Struct ShapingCache 

pub struct ShapingCache<S: TextShaper> { /* private fields */ }

LRU cache for shaped text runs with generation-based invalidation.

Invalidation policy

The cache tracks a monotonically increasing generation counter. Each cached entry is stamped with the generation at insertion time. When global state changes (font swap, DPR change, zoom), the caller bumps the generation via invalidate. Entries from older generations are treated as misses on access and lazily replaced.

This avoids expensive bulk-clear operations while ensuring correctness.

Thread safety

The cache is not Sync. For multi-threaded use, wrap in a Mutex or use per-thread instances (matching the thread_local_cache feature pattern from WidthCache).

Implementations

impl<S: TextShaper> ShapingCache<S>

pub fn new(shaper: S, capacity: usize) -> Self

Create a new shaping cache with the given backend and capacity.

pub fn shape( &mut self, text: &str, script: Script, direction: RunDirection, font_id: FontId, size_256ths: u32, features: &FontFeatures, ) -> ShapedRun

Shape a text run, returning a cached result if available.

The full shaping key is constructed from the provided parameters. If a cache entry exists with the current generation, it is returned directly. Otherwise, the shaper is invoked and the result is cached.

pub fn shape_with_style( &mut self, text: &str, script: Script, direction: RunDirection, style_id: u64, font_id: FontId, size_256ths: u32, features: &FontFeatures, ) -> ShapedRun

Shape with an explicit style discriminant.

pub fn invalidate(&mut self)

Bump the generation counter, invalidating all cached entries.

Stale entries are not removed eagerly — they are lazily evicted on next access. This makes invalidation O(1).

Call this when:

• The font set changes (font swap, fallback resolution).
• Display DPR changes (affects pixel grid rounding).
• Zoom level changes.

pub fn clear(&mut self)

Clear all cached entries and reset stats.

pub fn stats(&self) -> ShapingCacheStats

Current cache statistics.

pub fn generation(&self) -> u64

Current generation counter.

pub fn shaper(&self) -> &S

Access the underlying shaper.

pub fn resize(&mut self, new_capacity: usize)

Resize the cache capacity.

If the new capacity is smaller than the current size, excess entries are evicted in LRU order.