Let half actions preserve the window's size on the other axis (opt-in)

[X-Wei]

Summary

Adds an opt-in mode in which Left Half, Right Half, Top Half and Bottom Half only change the axis they belong to (Left/Right → width, Top/Bottom → height) and keep the window's size and position on the other axis — the way Win + arrow keys tile windows on Windows, or keyboard tiling works on KDE.

With it, the four half shortcuts are enough to reach every half and quarter: Left Half then Top Half lands in the top left quarter, Bottom Half from there expands back to Left Half, and Right Half then Left Half fills the screen.

Off by default (halvesPreserveOtherAxisSize); nothing changes unless it is enabled.

Related: discussions #665 and #811 (where this was asked for, and you said you would be fine merging a good PR for it configurable via Terminal command), and #144. This is the narrow version discussed there: no separate "Windows mode" and no preset or extra shortcuts — the existing half actions simply take the window's current position into account, the logic lives in one self-contained class, and everything sits behind a single default.

Behavior when enabled

Each half action looks at where the window currently sits along its own axis and leaves the other axis exactly as it is:

Window along the action's axis	Left Half / Top Half	Right Half / Bottom Half
spans the whole axis (or has a size no half action produces)	dock to the left / top edge	dock to the right / bottom edge
docked to the left / top edge	inside a quarter: no change; plain half: repeats as today (cycle sizes, move across displays, …)	expand to the whole axis
docked to the right / bottom edge	expand to the whole axis	inside a quarter: no change; plain half: repeats as today

Some sequences:

Sequence	Result
Left Half, Top Half (or Top Half, Left Half)	top left quarter
top left quarter, Bottom Half	Left Half
top left quarter, Right Half	Top Half
top left quarter, Top Half or Left Half	no change
Right Half, Left Half	full width and height (same as Maximize, including its gap setting)
Left Half, Left Half	as today: cycle 1/2 → 2/3 → 1/3, move across displays, or nothing, depending on the repeated-command setting
untiled (floating, centered, …) window, any half	as today

Untiled windows and repeated executions of a plain half deliberately fall through to the existing code, so the feature never changes what the repeated-command setting does.

How it works

• HalvesPreserveOtherAxisSize.rect(for:) recognizes the window's state on each axis purely from its current frame: an axis counts as "docked" when the window's origin and extent match (within 10 pt, for apps that resize in character cells) an edge-docked rect that a half action produces on that screen — at the active split ratio or any cycle size, with or without gaps applied. Anything else counts as "whole axis". It returns nil whenever the existing logic should run.
• LeftRightHalfCalculation, TopHalfCalculation and BottomHalfCalculation consult it first when the default is enabled; otherwise they are untouched.
• The result reports the geometrically equivalent action (.topLeft + .topLeftQuarter, .leftHalf, .maximize, …) as resultingAction / subAction, so gaps and the window history behave exactly as if that action had been executed. For that, WindowCalculation.calculate now forwards RectResult.resultingAction instead of ignoring it — every subclass that sets it already overrides calculate, so this is not a behavior change by itself.
• Drag to snap goes through the same calculations, so the footprint preview matches the snap. With the default unsnap-restore the dragged window is back at its original size when it snaps, so snapping behaves as before.

Testing

• HalvesPreserveOtherAxisSizeTests (32 cases): every state transition, no-ops inside quarters, fallback to the existing logic for untiled windows and repeated plain halves, cycled 2/3 and 1/3 columns/rows, non-50 % split ratios, gaps (including the skip-top-edge option), matching tolerance, and the disabled path.
• Full suite on top of 64a9186 (v0.99): 266 tests, 0 failures.
• Used daily on macOS 26.6 since 2026-08-21 with 5 px gaps, 50 % splits and the default repeated-command setting (resize).

Try it

A notarized Apple-silicon build of this branch (unofficial, signed with my own Developer ID) is attached to https://github.com/maxing-labs/Rectangle/releases/tag/v0.99-halvesPreserveOtherAxis-b108 — install, then tick the checkbox at the bottom of the Extras popover in Settings.

Docs / UI

• TerminalCommands.md: new section "Make the half actions tile like Windows or KDE" with the defaults write command.
• Settings gets a "Half actions preserve the window's size on the other axis" checkbox, unchecked by default, at the bottom of the Extras popover in the General tab (below the side split ratio rows, as requested), with a tooltip describing the Left Half → Top Half → Bottom Half round trip; the two strings are registered in Main.xcstrings. Happy to drop the checkbox and keep this terminal-only if you prefer.

[rxhanson]

Thanks for contributing! Things look good at a quick glance. The list of checkboxes in the General tab is steadily growing and I haven't ironed out my preferred way to prevent it from turning into something unwieldy. Would you mind putting that checkbox at the bottom of the popover displayed from the "Extras" button in the General tab for now? I think I'll end up with another tab for more settings instead of the Extras button, but I haven't decided where everything will go yet.

[X-Wei]

Done — the checkbox now sits at the bottom of the Extras popover, below the side split ratio rows, and the General tab is untouched. Same title, tooltip and default (off); the commit is amended and force-pushed. Happy to move it again once you settle on a tab for these.