feat(p0.5): DPI-bucketed PageTileCache + dpiBucketFor (step 10, automatable slice)
The "heavy" page-bitmap cache (R11/MF2), deliberately SEPARATE from the resolution-independent ink Picture cache: page tiles are only crisp at the DPI they were rasterized for, so TileKey carries a DPI bucket. get()/put() (tiles render async via pdfrx), bounded LRU with MRU promotion, per-key replacement disposes the old image, evictHostsExcept() for scroll-out, and post-frame ui.Image disposal so the raster thread never frees an in-use image. dpiBucketFor() snaps a continuous pinch scale to a coarse bucket (ceil by step, capped at maxBucket) so a smooth zoom re-uses tiles instead of spawning one per frame and bounds retained-DPI memory (~3× cap). The pdfrx tile RENDERING (page_tile.dart) + zoom-settle DPI refresh remain device-gated (crisp-at-4× on the Surface) — only the cache data structure is automatable, and it is here, fully unit-tested. flutter analyze lib/editor clean; 102/102 tests (+12: bucket math, LRU, MRU, host eviction, post-frame disposal via debugDisposed). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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137
lib/editor/pdf/page_tile_cache.dart
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137
lib/editor/pdf/page_tile_cache.dart
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// lib/editor/pdf/page_tile_cache.dart
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//
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// Bounded LRU cache of rasterized PAGE tiles (ui.Image), DPI-bucketed.
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//
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// This is the "heavy" cache (a single A4 page at 3× DPI is ~18 MB) and is
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// DELIBERATELY SEPARATE from the resolution-independent ink Picture cache
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// (render/ink_picture_cache.dart): ink is vector and valid at any zoom, but a
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// page bitmap is only crisp at the DPI it was rasterized for, so its key
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// carries a DPI bucket (R11 / MF2). On zoom-settle the page_tile renderer
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// re-rasterizes at the new bucket and put()s it here; matrix-upscale of a lower
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// bucket is the accepted transient until the new tile lands.
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//
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// Tiles are rendered ASYNCHRONOUSLY (pdfrx PdfPage.render / a re-laid-out
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// PdfPageView), so the cache is get()/put() — NOT getOrBuild — and the caller
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// owns the async render. Evicted images are disposed via a post-frame callback
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// so Flutter's raster thread is never asked to free a ui.Image it may still be
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// sampling this frame.
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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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/// Identity of a cached page tile: which host (page) and which DPI bucket.
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///
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/// The DPI bucket (an integer, e.g. round(scale × base-DPI) snapped to a step)
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/// keeps the key space small so a smooth pinch doesn't spawn a distinct tile
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/// per frame — only per bucket.
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@immutable
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class TileKey {
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const TileKey(this.hostId, this.dpiBucket);
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final String hostId;
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final int dpiBucket;
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@override
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bool operator ==(Object other) =>
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other is TileKey &&
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other.hostId == hostId &&
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other.dpiBucket == dpiBucket;
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@override
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int get hashCode => Object.hash(hostId, dpiBucket);
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@override
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String toString() => 'TileKey($hostId @dpi$dpiBucket)';
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}
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/// Bounded LRU cache of page-tile [ui.Image]s keyed by [TileKey].
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///
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/// Capacity is a TILE COUNT (not bytes); size the window to the device memory
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/// budget — full-DPI tiles for visible ±1 pages, off-window pages downgraded to
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/// a 1× tier elsewhere (see the plan's R10 resolution). Eviction disposes the
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/// image post-frame.
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class PageTileCache {
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PageTileCache({int maxTiles = 6})
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: assert(maxTiles > 0),
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_maxTiles = maxTiles;
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final int _maxTiles;
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// Insertion-ordered; accessed entries are moved to the back so the front is
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// always the least-recently-used.
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final LinkedHashMap<TileKey, ui.Image> _cache =
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LinkedHashMap<TileKey, ui.Image>();
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/// Number of tiles currently retained.
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int get length => _cache.length;
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/// The keys currently retained, most-recently-used LAST.
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Iterable<TileKey> get keys => _cache.keys;
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/// Returns the cached image for [key] (promoting it to most-recently-used),
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/// or null on a miss. The caller renders + [put]s on a miss.
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ui.Image? get(TileKey key) {
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final image = _cache.remove(key);
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if (image == null) return null;
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_cache[key] = image; // promote to MRU
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return image;
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}
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/// Inserts [image] for [key], evicting the least-recently-used tiles beyond
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/// the cap. If a DIFFERENT image was already stored for [key], the old one is
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/// disposed (post-frame). Re-putting the identical image is a no-op promote.
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void put(TileKey key, ui.Image image) {
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final existing = _cache.remove(key);
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if (existing != null && !identical(existing, image)) {
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_disposeDeferred(existing);
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}
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_cache[key] = image;
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while (_cache.length > _maxTiles) {
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final lruKey = _cache.keys.first;
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_disposeDeferred(_cache.remove(lruKey)!);
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}
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}
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/// Evicts every tile whose host is NOT in [liveHostIds] (e.g. pages that
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/// scrolled out of the mounted window). Disposed post-frame.
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void evictHostsExcept(Set<String> liveHostIds) {
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final doomed = _cache.keys
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.where((k) => !liveHostIds.contains(k.hostId))
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.toList(growable: false);
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for (final key in doomed) {
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_disposeDeferred(_cache.remove(key)!);
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}
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}
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/// Disposes all retained tiles (post-frame). Call from the owner's dispose.
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void dispose() {
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final images = List<ui.Image>.from(_cache.values);
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_cache.clear();
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for (final image in images) {
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_disposeDeferred(image);
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}
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}
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static void _disposeDeferred(ui.Image image) {
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// Defer to after the current frame so the raster thread is done with it.
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// If no binding/frame is scheduled (e.g. a unit test that never pumps),
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// fall back to disposing on the next microtask so images aren't leaked.
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final binding = WidgetsBinding.instance;
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binding.addPostFrameCallback((_) => image.dispose());
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binding.scheduleFrame();
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}
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}
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/// Snaps a continuous render scale to a coarse DPI bucket so a smooth pinch
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/// re-uses tiles instead of spawning one per frame. [step] is the bucket
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/// granularity in the same units as [scale] (e.g. 0.5). The result is capped at
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/// [maxBucket] to bound retained-tile memory (the plan's ~3× cap, R11).
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int dpiBucketFor(double scale, {double step = 0.5, int maxBucket = 6}) {
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if (!scale.isFinite || scale <= 0) return 1;
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final bucket = (scale / step).ceil();
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if (bucket < 1) return 1;
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return bucket > maxBucket ? maxBucket : bucket;
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}
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150
test/page_tile_cache_test.dart
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150
test/page_tile_cache_test.dart
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// Unit tests for the DPI-bucketed page-tile cache (P0.5 step 10, automatable
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// slice). Covers LRU eviction, MRU promotion, per-key replacement, host
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// eviction, dpiBucketFor snapping, and post-frame disposal of evicted images.
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//
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// The pdfrx tile RENDERING (page_tile.dart) is device-gated and not tested
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// here; this is the pure cache data structure.
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import 'dart:ui' as ui;
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import 'package:flutter/widgets.dart';
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import 'package:flutter_test/flutter_test.dart';
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import 'package:badnote/editor/pdf/page_tile_cache.dart';
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Future<ui.Image> _img() async {
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final recorder = ui.PictureRecorder();
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Canvas(recorder).drawRect(
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const Rect.fromLTWH(0, 0, 2, 2),
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Paint()..color = const Color(0xFF000000),
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);
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final picture = recorder.endRecording();
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final image = await picture.toImage(2, 2);
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picture.dispose();
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return image;
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}
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void main() {
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TestWidgetsFlutterBinding.ensureInitialized();
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group('dpiBucketFor', () {
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test('snaps continuous scale to a coarse bucket (ceil by step)', () {
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expect(dpiBucketFor(1.0, step: 0.5), 2); // 1.0/0.5 = 2
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expect(dpiBucketFor(1.1, step: 0.5), 3); // ceil(2.2)
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expect(dpiBucketFor(0.4, step: 0.5), 1); // ceil(0.8) = 1
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});
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test('is monotonic non-decreasing in scale', () {
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var prev = 0;
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for (final s in [0.3, 0.6, 1.0, 1.6, 2.0, 2.9]) {
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final b = dpiBucketFor(s, step: 0.5, maxBucket: 100);
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expect(b, greaterThanOrEqualTo(prev));
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prev = b;
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}
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});
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test('caps at maxBucket (bounds retained-DPI memory)', () {
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expect(dpiBucketFor(99.0, step: 0.5, maxBucket: 6), 6);
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});
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test('guards invalid scale', () {
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expect(dpiBucketFor(0), 1);
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expect(dpiBucketFor(-3), 1);
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expect(dpiBucketFor(double.nan), 1);
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});
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});
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group('PageTileCache LRU', () {
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test('get returns null on miss, the image on hit', () async {
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final cache = PageTileCache(maxTiles: 4);
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const key = TileKey('p0', 2);
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expect(cache.get(key), isNull);
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final img = await _img();
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cache.put(key, img);
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expect(identical(cache.get(key), img), isTrue);
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cache.dispose();
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});
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test('TileKey equality is by (hostId, dpiBucket)', () {
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expect(const TileKey('p0', 2), const TileKey('p0', 2));
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expect(const TileKey('p0', 2), isNot(const TileKey('p0', 3)));
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expect(const TileKey('p0', 2), isNot(const TileKey('p1', 2)));
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expect(const TileKey('p0', 2).hashCode, const TileKey('p0', 2).hashCode);
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});
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test('evicts the least-recently-used beyond the cap', () async {
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final cache = PageTileCache(maxTiles: 2);
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cache.put(const TileKey('a', 1), await _img());
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cache.put(const TileKey('b', 1), await _img());
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cache.put(const TileKey('c', 1), await _img()); // evicts 'a'
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expect(cache.length, 2);
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expect(cache.keys, isNot(contains(const TileKey('a', 1))));
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expect(cache.get(const TileKey('a', 1)), isNull);
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expect(cache.get(const TileKey('b', 1)), isNotNull);
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cache.dispose();
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});
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test('get promotes MRU so the OTHER entry is evicted next', () async {
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final cache = PageTileCache(maxTiles: 2);
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cache.put(const TileKey('a', 1), await _img());
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cache.put(const TileKey('b', 1), await _img());
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cache.get(const TileKey('a', 1)); // 'a' now MRU → 'b' is LRU
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cache.put(const TileKey('c', 1), await _img()); // evicts 'b'
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expect(cache.get(const TileKey('a', 1)), isNotNull);
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expect(cache.get(const TileKey('b', 1)), isNull);
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cache.dispose();
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});
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test('evictHostsExcept drops other hosts, keeps live ones', () async {
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final cache = PageTileCache(maxTiles: 8);
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cache.put(const TileKey('p0', 1), await _img());
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cache.put(const TileKey('p0', 2), await _img());
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cache.put(const TileKey('p1', 1), await _img());
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cache.put(const TileKey('p2', 1), await _img());
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cache.evictHostsExcept({'p0', 'p1'});
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expect(cache.keys.map((k) => k.hostId).toSet(), {'p0', 'p1'});
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expect(cache.length, 3);
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cache.dispose();
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});
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});
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group('PageTileCache disposal (post-frame)', () {
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testWidgets('an evicted tile is disposed after the frame', (tester) async {
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final cache = PageTileCache(maxTiles: 1);
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final first = await _img();
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cache.put(const TileKey('a', 1), first);
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cache.put(const TileKey('b', 1), await _img()); // evicts 'a' → defers
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expect(first.debugDisposed, isFalse, reason: 'deferred, not yet');
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await tester.pump(); // run the post-frame callback
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expect(first.debugDisposed, isTrue);
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cache.dispose();
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await tester.pump();
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});
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testWidgets('re-putting a different image for a key disposes the old one',
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(tester) async {
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final cache = PageTileCache(maxTiles: 4);
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final old = await _img();
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cache.put(const TileKey('a', 1), old);
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cache.put(const TileKey('a', 1), await _img());
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await tester.pump();
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expect(old.debugDisposed, isTrue);
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expect(cache.length, 1);
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cache.dispose();
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await tester.pump();
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});
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testWidgets('dispose() frees all retained tiles', (tester) async {
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final cache = PageTileCache(maxTiles: 8);
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final a = await _img();
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final b = await _img();
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cache.put(const TileKey('a', 1), a);
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cache.put(const TileKey('b', 1), b);
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cache.dispose();
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await tester.pump();
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expect(a.debugDisposed, isTrue);
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expect(b.debugDisposed, isTrue);
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expect(cache.length, 0);
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});
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});
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}
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