CropResistantCache class

LRU cache keyed by BlockPerceptualHash. Same shape as PerceptualCache but resilient to crops — ideal for forwarded-image moderation where the same content reappears with different framing.

Trade-off: lookups are O(n × gridSize²) where n is the cache size — roughly 16× slower than PerceptualCache at default settings. Use PerceptualCache when you control framing; reach for CropResistantCache when content arrives from social-sharing pipelines.

final cache = NsfwDetector.instance.cropResistantCache;
final cached = await cache.lookup(bytes);
if (cached != null) return cached;
final result = await NsfwDetector.instance.scanBytes(bytes);
await cache.remember(bytes, result);

Constructors

CropResistantCache({int capacity = 256, int gridSize = BlockPerceptualHash.defaultGridSize, int defaultMinMatchingBlocks = 6, int defaultBlockTolerance = 8})

Properties

capacity → int
Maximum entries retained before LRU eviction.
final
defaultBlockTolerance → int
Default per-block Hamming-distance tolerance.
final
defaultMinMatchingBlocks → int
Default minimum block match count required for lookup to return a hit.
final
gridSize → int
Grid size used when hashing inputs via lookup / remember.
final
hashCode → int
The hash code for this object.
no setterinherited
length → int
Number of entries currently in the cache.
no setter
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

clear() → void
Drops every cached entry.
lookup(Uint8List bytes, {int? minMatchingBlocks, int? blockTolerance}) → Future<ScanResult?>
Looks up bytes. Returns the first stored result whose hash matches at least minMatchingBlocks blocks within blockTolerance bits — promoted to MRU on hit. Returns null on miss or hash failure.
lookupByHash(BlockPerceptualHash hash, {int? minMatchingBlocks, int? blockTolerance}) → ScanResult?
Variant of lookup for callers that already computed the hash.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
remember(Uint8List bytes, ScanResult result) → Future<void>
Stores result keyed by the block-hash of bytes. No-op on hash failure.
rememberByHash(BlockPerceptualHash hash, ScanResult result) → void
Variant of remember for callers that already computed the hash.
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited