89 lines
3.1 KiB
Dart
89 lines
3.1 KiB
Dart
/*
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* Copyright (c) 2024-2026 Fabian Freund.
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*
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* This file is part of WebLibre
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* (see https://weblibre.eu).
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as
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* published by the Free Software Foundation, either version 3 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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import 'dart:ui';
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/// What makes one decoded image the *same* image as another.
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///
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/// Deliberately a record rather than a single combined `int`: [digest] is a
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/// 64-bit content hash, and folding it together with the decode options via
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/// `Object.hash` would truncate the whole thing to 30 bits (Dart caps hash
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/// codes at `0x3fffffff`) and leave the result standing in as the identity
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/// with no exact comparison behind it. As a record, hash codes only pick the
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/// bucket and structural `==` decides equality, so the full digest and the
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/// exact options both count.
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typedef ImageIdentity = ({
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int digest,
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int? targetWidth,
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int? targetHeight,
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bool allowUpscaling,
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});
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/// A wrapper around [Image] that compares by a precomputed [ImageIdentity].
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///
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/// Instances are deduped via the decoder's LRU, so the same `EquatableImage`
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/// may be shared across many holders (multiple tabs of the same site, the icon
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/// cache, widget closures). To make that safe, the underlying `ui.Image` is
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/// disposed via a [Finalizer] when this wrapper becomes unreachable — never on
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/// cache eviction or state transitions, where another holder might still be
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/// using it.
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class EquatableImage {
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static final Finalizer<Image> _finalizer = Finalizer<Image>(
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(image) => image.dispose(),
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);
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Image? _value;
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final ImageIdentity _identity;
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bool _isDisposed = false;
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EquatableImage(Image value, {required ImageIdentity identity})
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: _value = value,
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_identity = identity {
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_finalizer.attach(this, value, detach: this);
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}
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/// The underlying ui.Image. Returns null if explicitly disposed.
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Image? get value => _isDisposed ? null : _value;
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/// Whether this image has been explicitly disposed.
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bool get isDisposed => _isDisposed;
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/// Explicitly release the underlying GPU resource now.
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///
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/// Optional — if not called, the resource is freed when this wrapper is
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/// garbage collected. Only call this when you are certain no other holder
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/// still references the image; otherwise prefer to drop your reference
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/// and let GC handle it.
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void dispose() {
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if (_isDisposed) return;
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_isDisposed = true;
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_finalizer.detach(this);
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_value?.dispose();
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_value = null;
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}
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@override
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int get hashCode => _identity.hashCode;
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@override
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bool operator ==(Object other) {
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return other is EquatableImage && other._identity == _identity;
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}
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}
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