instantiateImageCodecFromBuffer function Null safety
- ImmutableBuffer buffer,
- {int? targetWidth,
- int? targetHeight,
- bool allowUpscaling = true}
Instantiates an image Codec.
This method is a convenience wrapper around the ImageDescriptor API, and
using ImageDescriptor directly is preferred since it allows the caller to
make better determinations about how and whether to use the targetWidth
and targetHeight
parameters.
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 targetWidth
and targetHeight
arguments specify the size of the
output image, in image pixels. If they are not equal to the intrinsic
dimensions of the image, then the image will be scaled after being decoded.
If the allowUpscaling
parameter is not set to true, both dimensions will
be capped at the intrinsic dimensions of the image, even if only one of
them would have exceeded those intrinsic dimensions. If exactly one of these
two arguments is specified, then the aspect ratio will be maintained while
forcing the image to match the other given dimension. If neither is
specified, then the image maintains its intrinsic size.
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. If the image must be scaled
up, the allowUpscaling
parameter must be set to true.
The returned future can complete with an error if the image decoding has failed.
Implementation
Future<Codec> instantiateImageCodecFromBuffer(
ImmutableBuffer buffer, {
int? targetWidth,
int? targetHeight,
bool allowUpscaling = true,
}) async {
final ImageDescriptor descriptor = await ImageDescriptor.encoded(buffer);
if (!allowUpscaling) {
if (targetWidth != null && targetWidth > descriptor.width) {
targetWidth = descriptor.width;
}
if (targetHeight != null && targetHeight > descriptor.height) {
targetHeight = descriptor.height;
}
}
buffer.dispose();
return descriptor.instantiateCodec(
targetWidth: targetWidth,
targetHeight: targetHeight,
);
}