Density (pure hi-DPI) was already scale-free: all bookkeeping is in
density-dp and the scale enters only at the px<->dp boundary. But Android
also has a second axis, the user font-size setting (PxPerSp = fontScale *
PxPerDp), and the shaper draws baselines in sp. At a non-default font
scale the rendered line pitch is 16.8*fontScale dp while every logic-side
consumer used the raw 16.8 dp: taps would misplace by up to (fontScale-1)
viewportfuls of lines and scroll clamping would stop short of the bottom.
- ScaleEvent.FontScale + Frame.FontScale closed loop (main reads
gtx.Metric, logic tracks it in State.fontScale).
- EffectiveLineHeight()/EffectiveLineHeightAt(): the font-scale-applied
line height, now used by every consumer (window start, sub-line
remainder, tap mapping, scroll clamp, page size, cursor vertical move,
menu position, chunk-prefetch fallbacks).
- Renderer: GlyphLayout.LineHeight, caret, selection handles, and
highlight all use the scaled ascent/line-height from gtx.Metric.
- font_scale_test.go: 2000-pair tap property test at fontScale 1.3 with
the glyph layout fabricated at the scaled pitch (independent ground
truth), plus EffectiveLineHeight unit test.
- On-device: tap markers landed on exactly the tapped line at font_scale
1.3 (fsline060/080/081) and 0.8 (fsline039); rendered pitch measured
57/35/44 px at 1.3/0.8/1.0 (matches 16.8*fs*2.625); settled-position
window start k = floor(s/lh_eff) verified against the visible top line.
- Docs: architecture.md 6.2 font-scale axis, README two-scale note +
profiler 2s flush staleness note, development plan v10 Phase 11.
Greg Pomerantz
b24aa26446