圆弧 arc()
arc(
centerx, centery, radius,
startingAngle, endingAngle,
anticlockwise = false
)
弧 arcTo()
arcTo(
x1, y1,
x2, y2,
radius );
二次贝塞尔(Bezier) 曲线 quadraticCurveTo()
quadraticCurveTo(
x1, y1,
x2, y2 );
三次贝塞尔(Bezier) 曲线 bezierCurveTo()
bezierCurveTo(
x1, y1,
x2, y2，
x3, y3 );
