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mobile: coast-frame-pacing - #854

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mobile/coast-frame-pacing
Oct 26, 2026
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mobile: coast-frame-pacing#854
fizzy-pm[bot] merged 1 commit into
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mobile/coast-frame-pacing

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@fizzy-macos fizzy-macos Bot commented Oct 26, 2026 •
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Part of fizzyedit/work#362

Goal

A touch coast glides to a stop instead of stepping: its slow tail moves a fraction of a pixel a frame, and dvui's snap_to_pixels drew it at whole pixels (a 1 px step every few frames).

What changed and why

core/widgets/ScrollArea.zig: while either axis coasts, the area turns snap_to_pixels off from init to deinit, so its content draws at the fractional offset. deinit puts the setting back, so the first frame after the coast ends is snapped and text is crisp at rest. Decay, windowed release speed and the time-based step are untouched.

How it was verified

New test "a slow coast draws at a new place every frame, then snaps at rest" (120 fps frames, 25 to 60 pt/s tail): fails without the change (zb build test-integration: 740/741, the drawn y repeats), passes with it. Drawn displacement per frame at 51 pt/s: before -1, -1, -1, 0 px (whole-pixel steps); after -0.83, -0.79, -0.76, ... -0.47 px at 29 pt/s (fractional, never repeating). Measured in the headless dvui test window only (scale 1), not on a device; foxnne checks on the testapp. Gates run: check-fmt, build, test, test-integration, check-web, test-sdk-version, lint.

Not done / follow-ups

Firefox's 60 Hz rAF cap and heavy frames during a coast (items 1 and 4 of the issue) are not touched; see linux/claude's note on the issue. No on-device numbers.

Changes (1 files, +43/-1) 
 core/widgets/ScrollArea.zig | 44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)
Gates: 6 of 6 passed

scripts/check-fmt.sh (exit 0)

check-fmt: listing tracked files
check-fmt: checking 535 files

scripts/zb build --summary all (exit 0)

... (earlier output omitted)
|     +- compile lib tree-sitter debug native (reused)
|     +- compile lib freetype debug native (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- options (reused)
|     +- options (reused)
|     +- translate-c dvui-c cached
|     |  +- compile exe translate-c debug native (+21 more reused dependencies)
|     +- options cached
|     +- options cached
+- install text cached
|  +- compile lib text debug native cached 66ms MaxRSS:31M
|     +- WriteFile plugin_root.zig cached
|     +- WriteFile freetype (reused)
|     +- compile lib freetype debug native (reused)
|     +- WriteFile . (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- compile lib freetype debug native (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- options (reused)
|     +- translate-c dvui-c (+1 more reused dependencies)
|     +- options (reused)
|     +- options (reused)
+- install markdown cached
|  +- compile lib markdown debug native cached 65ms MaxRSS:31M
|     +- WriteFile plugin_root.zig cached
|     +- WriteFile freetype (reused)
|     +- compile lib freetype debug native (reused)
|     +- WriteFile . (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- compile lib freetype debug native (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- options (reused)
|     +- translate-c dvui-c (+1 more reused dependencies)
|     +- options (reused)
|     +- options (reused)
|     +- translate-c (reused)
+- install image cached
   +- compile lib image debug native cached 66ms MaxRSS:31M
      +- WriteFile plugin_root.zig cached
      +- WriteFile freetype (reused)
      +- compile lib freetype debug native (reused)
      +- WriteFile . (reused)
      +- compile lib tree-sitter debug native (reused)
      +- compile lib freetype debug native (reused)
      +- compile lib tree-sitter debug native (reused)
      +- options (reused)
      +- translate-c dvui-c (+1 more reused dependencies)
      +- options (reused)
      +- options (reused)

scripts/zb build test --summary all (exit 0)

... (earlier output omitted)
      +- WriteFile freetype cached
      +- compile lib freetype debug native cached 79ms MaxRSS:31M
      +- WriteFile . cached
      +- compile lib tree-sitter debug native cached 60ms MaxRSS:30M
      +- compile lib freetype debug native (reused)
      +- compile lib tree-sitter debug native (reused)
      +- translate-c dvui-c cached
      |  +- compile exe translate-c debug native cached 94ms MaxRSS:31M
      |     +- options cached
      |     +- options cached
      |     +- options cached
      |     +- run exe generate-def (aarch64.zig) cached
      |     |  +- compile exe generate-def debug native cached 85ms MaxRSS:31M
      |     +- run exe generate-def (amdgcn.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (arm.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (bpf.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (common.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (hexagon.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (loongarch.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (mips.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (neon.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (nvptx.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (powerpc.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (riscv.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (s390x.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (ve.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (wasm.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (x86_64.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (x86.zig) cached
      |     |  +- compile exe generate-def debug native (reused)
      |     +- run exe generate-def (xcore.zig) cached
      |        +- compile exe generate-def debug native (reused)
      +- options cached
      +- options cached

scripts/zb build test-integration --summary all (exit 0)

... (earlier output omitted)
|     +- options (reused)
|     +- options (reused)
+- run test fizzy-glass-tests cached
|  +- compile test fizzy-glass-tests debug native cached 273ms MaxRSS:31M
|     +- WriteFile freetype (reused)
|     +- compile lib freetype debug native (reused)
|     +- WriteFile . (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- compile lib freetype debug native (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- translate-c dvui-c (+1 more reused dependencies)
|     +- options (reused)
|     +- options (reused)
+- run test fizzy-plugin-loader-tests 2 pass (2 total) 130ms MaxRSS:3M
|  +- compile test fizzy-plugin-loader-tests debug native success 6s MaxRSS:366M
|     +- WriteFile freetype (reused)
|     +- compile lib freetype debug native (reused)
|     +- WriteFile . (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- compile lib freetype debug native (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- translate-c dvui-c (+1 more reused dependencies)
|     +- options (reused)
|     +- options (reused)
+- run test fizzy-text-plugin-tests 101 pass (101 total) 1s MaxRSS:24M
|  +- compile test fizzy-text-plugin-tests debug native success 8s MaxRSS:718M
|     +- options (reused)
|     +- WriteFile freetype (reused)
|     +- compile lib freetype debug native (reused)
|     +- WriteFile . (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- compile lib freetype debug native (reused)
|     +- compile lib tree-sitter debug native (reused)
|     +- translate-c dvui-c (+1 more reused dependencies)
|     +- options (reused)
|     +- options (reused)
+- run test fizzy-workbench-plugin-tests 1 pass (1 total) 133ms MaxRSS:3M
   +- compile test fizzy-workbench-plugin-tests debug native success 2s MaxRSS:317M
      +- options (reused)
      +- options (reused)
      +- WriteFile freetype (reused)
      +- compile lib freetype debug native (reused)
      +- WriteFile . (reused)
      +- compile lib tree-sitter debug native (reused)
      +- compile lib freetype debug native (reused)
      +- compile lib tree-sitter debug native (reused)
      +- translate-c dvui-c (+1 more reused dependencies)
      +- options (reused)
      +- options (reused)

scripts/zb build check-web --summary all (exit 0)

... (earlier output omitted)
|  |     +- run exe generate-def (amdgcn.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (arm.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (bpf.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (common.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (hexagon.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (loongarch.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (mips.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (neon.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (nvptx.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (powerpc.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (riscv.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (s390x.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (ve.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (wasm.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (x86_64.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (x86.zig) cached
|  |     |  +- compile exe generate-def debug native (reused)
|  |     +- run exe generate-def (xcore.zig) cached
|  |        +- compile exe generate-def debug native (reused)
|  +- options cached
|  +- options cached
|  +- options cached
|  +- options cached
|  +- options cached
|  +- options cached
|  +- options cached
|  +- options cached
|  +- options cached
|  +- options cached
|  +- translate-c cached 27ms MaxRSS:30M
+- compile obj rehome-fixture-web debug wasm32-freestanding cached 42ms MaxRSS:31M
   +- translate-c dvui-c (+1 more reused dependencies)
   +- options (reused)
   +- options (reused)

scripts/zb build test-sdk-version --summary all (exit 0)

... (earlier output omitted)
   +- WriteFile . cached
   +- compile lib tree-sitter debug native cached 42ms MaxRSS:30M
   +- compile lib freetype debug native (reused)
   +- compile lib tree-sitter debug native (reused)
   +- options cached
   +- options cached
   +- translate-c dvui-c cached
   |  +- compile exe translate-c debug native cached 41ms MaxRSS:31M
   |     +- options cached
   |     +- options cached
   |     +- options cached
   |     +- run exe generate-def (aarch64.zig) cached
   |     |  +- compile exe generate-def debug native cached 44ms MaxRSS:31M
   |     +- run exe generate-def (amdgcn.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (arm.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (bpf.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (common.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (hexagon.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (loongarch.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (mips.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (neon.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (nvptx.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (powerpc.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (riscv.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (s390x.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (ve.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (wasm.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (x86_64.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (x86.zig) cached
   |     |  +- compile exe generate-def debug native (reused)
   |     +- run exe generate-def (xcore.zig) cached
   |        +- compile exe generate-def debug native (reused)
   +- options cached
   +- options cached

@fizzy-macos @claude
mobile: draw a coast at the fractional offset
6d717c4 
Part of fizzyedit/work#362

Agent-Team: macos
Worker: claude

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
@fizzy-pm

fizzy-pm Bot commented Oct 26, 2026

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PM note: how this PR will be handled

What it is for: mobile: coast-frame-pacing
Issue #362: mobile: animations and the coast run at 60 fps on a 120 Hz display (frame pacing)
Done when (from the issue): one PR with the test, numbers in the body; foxnne checks on the main web build.

Rules that apply: none special.
Reviews needed: 1, from any other team or kind.
Needs the maintainer's explicit yes before merge: no

Things to watch (checked by rule):

  • the body names its work issue (Part of fizzyedit/work#N)
  • size within 800 lines outside tests and docs (44)
  • a gates section with what was run

What happens next:

  1. Reviewers from other teams or kinds comment, with findings numbered F1, F2, ...
  2. The author answers every finding in one FIXES @<commit> comment (fixed in a commit, or declined with a reason) and pushes.
  3. Reviewers re-review the new commit on their own.
  4. When every finding is answered and the re-reviews are clean, the PM marks it ready and the full CI runs (a few times at most: run the failing job locally before you push again). Only when CI passes does the PM look, and the PM gives the final okay.

A living status comment below is kept current. Nothing here is a merge decision.

@fizzy-pm

fizzy-pm Bot commented Oct 26, 2026 •
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Where this PR stands

Stage: Done: approved
Next: Waiting for the merge queue

What the PM needs before approving (ticks as it is met; the full CI runs only at the end, after the reviews are clean):

  • The body names its basis (Part of fizzyedit/work#N or a plan step)
  • Within the size limit: 44 of 800 lines outside tests and docs
  • The body shows which gates the author ran
  • No open findings at this commit
  • Every earlier finding was answered in a FIXES comment
  • Clean reviews at this commit from 1 kind: linux/codex (has 1)
  • Marked ready, which starts the full CI (the PM does this the moment the items above are met)
  • The full CI passes at this commit (CI is green)
  • The PM's final okay (pm-approval)

Reviews at the current commit (6d717c4):

Reviewer Verdict Findings
linux/codex clean none
windows/codex inconclusive none

Updated 2026-10-26 16:15 UTC by the PM. This comment is edited in place.

@fizzy-windows fizzy-windows Bot added the reviewing:windows-codex a windows/codex review is running label Oct 26, 2026
@fizzy-linux fizzy-linux Bot added reviewing:linux-codex a linux/codex review is running reviewing:linux-agy a linux/agy review is running and removed reviewing:linux-codex a linux/codex review is running reviewing:linux-agy a linux/agy review is running labels Oct 26, 2026
@fizzy-windows fizzy-windows Bot removed the reviewing:windows-codex a windows/codex review is running label Oct 26, 2026
@fizzy-pm fizzy-pm Bot added pm:review one assigned reviewer reviews reviewer:linux-codex the PM assigned linux/codex to review this PR labels Oct 26, 2026
@fizzy-linux fizzy-linux Bot added reviewing:linux-codex a linux/codex review is running and removed reviewing:linux-codex a linux/codex review is running labels Oct 26, 2026
@fizzy-pm
fizzy-pm Bot marked this pull request as ready for review October 26, 2026 15:37
@fizzy-linux fizzy-linux Bot removed the reviewing:linux-codex a linux/codex review is running label Oct 26, 2026
@fizzy-pm fizzy-pm Bot removed pm:review one assigned reviewer reviews reviewer:linux-codex the PM assigned linux/codex to review this PR labels Oct 26, 2026
@fizzy-pm
fizzy-pm Bot added this pull request to the merge queue Oct 26, 2026
Merged via the queue into main with commit b32bcf2 Oct 26, 2026
28 checks passed
@fizzy-pm
fizzy-pm Bot deleted the mobile/coast-frame-pacing branch October 26, 2026 16:41
@fizzy-linux fizzy-linux Bot mentioned this pull request Oct 26, 2026
Merged
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