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Load each glyph-fallback face once per font system - #558
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A character missing from a run's font loaded every fallback candidate anew, and the only cache lived for a single text run. Each load built a fresh face with a new id, so the canvas glyph cache missed as well. With the Foxit CFF substitutes, whose loading parses every private dictionary and builds a charmap from the whole charset, text-heavy pages that fall back took over ten times longer to interpret, on every redraw. FontSystem now keeps the faces it loads for in-memory fallback programs, keyed by buffer address, length, format and face index, and holds each source so its buffer cannot be freed and its address reused. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Summary
A character missing from a run's font loaded every fallback candidate anew, and the only cache (
FallbackCache) lived for a single text run. Each load built a fresh face with a newFontFaceId, so the canvas glyph outline cache missed too. With the Foxit CFF substitutes, whose loading parses every private dictionary and builds a charmap from the whole charset, pages whose text falls back took over 10× longer to interpret, on every redraw in the Skia viewer.FontSystemnow keeps the faces it loads for in-memory fallback programs, keyed by buffer address, length, format and face index. It holds each source so its buffer cannot be freed and its address reused.Measurements
Page interpretation (
record_ms, conformance worker,regressionprofile) for a text-heavy document whose embedded TrueType subsets fall back:Bisecting merges showed 7–9 ms up to #555, rising to ~125 ms at #556. Rendered output is byte-identical before and after.
Test plan
cargo fmt --check,cargo clippy --all --workspacecargo test -p pdf-text-engine -p pdf-font -p pdf-canvas -p pdf-renderer🤖 Generated with Claude Code