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test(gui): golden sheet for COLRv1 emoji cell averages - #552
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The hue assertions in the emoji test answer whether a cell is painted; they cannot see how. The regressions that mattered — a clip applied to its own fill, a dropped paint transform — moved edge coverage, which barely moves a hue but moves a cell average. Cell averages are also stable across renderers, unlike pixel-exact images. Four COLRv1 emoji at one size, one box average per glyph, compared against a committed golden with a three-level per-channel tolerance. NEOMACS_GOLDEN_UPDATE=1 regenerates the golden; the sheet stays at four glyphs because the readback diagnostics report at most four boxes. Verified: the comparison is green, a ten-level perturbation fails with the exact channel delta and a regeneration hint, and regenerating restores green.
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📝 Walkthrough
Merge Risk: 🔵 Low · up to The test is mergeable with a bounded risk: a runner setting the update variable to 0 would replace the baseline instead of checking it. Require the documented value 1 to avoid that surprise. Pre-merge checks |
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| Check name | Status | Explanation |
|---|---|---|
| Title check |  |
The title clearly summarizes the main change: adding a GUI golden sheet test for COLRv1 emoji cell averages. |
| Description check | |
The description directly explains the motivation, fixture, comparison logic, tolerance, regeneration method, and validation for the changeset. |
| Docstring Coverage | |
Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 1 files. (2 skipped: 2 … |
| 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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Actionable comments posted: 1
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Inline comments:
Review comments at @crates/neomacs-gui-tests/tests/golden_emoji_sheet.rs:
- Line 133: Update the update-mode check in the golden sheet test so it
activates only when NEOMACS_GOLDEN_UPDATE is set to the documented value 1;
other values, including 0, must continue to the comparison path.
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📒 Files selected for processing (3)
crates/neomacs-gui-tests/fixtures/golden-emoji/init.elcrates/neomacs-gui-tests/fixtures/golden-emoji/sheet.jsoncrates/neomacs-gui-tests/tests/golden_emoji_sheet.rs
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🔵 Needs a closer look
The golden uses a tight ~3/255 per-channel tolerance on GPU surface-readback averages generated on one machine, and its cross-environment stability on differing CI rasterizers cannot be verified here, so a human should confirm it will not be flaky.
0 open findings
What changed in this PR
This PR adds a GUI "golden sheet" test that guards against COLRv1 emoji rendering regressions that the existing colrv1_emoji hue assertions cannot detect (e.g. a clip applied to its own fill, or a dropped paint transform). These regressions barely move a cell's hue but shift edge coverage, which does move the cell's RGBA average. Because per-glyph cell averages are the surface readback's own statistic and are more stable across GPUs/drivers than pixel-exact images, the test records four emoji cell averages and compares them against a committed golden with a three-level per-channel tolerance, regenerable via NEOMACS_GOLDEN_UPDATE=1.
Changes:
- New fixture
init.eldraws four COLRv1 emoji (one per line, within the four-box readback cap) with a non-grayscale foreground so the readback reports each cell. - New test
golden_emoji_sheet.rsruns the sheet, parses oneavg=(r,g,b,a)per glyph from the readback diagnostics, and compares against the golden (or regenerates it under the update flag). - New
sheet.jsoncommitting the reference averages for the four glyphs.
| File | Description |
|---|---|
crates/neomacs-gui-tests/tests/golden_emoji_sheet.rs |
Drives the GUI run, collects per-glyph cell averages, and diffs them against the golden with a per-channel tolerance and regeneration path. |
crates/neomacs-gui-tests/fixtures/golden-emoji/init.el |
Emacs Lisp fixture that draws the four COLRv1 emoji at startup and schedules shutdown so the readback window is deterministic. |
crates/neomacs-gui-tests/fixtures/golden-emoji/sheet.json |
Committed golden of the four emoji cell averages used as the comparison baseline. |
I verified the readback diagnostic format (glyph_box='{}' ... avg=({:.1},...), capped at four boxes), the four-emoji fixture, Cargo auto-discovery (no autotests = false), the golden key ordering versus comparison (key-based, so order-independent), and that the parsing/comparison logic and font accessors are correct. The duplicated glyph_box_average helper and fontconfig setup match the established self-contained per-test convention in this crate, so they are not flagged. I found no concrete defects.
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Follow-up to #544. The existing
colrv1_emojiGUI test proves cells are painted (hue assertions). It cannot see how they are painted: the two real regressions found after #544 — aPaintGlyphclip applied to its own fill, and a paint transform dropped — barely move a hue but visibly move edge coverage.Cell averages are the readback's own per-glyph statistic and are stable across renderers, unlike pixel-exact images, so this adds a golden of those averages:
fixtures/golden-emoji/init.eldraws four COLRv1 emoji, one per line (the readback diagnostics report at most four boxes —surface_readback.rscaps at four).tests/golden_emoji_sheet.rsruns the sheet, collects oneavg=(r,g,b,a)per glyph, and compares againstfixtures/golden-emoji/sheet.jsonwith a three-level per-channel tolerance.NEOMACS_GOLDEN_UPDATE=1regenerates the golden.Verified: comparison green; a ten-level perturbation of one channel fails with the exact delta (
1f347 channel 0: golden 218.60, measured 208.60) and a regeneration hint; regenerating restores green.