javascript - 如何优化视网膜设备的画布圈？

Question

请告诉我如何使视网膜设备的画布看起来清晰？如果您在我的示例中展示，我将不胜感激 -小提琴

var canvas = document.getElementById('timer');
var context = canvas.getContext('2d');
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 105;
var endPercent = 100;
var curPerc = 0;
var counterClockwise = false;
var circ = Math.PI * 2;
var quart = Math.PI / 2;