CanvasRenderingContext2D.arc() - Web APIs 编辑

The CanvasRenderingContext2D.arc() method of the Canvas 2D API adds a circular arc to the current sub-path.

Syntax

void ctx.arc(x, y, radius, startAngle, endAngle [, anticlockwise]);

The arc() method creates a circular arc centered at (x, y) with a radius of radius. The path starts at startAngle, ends at endAngle, and travels in the direction given by anticlockwise (defaulting to clockwise).

Parameters

x

The horizontal coordinate of the arc's center.

y

The vertical coordinate of the arc's center.

radius

The arc's radius. Must be positive.

startAngle

The angle at which the arc starts in radians, measured from the positive x-axis.

endAngle

The angle at which the arc ends in radians, measured from the positive x-axis.

anticlockwise Optional

An optional Boolean. If true, draws the arc counter-clockwise between the start and end angles. The default is false (clockwise).

Examples

Drawing a full circle

This example draws a complete circle with the arc() method.

HTML

<canvas></canvas>

JavaScript

The arc is given an x-coordinate of 100, a y-coordinate of 75, and a radius of 50. To make a full circle, the arc begins at an angle of 0 radians (0°), and ends at an angle of 2π radians (360°).

const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');

ctx.beginPath();
ctx.arc(100, 75, 50, 0, 2 * Math.PI);
ctx.stroke();

Result

Different shapes demonstrated

This example draws various shapes to show what is possible with arc().

HTML

<canvas width="150" height="200"></canvas>

JavaScript

const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');

// Draw shapes
for (let i = 0; i <= 3; i++) {
  for (let j = 0; j <= 2; j++) {
    ctx.beginPath();
    let x             = 25 + j * 50;                 // x coordinate
    let y             = 25 + i * 50;                 // y coordinate
    let radius        = 20;                          // Arc radius
    let startAngle    = 0;                           // Starting point on circle
    let endAngle      = Math.PI + (Math.PI * j) / 2; // End point on circle
    let anticlockwise = i % 2 == 1;                  // Draw anticlockwise

    ctx.arc(x, y, radius, startAngle, endAngle, anticlockwise);

    if (i > 1) {
      ctx.fill();
    } else {
      ctx.stroke();
    }
  }
}

Result

Screenshot	Live sample

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The interface defining this method: CanvasRenderingContext2D
• Use CanvasRenderingContext2D.ellipse() to draw an elliptical arc.