How to draw graphics and implement animations in HTML5? 1. Insert the
Canvas is a very practical drawing tool provided by HTML5. Although it is just a blank canvas itself, through JavaScript operations, you can use it to draw graphics, animations, and even game interfaces. The key is to understand its basic usage.
Prepare a Canvas element
First, you need to insert a <canvas></canvas> tag into the HTML. The most basic writing method is as follows:
<canvas id="myCanvas" width="500" style="max-width:90%"></canvas>
The width and height are set here. If not, the default is 300x150 pixels. Remember to add an id to it to facilitate subsequent operation using JS.
Next, get this canvas object in JavaScript and create a drawing context, which is the basis for all drawing operations:
const canvas = document.getElementById('myCanvas'); const ctx = canvas.getContext('2d');
getContext('2d') is the most common pattern, which means you are doing a two-dimensional drawing.
Draw simple shapes
With context, you can start drawing things. For example, drawing a rectangle:
ctx.fillStyle = 'blue'; // Set the fill color ctx.fillRect(50, 50, 100, 100); // Draw a 100x100 rectangle at (50, 50) position
This code draws a blue square on the canvas. If you want to draw borders instead of filling, you can use the strokeRect method.
Drawing a circle is a little more complicated, and you need to use a path:
ctx.beginPath(); ctx.arc(200, 100, 50, 0, Math.PI * 2); // The center of the circle is (200, 100), the radius is 50 ctx.fillStyle = 'red'; ctx.fill(); ctx.closePath();
Remember that it is best to call closePath() after each drawing to keep the code neat.
Add text and pictures
Canvas not only draw graphics, but also adds text and images.
Add text:
ctx.font = '20px Arial'; ctx.fillStyle = 'black'; ctx.fillText('Hello Canvas!', 10, 30);
This will show a line of black text in the upper left corner.
Draw pictures:
First prepare an image, which can be a URL local or network:
const img = new Image();
img.src = 'example.png';
img.onload = function() {
ctx.drawImage(img, 100, 100, 200, 150); // Draw the picture at the specified position and set the width and height}; Note that the image loading is asynchronous, so you must wait until onload callback is triggered before drawing.
Animation and Clear Canvas
Want to get canvas moving? Then you have to constantly repaint the canvas content. Usually, requestAnimationFrame is used to achieve smooth animation.
For example, let a circle move:
let x = 0;
function animate() {
ctx.clearRect(0, 0, canvas.width, canvas.height); // Clear the entire canvas ctx.beginPath();
ctx.arc(x, 100, 30, 0, Math.PI * 2);
ctx.fillStyle = 'green';
ctx.fill();
ctx.closePath();
x = 2;
if (x < canvas.width) {
requestAnimationFrame(animate);
}
}
animate(); The key point here is to call clearRect before each loop to clear the previous picture, otherwise the old graphics will remain on the canvas.
Basically that's it. Canvas is powerful, but it is enough to master these basic operations when you first get started. At the beginning, you may feel a bit abstract, and you can get started by trying it a few more times.
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