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fix(miri): pace from where they show the windows of apps focus moves between, and hand slice photos over once shown#91

merged7
miri/v0.5.2
miri/163-focus-and-slices
opened12d agobySSamanyu Das
8 files changed
View on GitHubTwo-way sync enabledPR last imported 11d ago

Refs samanyudas/miri#163. Stacked on #90: the base is miri/163-pacing.

Summary

Two fixes to the pacing from #90.

1. Focus changes between apps. Helium and Beeper can turn slow right after a focus change. Before this, a window whose app kept up through the last motion still counted as prompt, so the window ahead of it ran off and the desktop showed between them.

diff
1 on(focus change)
2+ if focus moves from one app to another
3+ forget what pacing saw of every window of both apps
4+ (they pace from where the window server shows them until they keep up through a whole motion again)

A focus move between two windows of one app forgets nothing. Resetting those too made every window of a one-app row wait a frame for the window behind it (the design reverted in the combined review).

2. Slice photo handover at the shared edge (x = 0). The photo closed when the app had taken the window's move, before the window server showed the window there. The bare desktop flashed where the photo had been.

diff
1 frame
2+ place slice panels, then commit Core Animation at once
3 write window frames
4- photo sliding in: close once the AX write returns
5+ photo sliding in: close once the window server shows its window at rest
6+ (on a frame the sampler read, never on a seed), or after 250 ms

The panels used to be placed after the window writes. A layer-backed panel shows a new frame only at the next run loop pass, so the window ahead could show its move a frame before the photo grew beside it. A lab probe confirmed this, and so did a live run.

Evidence

New harness tests. Each fails on its test commit and passes after the fix:

text
1the_window_ahead_waits_for_a_prompt_window_whose_app_gains_focus
2a_photo_sliding_in_stays_up_until_its_window_shows_where_it_rests
3a_sliding_photo_takes_its_place_before_the_windows_ahead_move

These two guard the timeout and the read snapshot. They pass both before and after the fix:

text
1a_photo_sliding_in_closes_after_a_while_when_its_window_does_not_show
2a_window_counts_as_read_only_once_the_sampler_has_read_it

Checks on this branch:

  • cargo fmt --check passes.
  • cargo clippy -- -D warnings passes.
  • cargo clippy --all-targets -- -D warnings shows the base's 13 pre-existing errors.
  • cargo test passes.

Live on Sam's Mac, 30 October 2026, with fast-release engines. Both builds also have #86. The earlier build is #86 + #87 + #90, and the new build adds this PR. The measurements alternated between the builds in the same session:

measurebeforeafter
desktop between different apps, 4 rounds of 12 presses100 ms in 1 of 4 bursts0 in 4 bursts
switch apps and reverse at once (S1), 10 tries in each of 3 sessionsdesktop in 1/10 each time0/10 each time
slice crossing: frames showing wallpaper in the flash casehandover 3 to 5 ms after the write, before the window could shownone, handover about 19 ms, each on a real read
widest desktop beside a sliding photo1687 pt284 pt
busy app (#86 case), longest pause165 ms112 ms
front window starts moving from rest, median / p90116 / 411 ms107 / 405 ms
time to place p50 / max, overshoot391 / 786 ms, 0392 / 747 ms, 0
quit within 1 s of a move leaves Helium's AXEnhancedUserInterface onyesyes, 3 of 3
stopped app does not stall the rowrecoversrecovers

Costs and what is left:

  • Spotify paused 4 times mid-motion over 40 ms instead of 2, because the windows of the apps that focus moves between now pace from where they show.
  • One burst of 4 showed 33 ms of desktop between two Helium windows. A focus move within one app resets nothing, on purpose.
  • A leaving photo is still paced from where the engine put it. Focusing a stopped app still holds the engine about 0.85 s in AXRaise, in both builds.

The recordings and frame captures stay local for privacy.

Reviewed with sol-loop: 3 rounds with gpt-6.1-sol on high. Sol verdict: approved.

Merge Danger

Door: two-way

A revert restores #90's behavior. The change touches no stored state or config.

Blast Radius: animation

It changes only pacing during row animations and the slice photo handover at the shared edge. If the handover check fails, a photo stays up for at most 250 ms longer.

🤖 Generated with Claude Code

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d931c56
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Added 7 commits

  • fix(miri): pace from where they show the windows of apps that focus moves between2a0079b
  • fix(miri): close a sliding photo only once the window server shows its window at rest3a3ef9b
  • test(miri): keep a sliding photo up until its window shows where it rests813ec43
  • test(miri): pace from where they show the windows of an app that gains focusd77c2f4
  • fix(miri): hand a photo over only on a frame read from the window serverd931c56
  • fix(miri): place a sliding photo before the windows ahead of it movee769404
  • test(miri): place a sliding photo before the windows ahead of it moveef17d95