The first grab implementation degraded Shift+grab to a quarter-speed
relative crawl — losing the ±5-minute rail the user expects when they
grab the handle with Shift held. The rail is back: Shift+grab anchors
railWindow at the CURRENT position (not the nearest chapter line, and
never teleports the playhead on pointerdown); plain grab stays relative
1:1. GRAB_FINE_SCALE is deleted as dead code, and the dialog guide
documents the restored gesture.
A pointerdown on the scrub bar unconditionally mapped the click X to a
position, so grabbing the handle itself made the playhead jump — worst
with Shift, whose branch force-snapped to the nearest chapter line
before the drag even started. The user's complaint: the handle click
flowed through to the track-click behavior behind it.
The bar now hit-tests the thumb first (GRAB_SLOP_PX, a pixel test like
the chapter magnetism — a seconds threshold goes sub-pixel on long
books). A grab enters a new "grab" drag mode: the position stays where
it is until the pointer moves, then advances RELATIVELY via the new
applyGrab helper (incremental like the touch cursor, fixed scale — the
mouse is always on the bar, so Shift = quarter-speed fine crawl instead
of a pull-away zoom).
Track clicks keep today's behavior exactly: click = jump with chapter
magnetism, Shift+click = nearest chapter line, Shift+drag = precision
rail, touch = incremental pull-away. MOUSE_GUIDE gains the two grab
rows so the dialog documents the gesture; new pure helpers are unit-
tested alongside the existing scrub math.
Mouse: drag is free-flow 1:1 (rail only on Shift+drag, now with
window from/to edge labels); clicks land with pixel magnetism
(MAGNET_RADIUS_PX=10) — the old 5-second threshold was sub-pixel on
long books and never fired, which was the 'chapter scrub isn't
accurate' bug. Hover inside the radius locks the tooltip to the line
with a highlight. Shift+click jumps to the nearest line from anywhere.
Touch: drag is an incremental cursor (applyDrag) whose scale tightens
continuously as the finger pulls off the bar (dragScale, exponential
10^(-|dy|/80px)) — the rail is the feedback: window shrinks with the
zoom (touchRailSpan) and lifts toward the finger (railLiftPx).
Dialog retitled 'Shortcuts & interactions' with a Mouse & touch
section driven by POINTER_GUIDE (audio-keys.ts). Old seconds-threshold
snapToChapter deleted. 133 unit tests; 19 Playwright checks on the
KJV (1189ch) and Gardens (34ch) books.
The scrubber becomes a layered bar: the native <input type=range> stays
on top for a11y (focus, arrow keys, aria — its track goes transparent
via static page CSS) while the layers beneath render the state:
- Chapter ticks: density-decimated (denseTicks keeps only marks >= 4px
apart) so an 1189-chapter 86-hour book gets ~100 readable marks
instead of a solid mass; the current chapter's tick is tinted.
- Buffered span: the ACTIVE track's buffered-ahead end mapped into the
global bar (buffers are per-track and never span the whole bar).
bufferedAheadEnd reads the range containing the playhead — a huge
m4b's moov index at the file tail is its own buffered range and must
not read as 'the whole book is buffered'. Rides progress + the
events that demonstrably fire for Range-served files that go
network-idle while paused (timeupdate/canplay/loadedmetadata/playing).
- Wheel over the bar: ±5s nudge, Shift = ±60s.
- Hover tooltip: time + chapter title under the pointer.
- Precision rail: while dragging, a ±5-minute window floats below the
bar (fixed anchor; release and re-grab to travel far) and the drag
maps at minutes-per-pixel instead of hours-per-pixel — the whole
point for 80h+ books. Click snaps to a chapter line within ~5s
(snapToChapter).
Pointer handling is ours end-to-end: pointerdown maps hours-per-pixel
+ snaps, captured moves remap through the rail, release seeks. The
native drag default is prevented so the two mappings never fight;
keyboard arrows keep their native step and seek via change.
Time labels get reserved width — the bar no longer resizes when the
elapsed label grows from 0:00 to 43:07 mid-drag (caught by the rail
drag check measuring a 25% mapping drift).
Pure math in audio-scrubber.ts: pointer mapping, chapter lookup, snap,
tick density, per-track buffer→global span, rail window/mapping/ticks.
Unit: 16 new tests including both book shapes (86h/1189ch and
26h/34ch). Live: 23 Playwright checks on KJV (folder) and Gardens of
the Moon (single-file m4b); zip books share the folder manifest shape
(no zip fixture exists in the dev library). Probe user deleted.
John O'Keefe