instantiateImageCodec method

Future<Codec> instantiateImageCodec(Uint8List bytes, { int? cacheWidth, int? cacheHeight, bool allowUpscaling = false, })

Implementation

Future<Codec> instantiateImageCodec(
  Uint8List bytes, {
  int? cacheWidth,
  int? cacheHeight,
  bool allowUpscaling = false,
}) async {
  assert(cacheWidth == null || cacheWidth > 0);
  assert(cacheHeight == null || cacheHeight > 0);

  final ImmutableBuffer buffer = await ImmutableBuffer.fromUint8List(bytes);
  final ImageDescriptor descriptor = await ImageDescriptor.encoded(buffer);

  double naturalWidth = descriptor.width.toDouble();
  double naturalHeight = descriptor.height.toDouble();

  int? targetWidth;
  int? targetHeight;

  // Image will be resized according to its aspect radio if object-fit is not fill.
  // https://www.w3.org/TR/css-images-3/#propdef-object-fit
  if (cacheWidth != null && cacheHeight != null) {
    // When targetWidth or targetHeight is not set at the same time,
    // image will be resized according to its aspect radio.
    // https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/painting/box_fit.dart#L152
    if (objectFit == BoxFit.contain) {
      if (cacheWidth / cacheHeight > naturalWidth / naturalHeight) {
        targetHeight = cacheHeight;
      } else {
        targetWidth = cacheWidth;
      }

    // Resized image should maintain its intrinsic aspect radio event if object-fit is fill
    // which behaves just like object-fit cover otherwise the cached resized image with
    // distorted aspect ratio will not work when object-fit changes to not fill.
    } else if (objectFit == BoxFit.fill || objectFit == BoxFit.cover) {
      if (cacheWidth / cacheHeight > naturalWidth / naturalHeight) {
        targetWidth = cacheWidth;
      } else {
        targetHeight = cacheHeight;
      }

    // Image should maintain its aspect radio and not resized if object-fit is none.
    } else if (objectFit == BoxFit.none) {
      targetWidth = descriptor.width;
      targetHeight = descriptor.height;

    // If image size is smaller than its natural size when object-fit is contain,
    // scale-down is parsed as none, otherwise parsed as contain.
    } else if (objectFit == BoxFit.scaleDown) {
      if (cacheWidth / cacheHeight > naturalWidth / naturalHeight) {
        if (cacheHeight > descriptor.height * window.devicePixelRatio) {
          targetWidth = descriptor.width;
          targetHeight = descriptor.height;
        } else {
          targetHeight = cacheHeight;
        }
      } else {
        if (cacheWidth > descriptor.width * window.devicePixelRatio) {
          targetWidth = descriptor.width;
          targetHeight = descriptor.height;
        } else {
          targetWidth = cacheWidth;
        }
      }
    }
  } else {
    targetWidth = cacheWidth;
    targetHeight = cacheHeight;
  }

  // Resize image size should not be larger than its natural size.
  if (!allowUpscaling) {
    if (targetWidth != null && targetWidth > descriptor.width * window.devicePixelRatio) {
      targetWidth = descriptor.width;
    }
    if (targetHeight != null && targetHeight > descriptor.height * window.devicePixelRatio) {
      targetHeight = descriptor.height;
    }
  }

  return descriptor.instantiateCodec(
    targetWidth: targetWidth,
    targetHeight: targetHeight,
  );
}