OffscreenCanvasRenderingContext2D

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨March 2023⁩.

* Some parts of this feature may have varying levels of support.

Note: This feature is available inWeb Workers.

TheOffscreenCanvasRenderingContext2D interface is aCanvasRenderingContext2D rendering context for drawing to the bitmap of anOffscreenCanvas object.It is similar to theCanvasRenderingContext2D object, with the following differences:

there is no support for user-interface features (drawFocusIfNeeded)
itscanvas attribute refers to anOffscreenCanvas object rather than a<canvas> element
the bitmap for the placeholder<canvas> element belonging to theOffscreenCanvas object is updated during the rendering update of theWindow orWorker that owns theOffscreenCanvas

Example

The following code snippet creates aWorker object using theWorker() constructor.ThetransferControlToOffscreen() method is used to get anOffscreenCanvas object from the<canvas> element so it can be transferred to the worker:

const canvas = document.getElementById("canvas");const offscreen = canvas.transferControlToOffscreen();const worker = new Worker("worker.js");worker.postMessage({ canvas: offscreen }, [offscreen]);

In the worker thread, we can use theOffscreenCanvasRenderingContext2D to draw to the bitmap of theOffscreenCanvas object:

onmessage = (event) => {  const canvas = event.data.canvas;  const offCtx = canvas.getContext("2d");  // draw to the offscreen canvas context  offCtx.fillStyle = "red";  offCtx.fillRect(0, 0, 100, 100);};

For a full example, see ourOffscreenCanvas worker example (run OffscreenCanvas worker).

Additional methods

The following method is new to theOffscreenCanvasRenderingContext2D interface and does not exist in theCanvasRenderingContext2D interface:

commit()Deprecated Non-standard: Pushes the rendered image to the context'sOffscreenCanvas object's placeholder <canvas> element.

Unsupported features

The following user interface method isnot supported by theOffscreenCanvasRenderingContext2D interface:

CanvasRenderingContext2D.drawFocusIfNeeded(): If a given element is focused, this method draws a focus ring around the current path.

Inherited properties and methods

The following properties and methods are inherited fromCanvasRenderingContext2D. They have the same usage as inCanvasRenderingContext2D

Context

CanvasRenderingContext2D.getContextAttributes()Experimental: Returns an object containing the actual context attributes. Context attributes can be requested with OffscreenCanvas.getContext().
CanvasRenderingContext2D.isContextLost(): Returnstrue if the rendering context was lost.

Drawing rectangles

CanvasRenderingContext2D.clearRect(): Sets all pixels in the rectangle defined by starting point(x, y) and size(width, height) to transparent black, erasing any previously drawn content.
CanvasRenderingContext2D.fillRect(): Draws a filled rectangle at(x, y) position whose size is determined bywidth andheight.
CanvasRenderingContext2D.strokeRect(): Paints a rectangle which has a starting point at(x, y) and has aw width and anh height onto the canvas, using the current stroke style.

Drawing text

The following methods and properties control drawing text. See also theTextMetrics object for text properties.

CanvasRenderingContext2D.fillText(): Draws (fills) a given text at the given (x, y) position.
CanvasRenderingContext2D.strokeText(): Draws (strokes) a given text at the given (x, y) position.
CanvasRenderingContext2D.measureText(): Returns aTextMetrics object.
CanvasRenderingContext2D.textRendering: Text rendering. Possible values:auto (default),optimizeSpeed,optimizeLegibility,

Line styles

The following methods and properties control how lines are drawn.

CanvasRenderingContext2D.lineWidth: Width of lines. Default1.0.
CanvasRenderingContext2D.lineCap: Type of endings on the end of lines. Possible values:butt (default),round,square.
CanvasRenderingContext2D.lineJoin: Defines the type of corners where two lines meet. Possible values:round,bevel,miter (default).
CanvasRenderingContext2D.miterLimit: Miter limit ratio. Default10.
CanvasRenderingContext2D.getLineDash(): Returns the current line dash pattern array containing an even number of non-negative numbers.
CanvasRenderingContext2D.setLineDash(): Sets the current line dash pattern.
CanvasRenderingContext2D.lineDashOffset: Specifies where to start a dash array on a line.

Text styles

The following properties control how text is laid out.

CanvasRenderingContext2D.font: Font setting. Default value10px sans-serif.
CanvasRenderingContext2D.textAlign: Text alignment setting. Possible values:start (default),end,left,right,center.
CanvasRenderingContext2D.textBaseline: Baseline alignment setting. Possible values:top,hanging,middle,alphabetic (default),ideographic,bottom.
CanvasRenderingContext2D.direction: Directionality. Possible values:ltr,rtl,inherit (default).
CanvasRenderingContext2D.letterSpacing: Letter spacing. Default:0px.
CanvasRenderingContext2D.fontKerning: Font kerning. Possible values:auto (default),normal,none.
CanvasRenderingContext2D.fontStretch: Font stretch. Possible values:ultra-condensed,extra-condensed,condensed,semi-condensed,normal (default),semi-expanded,expanded,extra-expanded,ultra-expanded.
CanvasRenderingContext2D.fontVariantCaps: Font variant caps. Possible values:normal (default),small-caps,all-small-caps,petite-caps,all-petite-caps,unicase,titling-caps.
CanvasRenderingContext2D.textRenderingExperimental: Text rendering. Possible values:auto (default),optimizeSpeed,optimizeLegibility,geometricPrecision.
CanvasRenderingContext2D.wordSpacing: Word spacing. Default value:0px
CanvasRenderingContext2D.langExperimental: Gets or sets the language of the canvas drawing context.

Fill and stroke styles

Fill styling is used for colors and styles inside shapes and stroke styling is used for the lines around shapes.

CanvasRenderingContext2D.fillStyle: Color or style to use inside shapes. Default toblack.
CanvasRenderingContext2D.strokeStyle: Color or style to use for the lines around shapes. Default toblack.

Gradients and patterns

CanvasRenderingContext2D.createConicGradient(): Creates a conic gradient around a point given by coordinates represented by the parameters.
CanvasRenderingContext2D.createLinearGradient(): Creates a linear gradient along the line given by the coordinates represented by the parameters.
CanvasRenderingContext2D.createRadialGradient(): Creates a radial gradient given by the coordinates of the two circles represented by the parameters.
CanvasRenderingContext2D.createPattern(): Creates a pattern using the specified image. It repeats the source in the directions specified by the repetition argument. This method returns aCanvasPattern.

Shadows

CanvasRenderingContext2D.shadowBlur: Specifies the blurring effect. Default:0.
CanvasRenderingContext2D.shadowColor: Color of the shadow. Default: fully-transparent black.
CanvasRenderingContext2D.shadowOffsetX: Horizontal distance the shadow will be offset. Default:0.
CanvasRenderingContext2D.shadowOffsetY: Vertical distance the shadow will be offset. Default:0.

Paths

The following methods can be used to manipulate paths of objects.

CanvasRenderingContext2D.beginPath(): Starts a new path by emptying the list of sub-paths. Call this method when you want to create a new path.
CanvasRenderingContext2D.closePath(): Causes the point of the pen to move back to the start of the current sub-path. It tries to draw a straight line from the current point to the start. If the shape has already been closed or has only one point, this function does nothing.
CanvasRenderingContext2D.moveTo(): Moves the starting point of a new sub-path to the (x, y) coordinates.
CanvasRenderingContext2D.lineTo(): Connects the last point in the current sub-path to the specified (x, y) coordinates with a straight line.
CanvasRenderingContext2D.bezierCurveTo(): Adds a cubic Bézier curve to the current path.
CanvasRenderingContext2D.quadraticCurveTo(): Adds a quadratic Bézier curve to the current path.
CanvasRenderingContext2D.arc(): Adds a circular arc to the current path.
CanvasRenderingContext2D.arcTo(): Adds an arc to the current path with the given control points and radius, connected to the previous point by a straight line.
CanvasRenderingContext2D.ellipse(): Adds an elliptical arc to the current path.
CanvasRenderingContext2D.rect(): Creates a path for a rectangle at position (x, y) with a size that is determined bywidth andheight.
CanvasRenderingContext2D.roundRect(): Creates a path for a rectangle with rounded corners at position (x, y) with a size that is determined bywidth andheight and radii determined byradii.

Drawing paths

CanvasRenderingContext2D.fill(): Fills the current sub-paths with the current fill style.
CanvasRenderingContext2D.stroke(): Strokes the current sub-paths with the current stroke style.
CanvasRenderingContext2D.clip(): Creates a clipping path from the current sub-paths. Everything drawn afterclip() is called appears inside the clipping path only. For an example, seeClipping paths in the Canvas tutorial.
CanvasRenderingContext2D.isPointInPath(): Reports whether or not the specified point is contained in the current path.
CanvasRenderingContext2D.isPointInStroke(): Reports whether or not the specified point is inside the area contained by the stroking of a path.

Transformations

Objects in theCanvasRenderingContext2D rendering context have a current transformation matrix and methods to manipulate it. The transformation matrix is applied when creating the current default path, painting text, shapes andPath2D objects. The methods listed below remain for historical and compatibility reasons asDOMMatrix objects are used in most parts of the API nowadays and will be used in the future instead.

CanvasRenderingContext2D.getTransform(): Retrieves the current transformation matrix being applied to the context.
CanvasRenderingContext2D.rotate(): Adds a rotation to the transformation matrix. The angle argument represents a clockwise rotation angle and is expressed in radians.
CanvasRenderingContext2D.scale(): Adds a scaling transformation to the canvas units by x horizontally and by y vertically.
CanvasRenderingContext2D.translate(): Adds a translation transformation by moving the canvas and its origin x horizontally and y vertically on the grid.
CanvasRenderingContext2D.transform(): Multiplies the current transformation matrix with the matrix described by its arguments.
CanvasRenderingContext2D.setTransform(): Resets the current transform to the identity matrix, and then invokes thetransform() method with the same arguments.
CanvasRenderingContext2D.resetTransform(): Resets the current transform by the identity matrix.

Compositing

CanvasRenderingContext2D.globalAlpha: Alpha value that is applied to shapes and images before they are composited onto the canvas. Default1.0 (opaque).
CanvasRenderingContext2D.globalCompositeOperation: WithglobalAlpha applied this sets how shapes and images are drawn onto the existing bitmap.

Drawing images

CanvasRenderingContext2D.drawImage(): Draws the specified image. This method is available in multiple formats, providing a great deal of flexibility in its use.

Pixel manipulation

Image smoothing

CanvasRenderingContext2D.imageSmoothingEnabled: Image smoothing mode; if disabled, images will not be smoothed if scaled.
CanvasRenderingContext2D.imageSmoothingQuality: Allows you to set the quality of image smoothing.

The canvas state

TheCanvasRenderingContext2D rendering context contains a variety of drawing style states (attributes for line styles, fill styles, shadow styles, text styles). The following methods help you to work with that state:

CanvasRenderingContext2D.save(): Saves the current drawing style state using a stack so you can revert any change you make to it usingrestore().
CanvasRenderingContext2D.restore(): Restores the drawing style state to the last element on the 'state stack' saved bysave().
CanvasRenderingContext2D.canvas: A read-only reference to anOffscreenCanvas object.
CanvasRenderingContext2D.getContextAttributes()Experimental: Returns an object containing the actual context attributes. Context attributes can be requested with HTMLCanvasElement.getContext().
CanvasRenderingContext2D.reset(): Resets the current drawing style state to the default values.

Filters

CanvasRenderingContext2D.filter: Applies a CSS or SVG filter to the canvas; e.g., to change its brightness or blurriness.

Unsupported properties and methods

The following method isnot supported in theOffscreenCanvasRenderingContext2D interface:

CanvasRenderingContext2D.drawFocusIfNeeded(): If a given element is focused, this method draws a focus ring around the current path.

Specifications

Specification
HTML # the-offscreen-2d-rendering-context

Browser compatibility

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This page was last modified on⁨Aug 12, 2025⁩ byMDN contributors.

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