88 lines
2.5 KiB
Dart
88 lines
2.5 KiB
Dart
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// lib/editor/render/ink_picture_cache.dart
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//
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// Bounded LRU cache of ui.Picture objects keyed by "hostId:revision".
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//
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// Resolution-independent: ink is vector, so a single Picture is valid at any
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// zoom level. There are NO DPI buckets.
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//
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// Evicted Pictures are disposed via a post-frame callback so Flutter's raster
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// thread is never asked to delete a Picture it may still be reading.
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import 'dart:collection';
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import 'dart:ui' as ui;
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import 'package:flutter/widgets.dart';
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/// Bounded LRU cache of [ui.Picture]s keyed by a string (typically
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/// `"$hostId:$revision"`).
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///
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/// Usage:
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/// ```dart
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/// final picture = cache.getOrBuild(hostId, store.revision, size, () {
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/// final recorder = ui.PictureRecorder();
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/// final canvas = ui.Canvas(recorder);
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/// // … draw …
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/// return recorder.endRecording();
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/// });
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/// canvas.drawPicture(picture);
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/// ```
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class InkPictureCache {
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InkPictureCache({int maxSize = 12}) : _maxSize = maxSize;
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final int _maxSize;
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// LinkedHashMap preserves insertion order; we move accessed entries to the
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// back so the front is always the least-recently used.
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final LinkedHashMap<String, ui.Picture> _cache =
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LinkedHashMap<String, ui.Picture>();
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/// Returns a cached [ui.Picture] for [key], or calls [build] to create one.
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///
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/// The [key] should encode all inputs that affect the picture content (host
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/// id + revision, at minimum). [size] and [build] are only used on a cache
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/// miss.
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ui.Picture getOrBuild(
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String hostId,
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int revision,
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ui.Size size,
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ui.Picture Function() build,
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) {
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final key = '$hostId:$revision';
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if (_cache.containsKey(key)) {
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// Promote to most-recently-used by reinserting at the back.
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final pic = _cache.remove(key)!;
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_cache[key] = pic;
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return pic;
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}
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final picture = build();
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_cache[key] = picture;
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// Evict least-recently-used entries beyond the cap.
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while (_cache.length > _maxSize) {
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final lruKey = _cache.keys.first;
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final evicted = _cache.remove(lruKey)!;
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_disposeDeferred(evicted);
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}
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return picture;
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}
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/// Disposes all cached Pictures, deferring the actual disposal to a
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/// post-frame callback so any in-flight raster work can complete.
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void dispose() {
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final pictures = List<ui.Picture>.from(_cache.values);
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_cache.clear();
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for (final pic in pictures) {
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_disposeDeferred(pic);
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}
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}
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static void _disposeDeferred(ui.Picture picture) {
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WidgetsBinding.instance.addPostFrameCallback((_) {
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picture.dispose();
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});
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}
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}
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