komorebi/docs/dev/scrolling-next.md

The rework of the Scrolling layout on upstream's next

Upstream (LGUG2Z/komorebi) reworked the Scrolling layout on its next branch: a platform-free model of a strip of columns (komorebi-scrolling), the glue that every komorebi shares (komorebi_layouts::scrolling), and, on top of them, columns that hold several windows and the commands that go with them. This page says, for each of the commits of master...next that touch the layout, what it changes, whether komorebi for KDE (kfde) takes it, and how. The review is of next at 6d862a114 (the revision kfde's Cargo.toml pins now).

Two things shape what applies. The model and the platform-free glue live in crates that kfde takes from upstream by git revision, as it already took komorebi-layouts, so a commit that only touches them arrives with the bump of the revision. And what the glue needs of a window (where it is, whether it is hidden, how wide it really is) is a call to the backend in kfde, not to Win32.

Commits of the layout

Commit	What it changes	kfde
9ccf2efce model of a scrollable strip	New crate komorebi-scrolling: columns of tiles, widths (proportion or fixed, limits), heights, view offset, centring (Never, Always, OnOverflow), pan, swipe tracker. No Windows code. Tests in the crate.	Ported by dependency. komorebi-scrolling is a git dependency at the same revision as the layouts. Its tests are upstream's; kfde tests the glue.
abd4fde3e lay out with the model	The workspace keeps a ScrollingSpace keyed by container id; update() places containers from it instead of recomputing equal columns from the last layout.	Ported (komorebi/src/scrolling.rs, Workspace::update).
cb127204c platform-free glue	komorebi_layouts::scrolling (options, place, resize, hand-over between workspaces), ScrollingCentering replaces the bool of center_focused_column; Workspace methods for focus, order, consume, expel, stack.	Ported: the layouts half by the bump, the Workspace half in komorebi/src/scrolling.rs.
249709e60 commands and config	Socket messages and komorebic commands consume, expel, toggle-column-stack, scrolling-layout-full-width, center-focus, expand; focus, move, resize, retile and close go through the strip. The message says a top level scrolling section too.	Ported, except the scrolling section: neither kfw nor kfde has one (only komorebi for Mac has; COMPARE.md says so).
9ff278eb5 schemas	center_focused_column is a boolean or a name; docs for the new commands; schema.bar.json.	Ported: schema.json, nix/komorebi-options.nix, docs/cli/. schema.bar.json is kfw's (kfde has no bar).
2dff53095 room for windows that will not get narrow	After windows are placed, a window wider than its column widens the column (never narrower again, never wider than the screen), for an overhang of 16 px or more.	Ported, with a different trigger. kfde cannot ask a window how wide it is right after moving it: the frame comes back from KWin a moment later. The widths are read at the first layout after the frames have settled (WIDTH_SETTLE), as upstream does with animations on. Covered by unit tests in scrolling.rs; no VM check, because it needs a client that will not get narrower and foot has no minimum width.
e75f3db47 rest windows at the edge	A window out of view rests at the edge it left by with 5 px on screen and keeps its size.	Ported (parked). On KDE this also keeps the window from being resized while it moves out of view, which is what KWin pulls back (PLATFORM.md).
ab1896330 docs	docs/usage/scrolling-layout.md, mkdocs.yml.	Ported, rewritten for KDE (no animation, no borders at the edges, no touchpad).
1531a892a more than one monitor	Removes the single-monitor restriction; a window out of view past an edge with a monitor next to it is hidden, not parked; a partly visible one is cut to its work area; a window that comes back is shown first, only the one at the front of a stack.	Ported (rest, other_monitors, should_restore_when_placed, from backend().monitors() and Window::hide). kfde never had the restriction. This answers the open question in PLATFORM.md about a strip that spills onto the next monitor.
abb230b45 spread a stack out	The window that stays in the container is restored; focus stays on the column while the containers are inserted.	Ported.
ca22b0f81 refocus after Hide	The Hide event arm refocuses like Destroy.	Not applicable. kfde has no Hide event: KWin reports a closed window as a destroyed one, which already refocuses.
f2b72a029, f22560464 left edge	Resizing a column by its left edge moves that edge, however far.	By the bump (komorebi_layouts::scrolling::resize). kfde's drag of an edge goes through the same function, and LiveResize keeps the strip (below).
1f658fd90 pan	komorebic pan left|right moves the view a column.	Ported.
09b99700f touchpad	pan --stream reads whkd's gesture stream; PanGesture, swipe tracking, pictures over the windows.	Not applicable. whkd and the raw touchpad input are Windows only. The swipe tracker is in the model crate if a KDE input path wants it later.
674ae7937, 5098ff7b7 resize follows the drag	The neighbours follow a dragged edge; the strip is kept with the rest of what the drag started from.	The strip part ported: LiveResize keeps and restores Workspace::scrolling, or every step of a drag would compound on the widths of the one before. The pictures over windows are DWM.
ce13267e1, 62628f381, 2a447208f, 58693ecd3, 52ad6be78	Where a drag is measured from; pictures and ghosts for windows being resized or animated.	Not applicable. Ghost windows and DWM. kfde measures a drag from Backend::drag_origin already.
e5512ca5d and the other animation and border commits	Ghosts, workspace slide, border in ghosts, batches of animations.	Not applicable (DWM, ghost windows, borders). The Windows session's.
3b424dd70, 837ca257d, 5c8e4770d, 9b9cad997	Fixes in config, monitors, rules.	Not scrolling. Already in kfde or in the hands of the other sessions.

What I could not judge

• Whether the 5 px of a parked window pass KWin's rule of keeping 100 px of a resized window on an output. The bridge's settle asks again for a position up to three times, and a parked window is not resized to be parked, but only the VM says.
• Whether Window::hide of a column that scrolls out of view next to another monitor is fast enough to follow a scroll without a flash. It is what stacks do.
• The 16 px tolerance of 2dff53095 against the clients of client-geometry (foot rounds to cells, which is below it).

What is tested, and where

• komorebi/src/scrolling.rs: the glue against a workspace with no desktop (widths, consume, expel, moving a column, stacking and spreading out with the windows that are hidden, expanding, panning, where a window rests, which monitors are the others, what a window that will not get narrow says). The model itself has its tests in upstream's komorebi-scrolling.
• komorebi/tests/scrolling.rs and layout_options.rs: the commands through WindowManager::process_command against the fake desktop, a strip next to another monitor, and a drag of the left edge of a column.
• komorebic/tests/cli.rs: each new subcommand sends its message.
• nix/tests/vm/lib/komorebi_vm/core/scenarios/scrolling.py (columns, shared with komorebi for Windows), run by vm-scrolling and core-e2e: where the daemon keeps a window at the edge and the commands of the columns, in a real session. Run on KDE: the scrolling suite passes (32 checks, with two_monitors). KWin leaves a window resting at the left edge with its right edge a few pixels inside the work area, or a cell short of them, because foot rounds its frame to whole cells. The shared scrolling scenario passes in core-e2e too.