HTMLCanvasElement: getContext() method
======================================

 The
 **`HTMLCanvasElement.getContext()`** method returns a drawing
 context on the canvas, or `null` if the context identifier is not
 supported, or the canvas has already been set to a different context mode.

 Later calls to this method on the same canvas element, with the same
 `contextType` argument, will always return the same drawing context instance
 as was returned the first time the method was invoked. It is not possible to get a
 different drawing context object on a given canvas element.

Syntax
------


```js
getContext(contextType)
getContext(contextType, contextAttributes)
```

### Parameters

`contextType`

 A string containing the context identifier defining the drawing
 context associated to the canvas. Possible values are:


* `"2d"`, leading to the creation of a
 `CanvasRenderingContext2D` object representing a two-dimensional
 rendering context.
* `"webgl"` (or `"experimental-webgl"`) which will create a
 `WebGLRenderingContext` object representing a three-dimensional
 rendering context. This context is only available on browsers that implement WebGL version 1 (OpenGL ES 2.0).
* `"webgl2"` which will create a `WebGL2RenderingContext`
 object representing a three-dimensional rendering context. This context is only
 available on browsers that implement WebGL
 version 2 (OpenGL ES 3.0). 
Experimental
* `"webgpu"`, which will create a
 `GPUCanvasContext` object representing a three-dimensional
 rendering context for WebGPU render pipelines. This context is only available on browsers that implement The WebGPU API.
* `"bitmaprenderer"` which will create an
 `ImageBitmapRenderingContext` which only provides functionality to
 replace the content of the canvas with a given `ImageBitmap`.

**Note:** The identifier `"experimental-webgl"` is used
 in new implementations of WebGL. These implementations have either not reached
 test suite conformance, or the graphics drivers on the platform are not yet
 stable. The Khronos Group certifies WebGL
 implementations under certain conformance rules.


`contextAttributes` Optional

 You can use several context attributes when creating your rendering context, for
 example:



```js
const gl = canvas.getContext("webgl", {
  antialias: false,
  depth: false,
});
```


2d context attributes:

`alpha`

 A boolean value that indicates if the canvas
 contains an alpha channel. If set to `false`, the browser now knows
 that the backdrop is always opaque, which can speed up drawing of transparent
 content and images.


`colorSpace` Optional

Specifies the color space of the rendering context. Possible values are:

* `"srgb"` selects the sRGB color space. This is the default value.
* `"display-p3"` selects the display-p3 color space.

`desynchronized`

 A boolean value that hints the user agent
 to reduce the latency by desynchronizing the canvas paint cycle from the event
 loop


`willReadFrequently`

 A boolean value that indicates whether
 or not a lot of read-back operations are planned. This will force the use of a
 software (instead of hardware accelerated) 2D canvas and can save memory when
 calling `getImageData()`
 frequently.


WebGL context attributes:

`alpha`

 A boolean value that indicates if the canvas
 contains an alpha buffer.


`depth`

 A boolean value that indicates that the drawing
 buffer is requested to have a depth buffer of at least 16 bits.


`stencil`

 A boolean value that indicates that the drawing
 buffer is requested to have a stencil buffer of at least 8 bits.


`desynchronized`

 A boolean value that hints the user agent
 to reduce the latency by desynchronizing the canvas paint cycle from the event
 loop


`antialias`

 A boolean value that indicates whether or not
 to perform anti-aliasing if possible.


`failIfMajorPerformanceCaveat`

 A boolean value that
 indicates if a context will be created if the system performance is low or if no
 hardware GPU is available.


`powerPreference`

 A hint to the user agent
 indicating what configuration of GPU is suitable for the WebGL context. Possible
 values are:


`"default"`

 Let the user agent decide which GPU configuration is
 most suitable. This is the default value.


`"high-performance"`

 Prioritizes rendering performance over
 power consumption.


`"low-power"`

 Prioritizes power saving over rendering
 performance.



`premultipliedAlpha`

 A boolean value that indicates that
 the page compositor will assume the drawing buffer contains colors with
 pre-multiplied alpha.


`preserveDrawingBuffer`

 If the value is true the
 buffers will not be cleared and will preserve their values until cleared or
 overwritten by the author.


`xrCompatible`

 A boolean value that hints to the user agent
 to use a compatible graphics adapter for an
 immersive XR device. Setting this
 synchronous flag at context creation is discouraged; rather call the asynchronous
 `WebGLRenderingContext.makeXRCompatible()` method the moment you
 intend to start an XR session.



**Note:** The WebGPU specification does not define any specific context attributes for `getContext()`. Instead, it provides configuration options via the `GPUCanvasContext.configure()` method.

### Return value

A rendering context which is either a

* `CanvasRenderingContext2D` for `"2d"`,
* `WebGLRenderingContext` for `"webgl"` and
 `"experimental-webgl"`,
* `WebGL2RenderingContext` for `"webgl2"`
* `GPUCanvasContext` for `"webgpu"` or
* `ImageBitmapRenderingContext` for `"bitmaprenderer"`.

 If the `contextType` doesn't match a possible drawing context, or differs
 from the first `contextType` requested, `null` is returned.

Examples
--------

Given this `<canvas>` element:


```html
<canvas id="canvas" width="300" height="300"></canvas>
```


You can get a `2d` context of the canvas with the following code:


```js
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
console.log(ctx); // CanvasRenderingContext2D { /\* … \*/ }
```


Now you have the 2D rendering context for a canvas and you can draw within it.

Specifications
--------------

| Specification |
| --- |
| HTML Standard # dom-canvas-getcontext-dev |

Browser compatibility
---------------------

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See also
--------

* `HTMLCanvasElement`: Interface used to define the `HTMLCanvasElement.getContext()` method
* `OffscreenCanvas.getContext()`
* `CanvasRenderingContext2D.getContextAttributes()`, `WebGLRenderingContext.getContextAttributes()`
* `CanvasRenderingContext2D`, `ImageBitmapRenderingContext`,
 `WebGLRenderingContext`, `WebGL2RenderingContext`, `GPUCanvasContext`: Available rendering contexts
* DCI-P3 color space on Wikipedia
* sRGB color space on Wikipedia