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Krzysztof kuhy Rudnicki
0798f7b1d0
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
67 lines
2.4 KiB
Dart
67 lines
2.4 KiB
Dart
/// Shrinks a picked or pasted image to what a note needs, before it is stored
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/// or uploaded.
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///
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/// Phone photos are 3–8 MB with GPS coordinates in their EXIF. Every image is
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/// re-encoded here: the recorded rotation is applied to the pixels first (so
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/// dropping EXIF does not leave a portrait photo lying on its side), the long
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/// side is capped at [kMaxImageSide], and the result is a JPEG with no
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/// metadata at all.
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///
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/// Pure Dart (`package:image`), so the Android app and the desktop wrapper
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/// run the same code; the web page never decodes images, it hands the raw
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/// bytes to the wrapper.
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library;
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import 'dart:isolate';
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import 'dart:math' as math;
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import 'dart:typed_data';
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import 'package:image/image.dart' as img;
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/// Longest side, in pixels, of a stored image.
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const kMaxImageSide = 2560;
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/// JPEG quality of a stored image.
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const kJpegQuality = 85;
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/// Re-encodes [bytes] as a metadata-free JPEG no larger than [kMaxImageSide]
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/// on its long side, or returns null when [bytes] is not a decodable image.
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Uint8List? prepareImage(Uint8List bytes) {
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final decoded = _decode(bytes);
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if (decoded == null) return null;
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var image = img.bakeOrientation(decoded);
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final longSide = math.max(image.width, image.height);
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if (longSide > kMaxImageSide) {
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image = image.width >= image.height
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? img.copyResize(image, width: kMaxImageSide)
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: img.copyResize(image, height: kMaxImageSide);
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}
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if (image.hasAlpha) image = _flattenOntoWhite(image);
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image.exif = img.ExifData();
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return img.encodeJpg(image, quality: kJpegQuality);
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}
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/// [prepareImage] off the calling isolate: decoding a 12 MP photo takes long
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/// enough to drop frames if it runs on the UI isolate.
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Future<Uint8List?> prepareImageInBackground(Uint8List bytes) =>
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Isolate.run(() => prepareImage(bytes));
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/// `decodeImage` returns null for most non-images but *throws* (a
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/// RangeError from its PSD sniffer, seen on a 3-byte input) for others; both
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/// mean "not an image" here.
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img.Image? _decode(Uint8List bytes) {
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try {
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return img.decodeImage(bytes);
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} on Object {
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return null;
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}
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}
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/// JPEG has no alpha: without this a transparent screenshot's clear pixels
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/// come out as whatever colour their RGB happened to hold, usually black.
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img.Image _flattenOntoWhite(img.Image image) {
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final background = img.Image(width: image.width, height: image.height)
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..clear(img.ColorRgb8(255, 255, 255));
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return img.compositeImage(background, image);
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}
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