canvas 绘制动态圆环进度条

由于使用的是vue开发，所以就展示一下绘制函数好了，上图是效果图

drawMain(drawing_elem, percent, forecolor, bgcolor) {
/*
@drawing_elem: 绘制对象
@percent：绘制圆环百分比, 范围[0, 100]
@forecolor: 绘制圆环的前景色，颜色代码
@bgcolor: 绘制圆环的背景色，颜色代码
*/
var context = drawing_elem.getContext("2d");
var center_x = drawing_elem.width / 2;
var center_y = drawing_elem.height / 2;
var rad = Math.PI*2/100;
var speed = 0;

// 绘制背景圆圈
function backgroundCircle(){
context.save();
context.beginPath();
context.lineWidth = 8; //设置线宽
var radius = center_x - context.lineWidth;
context.lineCap = "round";
context.strokeStyle = bgcolor;
context.arc(center_x, center_y, radius, 0, Math.PI*2, false);
context.stroke();
context.closePath();
context.restore();
}

//绘制运动圆环
function foregroundCircle(n){
context.save();
context.strokeStyle = forecolor;
context.lineWidth = 8;
context.lineCap = "round";
var radius = center_x - context.lineWidth;
context.beginPath();
context.arc(center_x, center_y, radius , -Math.PI/2, -Math.PI/2 +n*rad, false); //用于绘制圆弧context.arc(x坐标，y坐标，半径，起始角度，终止角度，顺时针/逆时针)
context.stroke();
context.closePath();
context.restore();
}

//绘制文字
function text(n){
context.save(); //save和restore可以保证样式属性只运用于该段canvas元素
context.fillStyle = forecolor;
var font_size = 40;
context.font = font_size + "px Helvetica";
var text_width = context.measureText(n.toFixed(0)+"%").width;
context.fillText(n.toFixed(0)+"%", center_x-text_width/2, center_y + font_size/2);
context.restore();
}

//执行动画
(function drawFrame(){
window.requestAnimationFrame(drawFrame);
context.clearRect(0, 0, drawing_elem.width, drawing_elem.height);
backgroundCircle();
text(speed);
foregroundCircle(speed);
if(speed >= percent) return;
speed += 1;
}());
},

调用的话

var time_canvas = document.getElementById("time-graph-canvas");
this.drawMain(time_canvas, 70, "#85d824", "#eef7e4");

var weather_canvas = document.getElementById("weather-graph-canvas");
this.drawMain(weather_canvas, 90, "#2ba0fb", "#e5f1fa");

html文件
<div class="time-graph">
<canvas id="time-graph-canvas" width="160" height="160"></canvas>
</div>

css文件
.time-graph {
padding-top: 20px;
display:flex;
display:-webkit-flex;
justify-content: center;
align-items: center;
}

#time-graph-canvas {
80px;
height: 80px;
}

有些绘制细节需要注意，为了保证绘制的清晰度，canvas的大小需要设置为canvas父元素大小的2倍。

其他的代码都有详细的注释，自己拷一下，运行一下就知道
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转自：本文为CSDN博主「前端小白的江湖路」的原创文章https://blog.csdn.net/qq_21058391/article/details/76691047