Catcrafts/Crafter.Graphics
2
0
Fork 0
Code Issues 1 Pull requests Projects Releases Packages Wiki Activity Actions

perf(ui): LRU-evict the shaped-run cache instead of clearing it (#123)

Browse source 
At kMaxShapedRuns (8192) UIRenderer::ShapeText did a full shapedRuns_.clear().
A stream of unique strings (FPS counters, timers) alongside many stable labels
periodically nuked every stable entry, forcing a full-UI reshape the next frame.

Track recency with an auxiliary std::list<const ShapedRunKey*> (front = most
recently used) holding pointers to the keys owned by the node-based map. A hit
splices its entry to the front; an overflow pops the least-recently-used entry
from the back and erases just that one — both O(1). The hot set of labels,
reshaped every frame, stays at the front and survives, so the churn of unique
strings only recycles the cold tail. Output is byte-identical either way.

InvalidateFont now drops matching entries from both the map and the LRU list.
Adds ShapedRunCacheSize()/IsShapedRunCached() introspection hooks (the policy
isn't observable through output or atlas.dirty) and a ShapeTextCache test that
asserts the cache plateaus at a fixed cap (evict-one, not clear-all), the hot
label survives a churn past the cap, and an untouched cold string is evicted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
catbot 2026-06-18 13:23:34 +00:00
commit 1d7d9f7b8e
3 changed files with 115 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

28
interfaces/Crafter.Graphics-UI.cppm
View file

@ -325,6 +325,17 @@ export namespace Crafter {
// reallocated at the same address would otherwise alias stale runs.
void InvalidateFont(const Font& font) noexcept;
// Shaped-run cache introspection (issue #123). Hits/misses are
// byte-identical and a re-shape of an already-rasterised string leaves
// the atlas clean, so the LRU eviction policy isn't observable through
// output alone — these let tests assert that the cache stays bounded
// and that the hot set survives an overflow. IsShapedRunCached is a
// pure query: it does not bump recency.
std::size_t ShapedRunCacheSize() const noexcept { return shapedRuns_.size(); }
bool IsShapedRunCached(const Font& font, float pxSize,
std::array<float,4> color,
std::string_view utf8) const;
std::uint16_t FontAtlasImageSlot() const noexcept { return fontAtlasImageSlot_; }
std::uint16_t FontAtlasSamplerSlot() const noexcept { return fontAtlasSamplerSlot_; }
@ -362,12 +373,25 @@ export namespace Crafter {
struct ShapedRun {
std::vector<GlyphItem> glyphs; // origin-relative
float advance = 0;
// Position of this run's key in shapedRunsLru_ (front = most
// recently used). Lets a hit splice the entry to the front and an
// overflow pop the least-recently-used entry, both O(1).
std::list<const ShapedRunKey*>::iterator lruIt{};
};
// Soft cap. A pathological caller drawing a fresh string every frame
// would grow this without bound; on overflow we drop everything and
// rebuild (correctness is unaffected, only the hit rate after a flush).
// would grow this without bound; on overflow we evict the single
// least-recently-used run (issue #123) rather than clearing the whole
// cache. The hot set of stable labels — reshaped every frame, so always
// near the front — stays resident, while a churn of unique strings
// (FPS counters, timers) only recycles the cold tail. Correctness is
// unaffected either way; this just avoids the periodic full-UI reshape
// spike the old clear() caused.
static constexpr std::size_t kMaxShapedRuns = 8192;
std::unordered_map<ShapedRunKey, ShapedRun, ShapedRunKeyHash> shapedRuns_;
// LRU recency order for shapedRuns_; front = most recently used. Holds
// pointers to the keys owned by the map — stable across rehash because
// unordered_map is node-based — so eviction never re-hashes the world.
std::list<const ShapedRunKey*> shapedRunsLru_;
ImageSlot outImageSlot_;
ImageSlot fontAtlasImageSlot_;