instantiateImageCodecWithSize function

Future<Codec> instantiateImageCodecWithSize(
  1. ImmutableBuffer buffer,
  2. {TargetImageSizeCallback? getTargetSize}

Instantiates an image Codec.

This method is a convenience wrapper around the ImageDescriptor API.

The buffer parameter is the binary image data (e.g a PNG or GIF binary data). The data can be for either static or animated images. The following image formats are supported: JPEG, PNG, GIF, Animated GIF, WebP, Animated WebP, BMP, and WBMP. Additional formats may be supported by the underlying platform. Flutter will attempt to call platform API to decode unrecognized formats, and if the platform API supports decoding the image Flutter will be able to render it.

The buffer will be disposed by this method once the codec has been created, so the caller must relinquish ownership of the buffer when they call this method.

The getTargetSize parameter, when specified, will be invoked and passed the image's intrinsic size to determine the size to decode the image to. The width and the height of the size it returns must be positive values greater than or equal to 1, or null. It is valid to return a TargetImageSize that specifies only one of width and height with the other remaining null, in which case the omitted dimension will be scaled to maintain the aspect ratio of the original dimensions. When both are null or omitted, the image will be decoded at its native resolution (as will be the case if the getTargetSize parameter is omitted).

Scaling the image to larger than its intrinsic size should usually be avoided, since it causes the image to use more memory than necessary. Instead, prefer scaling the Canvas transform.

The returned future can complete with an error if the image decoding has failed.

Compatibility note on the web

When running Flutter on the web, only the CanvasKit renderer supports image resizing capabilities (not the HTML renderer). So if image resizing is critical to your use case, and you're deploying to the web, you should build using the CanvasKit renderer.


Future<Codec> instantiateImageCodecWithSize(
  ImmutableBuffer buffer, {
  TargetImageSizeCallback? getTargetSize,
}) async {
  getTargetSize ??= _getDefaultImageSize;
  final ImageDescriptor descriptor = await ImageDescriptor.encoded(buffer);
  try {
    final TargetImageSize targetSize = getTargetSize(descriptor.width, descriptor.height);
    assert(targetSize.width == null || targetSize.width! > 0);
    assert(targetSize.height == null || targetSize.height! > 0);
    return descriptor.instantiateCodec(
      targetWidth: targetSize.width,
      targetHeight: targetSize.height,
  } finally {