canvas填充规则

const canvas = document.getElementById('canvas');const ctx = canvas.getContext('2d');ctx.beginPath(); ctx.fillStyle='green'ctx.arc(50, 50, 30, 0, Math.PI * 2, true);ctx.arc(50, 50, 20, 0, Math.PI * 2, true);ctx.arc(50, 50, 15, 0, Math.PI * 2, true);ctx.arc(50, 50, 10, 0, Math.PI * 2, true);ctx.fill('evenodd');