Skip to content

Instantly share code, notes, and snippets.

@bambinoua
Forked from dnfield/image_size_data.dart
Created February 23, 2023 15:23
Show Gist options
  • Save bambinoua/ffb51f94d091aa8be5cb6b1941a5f6be to your computer and use it in GitHub Desktop.
Save bambinoua/ffb51f94d091aa8be5cb6b1941a5f6be to your computer and use it in GitHub Desktop.
Image size parsing in Dart
import 'dart:typed_data';
import 'package:meta/meta.dart';
/// Image formats supported by Flutter.
enum ImageFormat {
/// A Portable Network Graphics format image.
png,
/// A JPEG format image.
///
/// This library does not support JPEG 2000.
jpeg,
/// A WebP format image.
webp,
/// A Graphics Interchange Format image.
gif,
/// A Windows Bitmap format image.
bmp,
}
/// Provides details about image format information for raw compressed bytes
/// of an image.
abstract class ImageSizeData {
/// Allows subclasses to be const.
const ImageSizeData({
@required this.format,
@required this.width,
@required this.height,
}) : assert(format != null),
assert(width != null),
assert(width >= 0),
assert(height != null),
assert(height >= 0);
/// Creates an appropriate [ImageSizeData] for the source `bytes`, if possible.
///
/// Only supports image formats supported by Flutter.
factory ImageSizeData.fromBytes(Uint8List bytes) {
if (bytes == null || bytes.isEmpty) {
throw ArgumentError('bytes');
} else if (PngImageSizeData.matches(bytes)) {
return PngImageSizeData._(bytes.buffer.asByteData());
} else if (GifImageSizeData.matches(bytes)) {
return GifImageSizeData._(bytes.buffer.asByteData());
} else if (JpegImageSizeData.matches(bytes)) {
return JpegImageSizeData._fromBytes(bytes.buffer.asByteData());
} else if (WebPImageSizeData.matches(bytes)) {
return WebPImageSizeData._(bytes.buffer.asByteData());
} else if (BmpImageSizeData.matches(bytes)) {
return BmpImageSizeData._(bytes.buffer.asByteData());
} else {
return null;
}
}
/// The [ImageFormat] this instance represents.
final ImageFormat format;
/// The width, in pixels, of the image.
///
/// If the image is multi-frame, this is the width of the first frame.
final int width;
/// The height, in pixels, of the image.
///
/// If the image is multi-frame, this is the height of the first frame.
final int height;
/// The esimated size of the image in bytes.
///
/// The `withMipmapping` parameter controls whether to account for mipmapping
/// when decompressing the image. Flutter will use this when possible, at the
/// cost of slightly more memory usage.
int decodedSizeInBytes({bool withMipmapping = true}) {
if (withMipmapping) {
return (width * height * 4.3).ceil();
}
return width * height * 4;
}
}
/// The [ImageSizeData] for a PNG image.
class PngImageSizeData extends ImageSizeData {
PngImageSizeData._(ByteData data)
: super(
format: ImageFormat.png,
width: data.getUint32(16, Endian.big),
height: data.getUint32(20, Endian.big),
);
/// Returns true if `bytes` starts with the expected header for a PNG image.
static bool matches(Uint8List bytes) {
return bytes != null
&& bytes.lengthInBytes > 20
&& bytes[0] == 0x89
&& bytes[1] == 0x50
&& bytes[2] == 0x4E
&& bytes[3] == 0x47
&& bytes[4] == 0x0D
&& bytes[5] == 0x0A
&& bytes[6] == 0x1A
&& bytes[7] == 0x0A;
}
}
/// The [ImageSizeData] for a GIF image.
class GifImageSizeData extends ImageSizeData {
GifImageSizeData._(ByteData data) : super(
format: ImageFormat.gif,
width: data.getUint16(6, Endian.little),
height: data.getUint16(8, Endian.little),
);
/// Returns true if `bytes` starts with the expected header for a GIF image.
static bool matches(Uint8List bytes) {
return bytes != null
&& bytes.lengthInBytes > 8
&& bytes[0] == 0x47
&& bytes[1] == 0x49
&& bytes[2] == 0x46
&& bytes[3] == 0x38
&& (bytes[4] == 0x37 || bytes[4] == 0x39) // 7 or 9
&& bytes[5] == 0x61;
}
}
/// The [ImageSizeData] for a JPEG image.
///
/// This library does not support JPEG2000 images.
class JpegImageSizeData extends ImageSizeData {
JpegImageSizeData._({int width, int height}) : super(
format: ImageFormat.jpeg,
width: width,
height: height,
);
factory JpegImageSizeData._fromBytes(ByteData data) {
int index = 4; // Skip the first header bytes (already validated).
index += data.getUint16(index, Endian.big);
while (index < data.lengthInBytes) {
if (data.getUint8(index) != 0xFF) {
// Start of block
throw StateError('Invalid JPEG file');
}
if (data.getUint8(index + 1) == 0xC0) {
// Start of frame 0
return JpegImageSizeData._(
height: data.getUint16(index + 5, Endian.big),
width: data.getUint16(index + 7, Endian.big),
);
}
index += 2;
index += data.getUint16(index, Endian.big);
}
return null;
}
/// Returns true if `bytes` starts with the expected header for a JPEG image.
static bool matches(Uint8List bytes) {
return bytes != null
&& bytes.lengthInBytes > 12
&& bytes[0] == 0xFF
&& bytes[1] == 0xD8
&& bytes[2] == 0xFF;
}
}
/// The [ImageSizeData] for a WebP image.
class WebPImageSizeData extends ImageSizeData {
WebPImageSizeData._(ByteData data) : super(
format: ImageFormat.webp,
width: data.getUint16(26, Endian.little),
height: data.getUint16(28, Endian.little),
);
/// Returns true if `bytes` starts with the expected header for a WebP image.
static bool matches(Uint8List bytes) {
return bytes != null
&& bytes.lengthInBytes > 28
&& bytes[0] == 0x52 // R
&& bytes[1] == 0x49 // I
&& bytes[2] == 0x46 // F
&& bytes[3] == 0x46 // F
&& bytes[8] == 0x57 // W
&& bytes[9] == 0x45 // E
&& bytes[10] == 0x42 // B
&& bytes[11] == 0x50; // P
}
}
/// The [ImageSizeData] for a BMP image.
class BmpImageSizeData extends ImageSizeData {
BmpImageSizeData._(ByteData data) : super(
format: ImageFormat.bmp,
width: data.getInt32(18, Endian.little),
height: data.getInt32(22, Endian.little)
);
/// Returns true if `bytes` starts with the expected header for a WebP image.
static bool matches(Uint8List bytes) {
return bytes != null
&& bytes.lengthInBytes > 22
&& bytes[0] == 0x42
&& bytes[1] == 0x4D;
}
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment