestAnimationFrame(animate);
}
animate();This example is simple, but it shows the basic structure of the animation:
- Clear the canvas
- Update location or status
- Repaint
- Call yourself to continue with the next frame
This allows for smooth animation effects.
Performance optimization: Don't let animations get stuck
Canvas animations can easily affect performance if they are not handled properly, especially in complex scenarios. Here are some common suggestions:
- Reduce redrawing area : If you only change a part, you can just clear that piece, not the entire canvas.
- Avoid frequent creation of objects : for example, do not create new paths or style objects in each frame, and prepare in advance.
- Use off-screen canvas reasonably : draw static content on a hidden canvas first, and then copy it to the main canvas to improve efficiency.
- Control frame rate : Not all animations require 60 frames per second, and proper throttling can save resources.
For example: If you want to draw many fixed background elements, you can first draw them on an off-screen canvas when initializing, and then just draw it as an image to the main canvas.
Interactive support: Click and drag can be done
Although canvas itself does not support event binding, you can interact by listening to the mouse or touching events and combining coordinate judgment.
For example, to detect whether a circular area has been clicked:
canvas.addEventListener('click', function(e) {
const rect = canvas.getBoundingClientRect();
const mouseX = e.clientX - rect.left;
const mouseY = e.clientY - rect.top;
const dx = mouseX - x;
const dy = mouseY - y;
const distance = Math.sqrt(dx*dx dy*dy);
if (distance < radius) {
console.log('Clicked!');
}
});This idea can also be extended to more complex interactions such as buttons, drag and drop, and zoom.
Basically that's it. Canvas is not particularly difficult, but to create smooth and efficient animations, you still need to pay more attention to details, especially performance and structural design.
The above is the detailed content of HTML `canvas` for Dynamic Graphics and Animations. For more information, please follow other related articles on the PHP Chinese website!
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