test(compositor): measure the Glass Lens refraction as an edge shift

[EtienneLescot]

Summary

the_flat_glass_lens_refracts_the_picture now measures the refraction itself. The old moved check counted pixels whose brightness changed under the glass, which the lens lighting alone satisfies: it stayed green with the refraction off (IOR 1.0).

• Renders vertical stripes and their inverse under the lens. The sign of the difference tells which stripe each pixel sees, whatever light the glass adds.
• Edges seen through the lens must sit at least 3 px from every edge of the same row without it, on at least 10 edges.
• Same oracle in the Linux (lavapipe) twin in compositor_linux.rs.

	arrow	pointer
IOR 1.5 (shipped)	23 edges shifted, up to 5.5 px	67 edges shifted, up to 5.5 px
IOR 1.0 (mutant)	0, at most 0.5 px	0, at most 1.0 px

Related issue

Refs #1019 (follow-up to the review nitpick confirmed by @My-Denia).

Type of change

• Bug fix
• Feature
• Enhancement
• Documentation
• Refactor / maintenance
• Performance
• Security

Release impact

• Patch
• Minor
• Major / breaking change
• No release note needed

Desktop impact

• Windows
• macOS
• Linux
• Installer / packaging
• Not platform-specific

Testing

• Windows D3D11, local: cargo test -p openscreen-compositor --test cursor_model_render, 10/10 green. With GLASS_IOR = 1.0 in shaders.hlsl, the new test fails and the old one passes.
• Linux lavapipe (WSL, nix develop .#compositor-view): same numbers as D3D11, and the same red with GLASS_IOR = 1.0 in layer.wgsl.
• CI does not run the Windows render tests (cargo check only); the Linux twin runs in rust-linux-compositor-check.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Tests
  • Updated Glass Lens rendering checks to measure how far visible stripe edges shift through the lens, replacing the previous brightness-change pixel count.
  • Added coverage for light-and-dark stripe patterns to improve verification of lens refraction across rendered images.

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: defaults
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• Run ID: c0633093-1173-4e3a-90a7-bb5f54ae5d39

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📥 Commits

Reviewing files that changed from the base of the PR and between ad51125 and 8743d0f.

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📒 Files selected for processing (2)

• crates/compositor/src/compositor_linux.rs
• crates/compositor/tests/cursor_model_render.rs

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📝 Walkthrough

Walkthrough

The Glass Lens render tests now use normal and inverted stripe patterns to measure edge displacement. Both tests require at least 10 stripe edges to shift by 3 pixels or more through the lens.

Changes

Glass Lens render tests

Layer / File(s)	Summary
Stripe-edge detection helpers crates/compositor/src/compositor_linux.rs, crates/compositor/tests/cursor_model_render.rs	The test helpers generate normal and inverted stripe patterns and detect luminance transitions in retained pixels.
Lens displacement measurement crates/compositor/src/compositor_linux.rs, crates/compositor/tests/cursor_model_render.rs	Both Glass Lens tests compare in-lens stripe edges with bare-screen edges. They replace the displaced-pixel count with a requirement that at least 10 edges shift by 3 pixels or more.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Other

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Merge Risk: ⚪ Minimal · up to 8743d

The changed tests target stripe-edge displacement, and no concrete issue is established that would prevent merging after normal checks.

Pre-merge checks | 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: measuring Glass Lens refraction through edge shifts.
Description check		The description is complete and relevant. It explains the change, related issue, change type, release impact, platform impact, and testing results. The optional Screenshots / video section is not fill…
Docstring Coverage		Docstring coverage is 90.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 10 functions across 2 files.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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[EtienneLescot]

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