Greg Pomerantz
b24aa26446
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.
215 lines
11 KiB
Markdown
215 lines
11 KiB
Markdown
# Pad documentation
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Three documents, kept at the level of *what, why, and invariants* — not
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line-by-line code — so they stay true as the implementation evolves.
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| Doc | What it is |
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|---|---|
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| [`spec.md`](./spec.md) | What the app **actually does**, measured performance, the code layout, and an explicit list of deferred features. |
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| [`architecture.md`](./architecture.md) | How it works: single-owner concurrency model, channel topology, Frame handoff contract, ownership rules, editor/browser/render internals. |
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| [`development_plan.md`](./development_plan.md) | The active plan: completed phases, remaining work, and the on-device observation loop. |
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## Package inventory
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| Package | Role |
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|---------|------|
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| `internal/editor` | Chunked buffer, line index, virtualized viewport, IME ops, autosave, logic goroutine, state, Frame |
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| `internal/browser` | Directory browsing, search, sort, pagination, browser state machine |
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| `internal/ui` | Element tree, frame layout, renderer (op-based), IME wiring, gestures |
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| `internal/perf` | Default-off performance profiler (per-logic-frame cadence + scroll state → CSV) |
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| `internal/io/pool` | Worker pool (8 workers, 2 priority lanes) + file/dir tasks |
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| `internal/test/e2e` | Harness driving the real `Logic` + `Inspect` |
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| `cmd/pad` | `main.go` (entry), `impl_android.go` (base path) |
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## Documentation policy
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1. **Docs describe invariants and contracts, not code lines.** If a document
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has to change on every refactor, it is too detailed — delete it or raise
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its level of abstraction. Point-in-time implementation plans are deleted
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once implemented (the previous `*_implementation_plan.md`,
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`touch.md`, `element_model.md`, `layout_rendering.md`,
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`virtual_scroll_render_optimization.md`, and `conflict_resolution.md` were
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removed in the 2026-08 doc reorganization for this reason).
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2. **Unbuilt behavior is not spec'd.** Requirements that are not in the code
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live in `spec.md` §7 (deferred), never as if they worked.
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3. **Code wins.** When doc and code disagree, fix the doc.
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## Build & install (Android, this workstation)
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Prereqs on this box (already installed): JDK 17, Go, Android SDK at
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`~/android-sdk` (platform-tools, build-tools 35.0.0, emulator, NDK),
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`gogio@v0.10.0` in `~/go/bin`, debug keystore at
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`~/.android/debug.keystore`. Env vars are set in `~/.bashrc`.
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**Build + install with `./scripts/build_emu.sh`** (add `--no-install` to
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build only). It is self-contained: checks the prereqs, auto-downloads
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apktool v3.0.3 to `~/android-sdk/tools/apktool.jar` if missing, and uses a
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temporary work dir. Output: `cmd/pad/pad-emu.apk`.
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What it does, and why (gogio cannot inject manifest permissions):
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1. `gogio -target android -targetsdk 35 -arch amd64` → raw APK (from `cmd/pad/`)
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2. `apktool d` → decode
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3. Inject `<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE"/>`
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(without it, Android 11+ blocks listing `/storage/emulated/0`)
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4. `apktool b` → rebuild
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5. `apksigner sign` with the debug key → `cmd/pad/pad-emu.apk`
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6. `adb install -r` (skipped with `--no-install`)
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## Emulator + on-device debug: `scripts/emu.sh`
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All emulator lifecycle and on-device debug operations go through
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`scripts/emu.sh` (headless AVD `pad_avd`, API 35): `up` / `down` /
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`status`, `app start|stop|restart`, `shot`, `log`, `tap X Y`, `type TEXT`,
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`cmd <top|bottom|frac F|dp N>` (one-shot editor debug command),
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`perf on|off|pull` (in-app profiler), `push`/`pull` (Notes files). See the
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script header for the full list and the device paths it encodes.
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Snapshot behavior: the AVD auto-saves an instant-boot snapshot on clean
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`down` (restore ~10 s vs ~20 s cold boot). A corrupted snapshot makes the
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emulator segfault during restore; `up` detects that and falls back to a
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cold boot, and the next `down` re-saves a good snapshot (self-healing).
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Always stop with `down` — SIGKILLing the emulator corrupts the snapshot.
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App package/activity: `pad.pad / org.gioui.GioActivity`. Default root
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directory: `/storage/emulated/0/Notes`.
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## Screen coordinates
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The app has several coordinate spaces (screen/display/app-local px, app dp,
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text-local, window-relative glyph bytes, absolute file bytes); mixing them
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up is the #1 cause of tap-test and cursor bugs. (Measured 2026-08-16 on
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`pad_avd`; the 128 px offset and the 2.625 scale are device-config facts —
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re-derive with `adb shell wm size`, `adb shell wm density`, `dumpsys
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window`, and a fresh screenshot with the keyboard open if the device config
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ever changes.)
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| space | size | used by |
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|--------------|-----------|------------------------------------------|
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| screen px | 1080×2400 | `adb input tap`, `screencap` output |
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| display px | 900×2000 | what you see when reading a PNG (vision) |
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| app-local px | 1080×2272 | what Gio receives (`evtPos`) |
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| pt | — | app layout units |
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Conversions:
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- display → screen: **× 1.2** (both axes)
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- screen → app-local: **Y − 128** (surface starts below the status bar; X unchanged)
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- app-local px → pt: **÷ 2.625** (density 420)
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There are TWO independent scale factors, not one:
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- **Density** (`PxPerDp`, 2.625 here): the px↔dp conversion above. All
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geometry bookkeeping is in density-dp, so the pipeline is scale-free and
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holds at any display density (verified algebraically; the tap/scroll proof
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in Phase 10 uses no device numbers).
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- **User font scale** (`PxPerSp/PxPerDp`, e.g. `settings put system
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font_scale 1.3`): scales the *text* only (the shaper draws in sp), so the
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rendered line pitch is `16.8 × fontScale` dp. The logic side tracks this
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via `EffectiveLineHeight()` and every line-height consumer uses it
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(window start, sub-line remainder, tap mapping, scroll clamp, caret,
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handles, highlight). Change it and the line pitch on screen changes
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(57 px/line at 1.3× vs 44 px/line at 1.0× on this AVD).
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On-device verification notes:
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- The profiler CSV (`/storage/emulated/0/PadPerf/logic_frames.csv`) flushes
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to disk at most every 2 s, so `tail` can be up to 2 s stale — a scroll
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fling still settling reads as "settled" if two reads fall in the same
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flush window. Compare rows ≥ 2.5 s apart, taken after the last input.
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- The tap test is the ground truth and does not depend on the profiler:
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screenshot → visually identify a line → tap it → type a marker → read the
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file off the device → the marker must be on exactly the tapped line.
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Full pipeline, screen → file byte (each hop has exactly one place it
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happens; the app is internally consistent, so errors only appear at the
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hops, not inside a space):
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1. **screen px → window px → app dp** — OS/Gio. Taps you inject land here;
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this is the only space `adb`/screenshots touch.
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2. **app dp → text-local dp** — the tap/drag handlers
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(`localX = x − EditorRegion.X`, `localY = tapLocalY(...)`).
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**Y adds only the sub-line scroll remainder**, never the full scroll:
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the visible glyph layout is window-relative, so adding the full scroll
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maps a tap to a line far below the window (the Phase 7 tap-to-position
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bug). The remainder and the window's start line come from ONE shared
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float64 floor decomposition of `ScrollOffset` (line k, remainder r, with
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k·lineHeight ≤ ScrollOffset < (k+1)·lineHeight): the window starts at
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content line k, the renderer shifts the windowed layout up by r, and a
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tap a dp below the region top maps to content line k +
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⌊(a+r)/lineHeight⌋ = ⌊(a+ScrollOffset)/lineHeight⌋ — the line actually
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under the finger, for every scroll offset (architecture.md §6.2).
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3. **text-local dp → window-relative glyph byte** —
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`visualLine = y / lineHeight`, then glyph x-search within that line
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group. `GlyphLayout.ByteOffsets` are relative to the **top of the
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visible window** (`IMEWindowStartByte`), not the file start.
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4. **window-relative byte → absolute file byte** — add/subtract the window
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base (`IMEWindowStartByte`, the `glyphBase()` helper) at each cursor
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boundary (tap, Home, End, vertical move, selection handles). Forgetting
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this hop is what snapped the cursor to the window top on scrolled files.
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Selection / menu / IME spaces (all app dp unless noted):
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- `EditorState.SelectionStart/End`, `SelectionAnchor`, `CursorPosition`:
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**absolute file bytes** (architecture.md §6.3).
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- `ui.TextField.SelectionStart/End`: **window-relative** bytes into the
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visible `Value` (−1 = none) — rendering + IME use only.
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- `SelectionDragEvent.X/Y`: finger position in **app dp** (renderer reports
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the finger; logic converts, exactly like a tap — §6.3a).
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- `MenuRect`: app dp; `MenuItem.X/Y`: **menu-local** (relative to the menu
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origin — `Menu.Draw` adds the origin back when drawing; a tap is inside
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the menu iff it is inside `MenuRect`, item index =
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`(x − MenuRect.X) / itemW`).
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- IME `key.EditEvent.Range`: **window-relative rune indices** (§6.4).
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Invariants: architecture.md §6.2 (window base), §6.3 (selection/caret),
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§6.3a (touch selection), §6.4 (IME).
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**The tap rule (covers ~95% of needs):** to tap something visible, read its
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(x, y) off the PNG you are looking at, multiply both by **1.2**, and
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`input tap x y`. Screenshot px *are* screen px — no 128 offset involved.
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The 128 offset only matters when converting screen ↔ app-local (e.g.
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predicting which text line a tap will hit, or reasoning about `evtPos`
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values). The app itself is internally consistent — rendering and input
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share the same origin — so the offset only bites at the adb/screenshot
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boundary.
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Fixed geometry (screen px unless noted):
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- status bar: top 128 px; nav bar: bottom 63 px
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- Gboard (no suggestion bar): keyboard top ≈ 1518; rows QWERTY ≈ 1716,
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ASDF ≈ 1880, ZXCV ≈ 2020 (backspace key ≈ (990, 2020)); space/enter
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row ≈ 2168; icon toolbar ≈ 1548. Re-measure from a screenshot if Gboard
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changes.
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- App space (pt): editor region starts at (10, 62); line height 16.8 pt.
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Tap-test pitfalls:
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- The first tap right after launch, file open, or logcat clear is often
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swallowed — re-tap before concluding anything is broken.
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- The first `input text` after a cursor move can silently fail — retype.
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- `input text` goes to whatever has IME focus; if typed text lands in the
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wrong place, suspect cursor/selection state (see the GlyphLayout
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window-relative invariant in `architecture.md`), not tap math.
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- Don't memorize content positions (file rows, buttons) — they drift with
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content. Measure from the current screenshot with the ×1.2 rule.
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## On-device observation loop (quick reference)
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Gio renders into one GL surface, so the authoritative debug signals are
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data, not pixels (use `scripts/emu.sh log|shot|perf|cmd` for the first
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four):
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- `logcat -s pad.pad` — app log (errors, limits, recovery; the normal path
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is quiet by design).
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- `input tap|swipe|text` — drive the UI. **All tap coordinates are screen
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px: read the position off the screenshot, ×1.2** (full reference:
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§Screen coordinates). The first tap right after launch/open is sometimes
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swallowed — re-tap.
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- Autosave debounce is 1 s: **wait ~1.6 s before reading a file back from
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disk** after typing.
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- Memory: `adb shell dumpsys meminfo pad.pad` (watch PSS/RSS; the 3.8 GB
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emulator OOMs the app above ~2.5 GB RSS).
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- Screenshots are an auxiliary check only — state, logcat, and file diffs
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are authoritative.
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