CanvasRenderingContext2D.ellipse() - Web APIs 编辑

The CanvasRenderingContext2D.ellipse() method of the Canvas 2D API adds an elliptical arc to the current sub-path.

Syntax

void ctx.ellipse(x, y, radiusX, radiusY, rotation, startAngle, endAngle [, anticlockwise]);

The ellipse() method creates an elliptical arc centered at (x, y) with the radii radiusX and radiusY. The path starts at startAngle and ends at endAngle, and travels in the direction given by anticlockwise (defaulting to clockwise).

Parameters

x

The x-axis (horizontal) coordinate of the ellipse's center.

y

The y-axis (vertical) coordinate of the ellipse's center.

radiusX

The ellipse's major-axis radius. Must be non-negative.

radiusY

The ellipse's minor-axis radius. Must be non-negative.

rotation

The rotation of the ellipse, expressed in radians.

startAngle

The angle at which the ellipse starts, measured clockwise from the positive x-axis and expressed in radians.

endAngle

The angle at which the ellipse ends, measured clockwise from the positive x-axis and expressed in radians.

anticlockwise Optional

An optional Boolean which, if true, draws the ellipse anticlockwise (counter-clockwise). The default value is false (clockwise).

Examples

Drawing a full ellipse

This example draws an ellipse at an angle of π/4 radians (45°). To make a full ellipse, the arc begins at an angle of 0 radians (0°), and ends at an angle of 2π radians (360°).

HTML

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

JavaScript

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

// Draw the ellipse
ctx.beginPath();
ctx.ellipse(100, 100, 50, 75, Math.PI / 4, 0, 2 * Math.PI);
ctx.stroke();

// Draw the ellipse's line of reflection
ctx.beginPath();
ctx.setLineDash([5, 5]);
ctx.moveTo(0, 200);
ctx.lineTo(200, 0);
ctx.stroke();

Result

Various elliptical arcs

This example creates three elliptical paths with varying properties.

HTML

<canvas id="canvas"></canvas>

JavaScript

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

ctx.fillStyle = 'red';
ctx.beginPath();
ctx.ellipse(60, 75, 50, 30, Math.PI * .25, 0, Math.PI * 1.5);
ctx.fill();

ctx.fillStyle = 'blue';
ctx.beginPath();
ctx.ellipse(150, 75, 50, 30, Math.PI * .25, 0, Math.PI);
ctx.fill();

ctx.fillStyle = 'green';
ctx.beginPath();
ctx.ellipse(240, 75, 50, 30, Math.PI * .25, 0, Math.PI, true);
ctx.fill();

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The interface defining this method: CanvasRenderingContext2D
• Use CanvasRenderingContext2D.arc() to draw a circular arc