Arcs 圆弧

An arc in jCanvas is, essentially, part of the rim of a circle (similar to the smile on a smiley-face).
jCanvas中的圆弧，本质上是圆圈的一部分（就像笑脸上的笑容一样）。

Basic Usage 基本用法

You can draw an arc using the drawArc() method. The size of an arc is determined by its start, end, and radius properties.
你可以用drawArc()方法来画一个圆弧，圆弧的大小取决于它的start，end和radius属性。
jCanvas considers zero degrees to lie due north of the arc (like the 12 on an analog clock).
jCanvas把0度认为位于圆弧的正北方（像针式钟表的12点方向）

// Draw a 90° arc 画一个90度圆弧
$('canvas').drawArc({
  strokeStyle: '#000',
  strokeWidth: 5,
  x: 100, y: 100,
  radius: 50,
  // start and end angles in degrees 以角度值计算的起始及终止角
  start: 0, end: 90
});

If you omit the start and end properties, the arc defaults to a full circle.
如果你省略了start和end属性的话，圆弧默认为一个完整的圆。

// Draw a full circle  画一个完整的圆
$('canvas').drawArc({
  strokeStyle: '#000',
  strokeWidth: 5,
  x: 100, y: 100,
  radius: 50
});

Radian values 弧度值

The start and end values are measured in degrees by default. If you'd prefer to use radians, include the inDegrees property with a value of false.
start和end的值默认是以角度值衡量的，如果你喜欢使用弧度值，就再写进inDegrees属性，设置其值为false。

// Draw a black semicircle 画一个黑色的半圆
$('canvas').drawArc({
  fillStyle: 'black',
  x: 100, y: 100,
  radius: 50,
  start: 0, end: Math.PI,
  ccw: true,
  inDegrees: false
});

Closed Arc 闭合的圆弧

Using the closed property, you can also close an arc, which connects the start and end points.
使用closed属性，你可以闭合一个圆弧，会将起始点和终止点连接起来

// Draw a closed red arc 画一个闭合圆弧
$('canvas').drawArc({
  strokeStyle: '#c33',
  strokeWidth: 5,
  x: 100, y: 100,
  radius: 50,
  start: 45, end: 225,
  closed: true
});