1.绘制圆的角度示意图：

2 倒计时中，时钟数字的渲染逻辑：

3 直线边缘样式的设置

context.lineCap = “butt”;

context.lineCap = “round”;

context.lineCap = “square”;

如何把canvas元素作为网站背景

1. 最简单的做法是绝对定位并且z-index属性设置为负数。

2. 使用 Canvas 绘制背景图

https://imququ.com/post/use-canvas-as-background-image.html?utm_source=tuicool&utm_medium=referral

<div style="200px;height:200px;" id="cloud">红心是我的背景图！</div>    
<canvas style="display:none;" id="can" width="200" height="200"></canvas>
<script>
(function() {
    var canvas = document.getElementById('can'), context;

    if(!canvas.getContext) {
        alert('你的浏览器不支持 canvas!');
        return;
    }

    context = canvas.getContext('2d');
    context.fillStyle = 'red';
    context.beginPath();
    context.moveTo(75,40);
    context.bezierCurveTo(75,37,70,25,50,25);
    context.bezierCurveTo(20,25,20,62.5,20,62.5);
    context.bezierCurveTo(20,80,40,102,75,120);
    context.bezierCurveTo(110,102,130,80,130,62.5);
    context.bezierCurveTo(130,62.5,130,25,100,25);
    context.bezierCurveTo(85,25,75,37,75,40);
    context.fill();

    document.getElementById('cloud').style.backgroundImage = 'url("' + context.canvas.toDataURL() + '")';
})();
</script>