Chromium's native touch selection cannot be used in the columned
layout: quick taps select words, the word iterator re-anchors at
page boundaries (jumping to other pages), and the browser
auto-scrolls the container when selections cross pages.
preventDefault on touchstart disables it; long-press selects the
word under the finger, drag extends word by word clamped to the
visible page, and pan/snap stand down while a selection gesture is
active. Native rendering still paints the selection.
Mobile browser toolbar transitions change the viewport height by a
fraction mid-gesture; re-rendering for them re-wraps the whole book
and reads as a page refresh. Re-render only for width changes or
height changes of 25% or more.
The custom gesture system and the selection clamp/repair chain
replaced browser behavior with worse approximations. Keep only the
non-touch gate on selection auto-paging (de70103), which fixes
drag-selecting paging away mid-gesture; everything else returns to
upstream behavior.
Chrome's native touch selection misbehaves in the paginated column
layout: quick taps select words, and dragging from a line-start word
re-anchors at a rendered line break, dropping the word and freezing
the gesture. preventDefault on touchstart disables it entirely; a
long-press timer selects the word under the finger instead and drag
moves extend word by word, clamped to the visible page and identical
for every word. Clean taps clear the selection or follow links
(click events being suppressed by the preventDefault).
A selection write at the moment Chrome re-anchors the drag detaches
its touch selection controller; the same writes on a settled
selection are fine. Record the word synchronously, repair only when
the selection has been unchanged for 150ms.
Rewriting both selection boundaries mid-gesture detaches Chrome's
touch selection controller and the selection stops following the
finger. extend() moves only the focus, which the controller
tolerates.
Dragging just past a line-start word makes Chrome flip the touch
selection and re-anchor it at a rendered line break, silently
dropping the long-pressed word from the selection. Record the word
at the initial long-press and restore its start boundary whenever
the selection no longer covers it.
The helper created its probe range in the module's own document
(the host, in the bundled web reader), so boundary points in the
content iframe collapsed the range and every selection read as
backward.
The last visible range can extend past the visible column on text
nodes that span multiple columns (its end-offset bisect uses union
rects), so comparing DOM boundary points against it misses off-view
selection endpoints. Test the endpoint caret rect against the
visible column bounds instead.
Chrome emits collapsed selectionchange events while the long-press
word selection is being set up; clearing the flag on them disarmed
the clamp before the selection ever became a Range.
Chrome word-snapping during a touch selection drag can map the
endpoint past the visible column into the next (off-screen) page,
selecting the entire visible page at once. Re-map the endpoint via
caretRangeFromPoint at the same line height inside the visible
column whenever it lands outside the last visible range.
John O'Keefe