CanvasRenderingContext2D.drawImage() - Web APIs 编辑

The CanvasRenderingContext2D.drawImage() method of the Canvas 2D API provides different ways to draw an image onto the canvas.

Syntax

void ctx.drawImage(image, dx, dy);
void ctx.drawImage(image, dx, dy, dWidth, dHeight);
void ctx.drawImage(image, sx, sy, sWidth, sHeight, dx, dy, dWidth, dHeight);

Parameters

image

An element to draw into the context. The specification permits any canvas image source (CanvasImageSource), specifically, a CSSImageValue, an HTMLImageElement, an SVGImageElement, an HTMLVideoElement, an HTMLCanvasElement, an ImageBitmap, or an OffscreenCanvas.

sx Optional

The x-axis coordinate of the top left corner of the sub-rectangle of the source image to draw into the destination context. Note that this argument is not included in the 3- or 5-argument syntax.

sy Optional

The y-axis coordinate of the top left corner of the sub-rectangle of the source image to draw into the destination context. Note that this argument is not included in the 3- or 5-argument syntax.

sWidth Optional

The width of the sub-rectangle of the source image to draw into the destination context. If not specified, the entire rectangle from the coordinates specified by sx and sy to the bottom-right corner of the image is used. Note that this argument is not included in the 3- or 5-argument syntax.

sHeight Optional

The height of the sub-rectangle of the source image to draw into the destination context. Note that this argument is not included in the 3- or 5-argument syntax.

dx

The x-axis coordinate in the destination canvas at which to place the top-left corner of the source image. Note that this argument is not included in the 3-argument syntax.

dy

The y-axis coordinate in the destination canvas at which to place the top-left corner of the source image. Note that this argument is not included in the 3-argument syntax.

dWidth

The width to draw the image in the destination canvas. This allows scaling of the drawn image. If not specified, the image is not scaled in width when drawn. Note that this argument is not included in the 3-argument syntax.

dHeight

The height to draw the image in the destination canvas. This allows scaling of the drawn image. If not specified, the image is not scaled in height when drawn. Note that this argument is not included in the 3-argument syntax.

Exceptions thrown

INDEX_SIZE_ERR

If the canvas or source rectangle width or height is zero.

INVALID_STATE_ERR

The image has no image data.

TYPE_MISMATCH_ERR

The specified source element isn't supported.

NS_ERROR_NOT_AVAILABLE

The image is not loaded yet. Use .complete === true and .onload to determine when it is ready.

Examples

Drawing an image to the canvas

This example draws an image to the canvas using the drawImage() method.

HTML

<canvas id="canvas"></canvas>
<div style="display:none;">
  <img id="source"
       src="https://mdn.mozillademos.org/files/5397/rhino.jpg"
       width="300" height="227">
</div>

JavaScript

The source image is taken from the coordinates (33, 71), with a width of 104 and a height of 124. It is drawn to the canvas at (21, 20), where it is given a width of 87 and a height of 104.

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

image.addEventListener('load', e => {
  ctx.drawImage(image, 33, 71, 104, 124, 21, 20, 87, 104);
});

Result

Understanding source element size

The drawImage() method uses the source element's intrinsic size in CSS pixels when drawing.

For example, if you load an Image and specify the optional size parameters in its constructor, you will have to use the naturalWidth and naturalHeight properties of the created instance to properly calculate things like crop and scale regions, rather than element.width and element.height. The same goes for videoWidth and videoHeight if the element is a <video> element, and so on.

HTML

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

JavaScript

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

const image = new Image(60, 45); // Using optional size for image
image.onload = drawImageActualSize; // Draw when image has loaded

// Load an image of intrinsic size 300x227 in CSS pixels
image.src = 'https://mdn.mozillademos.org/files/5397/rhino.jpg';

function drawImageActualSize() {
  // Use the intrinsic size of image in CSS pixels for the canvas element
  canvas.width = this.naturalWidth;
  canvas.height = this.naturalHeight;

  // Will draw the image as 300x227, ignoring the custom size of 60x45
  // given in the constructor
  ctx.drawImage(this, 0, 0);

  // To use the custom size we'll have to specify the scale parameters
  // using the element's width and height properties - lets draw one
  // on top in the corner:
  ctx.drawImage(this, 0, 0, this.width, this.height);
}

Result

Specifications

Browser compatibility

BCD tables only load in the browser

Gecko-specific notes

• Support for flipping the image by using negative values for sw and sh was added in Gecko 5.0 (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2).
• Starting with (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2), drawImage() handles negative arguments in accordance with the specification, by flipping the rectangle around the appropriate axis.
• Specifying a null or undefined image when calling or drawImage() correctly throws a TYPE_MISMATCH_ERR exception starting with (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2).
• Prior to Gecko 7.0 (Firefox 7.0 / Thunderbird 7.0 / SeaMonkey 2.4), Firefox threw an exception if any of the coordinate values was non-finite or zero. As per the specification, this no longer happens.
• Gecko 9.0 (Firefox 9.0 / Thunderbird 9.0 / SeaMonkey 2.6) now correctly supports CORS for drawing images across domains without tainting the canvas.
• Gecko 11.0 (Firefox 11.0 / Thunderbird 11.0 / SeaMonkey 2.8) now allows SVG-as-an-image to be drawn into a canvas without tainting the canvas.

Notes

• drawImage() only works correctly on an HTMLVideoElement when its HTMLMediaElement.readyState is greater than 1 (i.e., seek event fired after setting the currentTime property).
• drawImage() will always use the source element's intrinsic size in CSS pixels when drawing, cropping, and/or scaling.
• In some older browser verisons, drawImage() will ignore all EXIF metadata in images, including the Orientation. This behavior is especially troublesome on iOS devices. You should detect the Orientation yourself and use rotate() to make it right.

See also

• The interface defining this method: CanvasRenderingContext2D