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

css文件

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

#time-graph-canvas {
	width: 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