09. 贝塞尔曲线

示意图：

二次贝塞尔曲线

语法：quadraticCurveTo(cp1x, cp1y, x, y)

绘制二次贝塞尔曲线，cp1x,cp1y为一个控制点，x,y为结束点。

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
// 二次贝塞尔曲线
ctx.beginPath();
ctx.moveTo(75, 25);
ctx.quadraticCurveTo(25, 25, 25, 62.5);
ctx.quadraticCurveTo(25, 100, 50, 100);
ctx.quadraticCurveTo(50, 120, 30, 125);
ctx.quadraticCurveTo(60, 120, 65, 100);
ctx.quadraticCurveTo(125, 100, 125, 62.5);
ctx.quadraticCurveTo(125, 25, 75, 25);
ctx.stroke();

三次贝塞尔曲线

语法：bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y)

绘制三次贝塞尔曲线，cp1x,cp1y为控制点一，cp2x,cp2y为控制点二，x,y为结束点。

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
//三次贝塞尔曲线
ctx.beginPath();
ctx.moveTo(75, 40);
ctx.bezierCurveTo(75, 37, 70, 25, 50, 25);
ctx.bezierCurveTo(20, 25, 20, 62.5, 20, 62.5);
ctx.bezierCurveTo(20, 80, 40, 102, 75, 120);
ctx.bezierCurveTo(110, 102, 130, 80, 130, 62.5);
ctx.bezierCurveTo(130, 62.5, 130, 25, 100, 25);
ctx.bezierCurveTo(85, 25, 75, 37, 75, 40);
ctx.fill();