CanvasRenderingContext2D.createRadialGradient() - Web APIs 编辑

The CanvasRenderingContext2D.createRadialGradient() method of the Canvas 2D API creates a radial gradient using the size and coordinates of two circles.

This method returns a CanvasGradient. To be applied to a shape, the gradient must first be assigned to the fillStyle or strokeStyle properties.

Note: Gradient coordinates are global, i.e., relative to the current coordinate space. When applied to a shape, the coordinates are NOT relative to the shape's coordinates.

Syntax

CanvasGradient ctx.createRadialGradient(x0, y0, r0, x1, y1, r1);

The createRadialGradient() method is specified by six parameters, three defining the gradient's start circle, and three defining the end circle.

Parameters

x0

The x-axis coordinate of the start circle.

y0

The y-axis coordinate of the start circle.

r0

The radius of the start circle. Must be non-negative and finite.

x1

The x-axis coordinate of the end circle.

y1

The y-axis coordinate of the end circle.

r1

The radius of the end circle. Must be non-negative and finite.

Return value

CanvasGradient

A radial CanvasGradient initialized with the two specified circles.

Examples

Filling a rectangle with a radial gradient

This example initializes a radial gradient using the createRadialGradient() method. Three color stops between the gradient's two circles are then created. Finally, the gradient is assigned to the canvas context, and is rendered to a filled rectangle.

HTML

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

JavaScript

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

// Create a radial gradient
// The inner circle is at x=110, y=90, with radius=30
// The outer circle is at x=100, y=100, with radius=70
var gradient = ctx.createRadialGradient(110,90,30, 100,100,70);

// Add three color stops
gradient.addColorStop(0, 'pink');
gradient.addColorStop(.9, 'white');
gradient.addColorStop(1, 'green');

// Set the fill style and draw a rectangle
ctx.fillStyle = gradient;
ctx.fillRect(20, 20, 160, 160);

Result

Specifications

Browser compatibility

BCD tables only load in the browser

Gecko-specific notes

• Starting with Gecko 2.0 (Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1), specifying non-finite values now throws NOT_SUPPORTED_ERR instead of SYNTAX_ERR.
• Starting with Gecko 5.0 (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2), specifying a negative radius correctly throws INDEX_SIZE_ERR.

See also

• The interface defining this method: CanvasRenderingContext2D
• CanvasRenderingContext2D.createLinearGradient()