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mobile: smooth-coast - #852

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Oct 26, 2026
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mobile: smooth-coast#852
fizzy-pm[bot] merged 1 commit into
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mobile/smooth-coast

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@fizzy-linux

@fizzy-linux fizzy-linux Bot commented Oct 26, 2026

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Part of fizzyedit/work#362

Goal

Smoother touch coast on mobile (work#362): the content should be at the same place at the same timestamp however the browser cuts the frames.

What changed and why

Fling.step moved by vel * dt and then decayed vel, an Euler step: the distance covered depended on how the clock was cut into frames (about 3% off at 33 ms steps, and different for uneven gaps). It now moves by the exact integral vel * (1 - e^(-k dt)) / k, so position is p0 + v/k * (1 - e^(-k (t - t0))) at each frame's own timestamp. Decay, windowed release speed and thresholds are unchanged. CanvasWidget's pan fling shares Fling.step and gets the same fix.

How it was verified

New test the coast is a function of time, not of how the frames cut it (ScrollArea.zig): the same flick coasted with steady 33 ms frames and with frames alternating 8 and 25 ms, compared at equal timestamps. Fails before (steady vs jittery differ by 0.16 pt at step 1 growing to 1.56 pt at step 14 of 15; e.g. 136.69 vs 135.13), passes after (identical to 0.01 pt: 19.31 / 31.28 / ... / 132.39). Total travel over 0.5 s: 136.7 before, 132.4 after (the true curve; the old Euler step overshot it). The test reads the viewport after the area's deinit (it read it a frame early). Gates: check-fmt, build, test, test-integration, check-web, test-sdk-version, lint, check-tests-reached all pass. Not seen on a phone.

Not done / follow-ups

Causes (2) device-pixel snapping, (3) a refresh per display frame and (4) heavy frames were not measured: this PR fixes only the time-integration cause (1); the code requests a refresh each coasting frame already. If foxnne still sees hitching on the main web build, profile core.profile frames and the snapping next.

Changes (2 files, +33/-4) 
 core/Fling.zig              |  9 ++++++---
 core/widgets/ScrollArea.zig | 28 +++++++++++++++++++++++++++-
 2 files changed, 33 insertions(+), 4 deletions(-)
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 12ms MaxRSS:37M
|     +- 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 12ms MaxRSS:36M
|     +- 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 12ms MaxRSS:36M
      +- 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 13ms MaxRSS:39M
      +- WriteFile . cached
      +- compile lib tree-sitter debug native cached 11ms MaxRSS:39M
      +- 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 6ms MaxRSS:40M
      |     +- options cached
      |     +- options cached
      |     +- options cached
      |     +- run exe generate-def (aarch64.zig) cached
      |     |  +- compile exe generate-def debug native cached 5ms MaxRSS:39M
      |     +- 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 14ms MaxRSS:36M
|     +- 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 cached
|  +- compile test fizzy-plugin-loader-tests debug native cached 14ms MaxRSS:40M
|     +- 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 cached
|  +- compile test fizzy-text-plugin-tests debug native cached 14ms MaxRSS:40M
|     +- 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 cached
   +- compile test fizzy-workbench-plugin-tests debug native cached 13ms MaxRSS:40M
      +- 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 3ms MaxRSS:38M
+- compile obj rehome-fixture-web debug wasm32-freestanding cached 5ms MaxRSS:40M
   +- 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 10ms MaxRSS:36M
   +- 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 5ms MaxRSS:40M
   |     +- options cached
   |     +- options cached
   |     +- options cached
   |     +- run exe generate-def (aarch64.zig) cached
   |     |  +- compile exe generate-def debug native cached 5ms MaxRSS:38M
   |     +- 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-linux @claude
core: touch coast is a function of time, not of frame cuts
eee4522 
Fling.step integrated the decaying speed with an Euler step (speed times
the frame gap, then decay), so the same flick travelled differently on
uneven frame times. It now applies the exact integral over the frame.

Agent-Team: linux
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: smooth-coast
Issue #362: mobile: the touch coast looks hitchy, not smooth (follow-up of #845)
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 (37)
  • 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: 37 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 (eee4522):

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

Updated 2026-10-26 13:28 UTC by the PM. This comment is edited in place.

@fizzy-windows fizzy-windows Bot added reviewing:windows-agy a windows/agy review is running reviewing:windows-codex a windows/codex review is running and removed reviewing:windows-codex a windows/codex review is running reviewing:windows-agy a windows/agy review is running labels 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 12:34
@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 7e517ce Oct 26, 2026
24 checks passed
@fizzy-pm
fizzy-pm Bot deleted the mobile/smooth-coast branch October 26, 2026 14:05
@fizzy-linux fizzy-linux Bot mentioned this pull request Oct 26, 2026
Merged
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