Canvas

Canvas

Canvas是HTML5新增的组件，它就像一块幕布，可以用JavaScript在上面绘制各种图表、动画等。

<canvas id="test-canvas" width="300" height="200"></canvas>
let ctx = canvas.getContext('2d');  // 绘制2D
gl = canvas.getContext("webgl");  // 绘制3D

// 绘制图形
let
    canvas = document.getElementById('test-shape-canvas'),
    ctx = canvas.getContext('2d');

ctx.clearRect(0, 0, 200, 200); // 擦除(0,0)位置大小为200x200的矩形，擦除的意思是把该区域变为透明
ctx.fillStyle = '#dddddd'; // 设置颜色
ctx.fillRect(10, 10, 130, 130); // 把(10,10)位置大小为130x130的矩形涂色
// 利用Path绘制复杂路径:
let path=new Path2D();
path.arc(75, 75, 50, 0, Math.PI*2, true);
path.moveTo(110,75);
path.arc(75, 75, 35, 0, Math.PI, false);
path.moveTo(65, 65);
path.arc(60, 65, 5, 0, Math.PI*2, true);
path.moveTo(95, 65);
path.arc(90, 65, 5, 0, Math.PI*2, true);
ctx.strokeStyle = '#0000ff';
ctx.stroke(path);

// 绘制文本
let
    canvas = document.getElementById('test-text-canvas'),
    ctx = canvas.getContext('2d');

ctx.fillStyle = '#fff';
ctx.fillRect(0, 0, 300, 100);
ctx.shadowOffsetX = 2;
ctx.shadowOffsetY = 2;
ctx.shadowBlur = 2;
ctx.shadowColor = '#ccc';
ctx.font = '28px Arial';
ctx.fillStyle = '#999';
ctx.fillText('带阴影的文字', 20, 40);