docs: record the Windows A/B of the layer-shader fix

[EtienneLescot]

Summary

Measures the layer-shader fix (#982, #983, #984) on Windows, which the CI only compiles. Hardware: Ryzen 5 7520U, Radeon iGPU, D3D11, h264_amf.

	1.11.0-rc.1	2.0.0-rc.12	2.0.0-rc.13 (= main)
median	34.18 s ± 0.73	116.79 s ± 2.36	35.05 s ± 0.46
local floor	19.83 s	24.42 s	20.54 s
× floor	1.72	4.78	1.71
foreign load	88 %	154 %	72 %

• On Windows the regression was worse than on Linux (4.78× against 2.43×), and the fix brings it back exactly to the 1.11 level.
• rc.13's scoring exports are byte-identical to rc.12's.
• The 3D cursor, the click impact, the device frame with its shadow, the window frame and an animated background are all byte-identical too.
• The two blurred-background variants differ invisibly: PSNR ≥ 67 dB, and the differences are macroblock-shaped.

What changes in the docs:

• rendering-performance.md gets a "The same fix on Windows — 2026-10-03" subsection.
• Its Known gaps bullet is narrowed to what is still unmeasured: Metal, an Intel iGPU, and fxc register counts.
• manual-e2e-checklist.md gets a Partial row in its results log.

Related issue

Refs #982, Refs #983, Refs #984

Type of change

• Documentation

Release impact

• No release note needed

Desktop impact

• Windows

Testing

• cargo test -p openscreen-compositor --lib --tests on the real GPU: 456 passed.
• screen-recorder-benchmark commons-upload / full-demo, three runs in one session, measured on locally extracted app trees. The results are not submitted to the benchmark.
• Variant exports with both builds, compared by md5 and PSNR, plus frames extracted with ffmpeg.
• Preview checks over CDP on a dev build of main. The checks cover background, blur, animation and resize while the background cache is active.

Not run:

• real capture and the HUD (computer-use screenshots were blind);
• Radeon GPU Analyzer register counts;
• an Intel iGPU.

Summary by CodeRabbit

• Documentation
  • Added Windows benchmark results showing the v2.0.0-rc.13 benchmark at 1.71× its local encoder floor, compared with 4.78× for rc.12; scoring exports were byte-identical.
  • Recorded variant-level pixel comparisons, editor-preview checks, and export-path comparisons with earlier builds.
  • Updated outstanding measurement notes, including Intel, register-count, and M1 results; Radeon GPU Analyzer was not run.

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📥 Commits

Reviewing files that changed from the base of the PR and between 7d843ff and fd076ba.

📒 Files selected for processing (1)

• technical-documentation/engineering/rendering-performance.md

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📝 Walkthrough

Walkthrough

The documentation adds Windows export benchmark results for rc.13, compares them with rc.12 and rc.1, and records related export and preview checks. It also updates the list of measurements that remain outstanding.

Changes

Windows export results

Layer / File(s)	Summary
Record benchmark results and remaining gaps technical-documentation/engineering/rendering-performance.md, technical-documentation/testing/manual-e2e-checklist.md	The notes report that rc.13 took 35.05 seconds, compared with 116.79 seconds for rc.12, and that their scoring exports were byte-identical. They also record variant comparisons, preview checks, test results, and outstanding Intel, register-count, and M1 measurements.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Other

Suggested reviewers: my-denia

Merge Risk: 🔵 Low · up to 7d843

The performance record could lead readers to believe every compared output was identical. Clarify that the byte-identical result applies to scoring exports; the remaining issue is limited to the documentation.

Architecture Summary

Architecture risk: 🔵 Low · up to 7d843

The change affects 1 system.

Changed systems: technical-documentation

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — technical-documentation (service) was modified; 2 changed files map to changed impact.

Before / after behavior

• observed — Modified behavior in technical-documentation/engineering/rendering-performance.md: Adds Windows A/B measurements on the reference laptop: rc.12 took 116.79 s (4.78× its local floor), while rc.13 took 35.05 s (1.71×), near rc.1’s 1.72×. It reports byte-identical scoring exports between rc.12 and rc.13, variant-specific output comparisons, preview behavior with the static background cache, and the absence of Radeon GPU Analyzer register counts.
• observed — Modified behavior in technical-documentation/engineering/rendering-performance.md: Replaces the gap stating that D3D11 and Metal shader splits and related cache changes were unmeasured with a Windows measurement: the split, static-background cache, and scissored trail together reduced the reported export cost from 4.78× to 1.71× its local floor with byte-identical pixels. Intel iGPU, fxc register counts, and M1 A/B measurements remain outstanding.
• observed — Modified behavior in technical-documentation/testing/manual-e2e-checklist.md: Adds a results-log entry documenting the Windows export-path slice for issues #982/``#983/``#984, including compositor test results, benchmark comparisons, export and preview checks, and limitations.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the Windows A/B results for the layer-shader fix, which is the main change.
Description check	✅ Passed	The description includes a clear summary, related issues, change type, release and desktop impact, and detailed testing results. The screenshots section is not needed for these documentation-only chan…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at
@technical-documentation/engineering/rendering-performance.md:
- Line 846: Update the Windows A/B sentence to limit the byte-identical claim to
the scoring exports, and keep the blurred-background variant results distinct.
Locate the sentence describing the Ryzen 5 7520U export and its byte-identical
pixels.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: e9e2b39b-6757-4216-86af-f948e6ec8556

📥 Commits

Reviewing files that changed from the base of the PR and between 0624c14 and 7d843ff.

📒 Files selected for processing (2)

• technical-documentation/engineering/rendering-performance.md
• technical-documentation/testing/manual-e2e-checklist.md

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