CanvasRenderingContext2D.putImageData() - Web APIs 编辑

The CanvasRenderingContext2D.putImageData() method of the Canvas 2D API paints data from the given ImageData object onto the canvas. If a dirty rectangle is provided, only the pixels from that rectangle are painted. This method is not affected by the canvas transformation matrix.

Note: Image data can be retrieved from a canvas using the getImageData() method.

You can find more information about putImageData() and general manipulation of canvas contents in the article Pixel manipulation with canvas.

Syntax

void ctx.putImageData(imageData, dx, dy);
void ctx.putImageData(imageData, dx, dy, dirtyX, dirtyY, dirtyWidth, dirtyHeight);

Parameters

imageData

An ImageData object containing the array of pixel values.

dx

Horizontal position (x coordinate) at which to place the image data in the destination canvas.

dy

Vertical position (y coordinate) at which to place the image data in the destination canvas.

dirtyX Optional

Horizontal position (x coordinate) of the top-left corner from which the image data will be extracted. Defaults to 0.

dirtyY Optional

Vertical position (y coordinate) of the top-left corner from which the image data will be extracted. Defaults to 0.

dirtyWidth Optional

Width of the rectangle to be painted. Defaults to the width of the image data.

dirtyHeight Optional

Height of the rectangle to be painted. Defaults to the height of the image data.

Errors thrown

NotSupportedError

Thrown if any of the arguments is infinite.

InvalidStateError

Thrown if the ImageData object's data has been detached.

Examples

Understanding putImageData

To understand what this algorithm does under the hood, here is an implementation on top of CanvasRenderingContext2D.fillRect().

HTML

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

JavaScript

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

function putImageData(ctx, imageData, dx, dy,
    dirtyX, dirtyY, dirtyWidth, dirtyHeight) {
  var data = imageData.data;
  var height = imageData.height;
  var width = imageData.width;
  dirtyX = dirtyX || 0;
  dirtyY = dirtyY || 0;
  dirtyWidth = dirtyWidth !== undefined? dirtyWidth: width;
  dirtyHeight = dirtyHeight !== undefined? dirtyHeight: height;
  var limitBottom = dirtyY + dirtyHeight;
  var limitRight = dirtyX + dirtyWidth;
  for (var y = dirtyY; y < limitBottom; y++) {
    for (var x = dirtyX; x < limitRight; x++) {
      var pos = y * width + x;
      ctx.fillStyle = 'rgba(' + data[pos*4+0]
                        + ',' + data[pos*4+1]
                        + ',' + data[pos*4+2]
                        + ',' + (data[pos*4+3]/255) + ')';
      ctx.fillRect(x + dx, y + dy, 1, 1);
    }
  }
}

// Draw content onto the canvas
ctx.fillRect(0, 0, 100, 100);
// Create an ImageData object from it
var imagedata = ctx.getImageData(0, 0, 100, 100);
// use the putImageData function that illustrates how putImageData works
putImageData(ctx, imagedata, 150, 0, 50, 50, 25, 25);

Result

Data loss due to browser optimization

 Due to the lossy nature of converting to and from premultiplied alpha color values, pixels that have just been set using putImageData() might be returned to an equivalent getImageData() as different values.

JavaScript

const canvas = document.createElement("canvas");
canvas.width = 1;
canvas.height = 1;
const context = canvas.getContext("2d");
const imgData = context.getImageData(0, 0, canvas.width, canvas.height);
const pixels = imgData.data;
pixels[0 + 0] = 1;
pixels[0 + 1] = 127;
pixels[0 + 2] = 255;
pixels[0 + 3] = 1;
console.log("before:", pixels);
context.putImageData(imgData, 0, 0);
const imgData2 = context.getImageData(0, 0, canvas.width, canvas.height);
const pixels2 = imgData2.data;
console.log("after:", pixels2);

The output might look like:

before: Uint8ClampedArray(4) [ 1, 127, 255, 1 ]
after: Uint8ClampedArray(4) [ 255, 255, 255, 1 ]

Specifications

Browser compatibility

BCD tables only load in the browser

Gecko-specific notes

• Starting in Gecko 10.0 (Firefox 10.0 / Thunderbird 10.0 / SeaMonkey 2.7), non-finite values to any of these parameters cause the call to putImageData() to be silently ignored, rather than throwing an exception.
• To comply with the specification, starting with Gecko 16.0 (Firefox 16.0 / Thunderbird 16.0 / SeaMonkey 2.13), a call with an invalid number of arguments (only 3 or 7 arguments are valid), will now throw an error (bug 762657).

See also

• The interface defining this method: CanvasRenderingContext2D
• ImageData object
• CanvasRenderingContext2D.getImageData()
• Pixel manipulation with canvas