gputext

GPUText vector text renderer ported to Flutter GPU. The library package lives in packages/gputext/; this repo is a Melos workspace. GPURichText is a near drop-in replacement for RichText whose glyphs are rasterized by an analytic coverage shader (see lib/src/widgets/rich_text.dart for the API surface and current limits).

Demos

The demo app lives in example/ (it depends on the package via path: ../packages/gputext). Run it from there:

cd example
flutter run -d macos
GPUTEXT_DEMO=<page> flutter run -d macos # open a page directly

<page> is one of widgets, pretext, dragon, justify, vars, or bench. dragon is the pretext-playground port: an interactive ASCII dragon whose every glyph is GPU-rendered by the coverage shader — Latin (Lato), CJK (a subset Noto Sans SC), and color emoji (Twemoji, drawn natively as COLR-layer coverage instances) — with per-character home positions laid out by the inner pretext prebuilt (prepare-once / relayout-per-width, shown live in the HUD).

Workspace

From the repo root:

dart pub global activate melos # once
dart pub get # install melos locally
melos bootstrap # link packages and run hooks
melos run build # compile shader bundles (required before analyze)
melos run analyze
melos run test
melos run format # or melos run format:check

Benchmarks

A full-matrix RichText vs GPURichText benchmark lives in example/lib/bench/ and runs as an in-app mode. Run the scripts from example/:

tool/run_bench.sh # full run, compares to baseline
GPUTEXT_BENCH_QUICK=1 tool/run_bench.sh # short smoke run
GPUTEXT_BENCH_FILTER=frame.zoom,cpu. tool/run_bench.sh # subset by id prefix
tool/run_bench.sh --update-baseline # promote this run to the baseline

The runner launches the app in profile mode on macOS (keep its window foregrounded — background throttling corrupts frame timings), collects the report from stdout (GPUBENCH: marker lines; the sandboxed app cannot write into the repo), stores it under benchmark/results/, and prints a delta table against benchmark/baseline/macos.json via tool/compare_bench.dart.

Four tiers, methodology mirroring /pretext/pages/benchmark.ts (warmup + median-of-runs, width cycling, DCE sinks; corpus files are copies of /pretext/corpora):

• cpu.* — pure layout: flatten/prepare/relayout vs TextPainter, long-form corpora, Knuth–Plass vs greedy.
• frame.* — end-to-end FrameTiming (build/raster percentiles, jank counts) across cold init, atlas warm-up, idle floor, per-frame repaint / text change / reflow, long-document scroll, transform + InteractiveViewer zoom, widget grids, justification, variable-font animation, the hybrid emoji/CJK and WidgetSpan-heavy paths, and frame.rich_interleave (mixed WidgetSpan kinds/alignments + styled/hybrid runs under reflow).
• mem.* — RSS plus gputext-internal accounting (atlas bytes, cached glyph images, instance buffers, prepare-cache size).
• vis.* — RepaintBoundary captures of paired renderings diffed in Dart (luma MAE/RMSE, size parity, ink coverage), including a 4× zoom crispness case and vis.rich_interleave for the complex WidgetSpan tree.

Reading the numbers: every entry carries a path tag — pure rows isolate gputext; hybrid/cache-disabled rows exercise the native-delegation and WidgetSpan paths and are not comparable with pure rows. GPUText's steady-state paint is a cached-image blit, so static scenarios structurally favor it; weigh them against the dynamic ones (repaint_color, text_update, reflow_width, zooms). Sanity checks (cache-hit expectations, idle floor, zoom re-render counts) are embedded in meta.sanity and fail the report's status when violated.

Hybrid rendering

GPURichText is not a single paint path:

• GPU blit — glyphs covered by a registered GPUFont (including in-engine fontFamilyFallback) are rasterized by the coverage shader into a cached ui.Image, then blitted.
• Platform Text — color-emoji clusters (expandEmojiSpans) and characters no registered font covers (expandUncoveredSpans, often CJK) become baseline-aligned WidgetSpans whose child is stock Flutter Text.
• WidgetSpan children — measured in layout and painted on top of the text image, same as RichText.

Benchmark rows tagged pure isolate the GPU path; hybrid / cache-disabled rows exercise platform delegation and are not comparable. Coverage styling knobs on GPURichText / FrameUniforms: coverageGamma, coverageSharp (default 1, 1 = exact), and minificationGuardPx (default 3.7; raise toward 8 for thumbnail-heavy UIs).

Limits: Impeller / flutter_gpu only (widgets paint blank otherwise); no bidi/RTL shaping; locale is accepted but unused; foreground Paint is flat color only.

API (migrated from windfoil_flutter)

windfoil_flutter	gputext
WindfoilRichText	GPURichText
WindfoilText	GPULabel
Windfoil	GPUText
WindfoilFont	GPUFont
package:windfoil_flutter	package:gputext