LibWeb: Resolve transform-origin against the transform reference box

[tcl3]

transform-origin is a resolved value special case property like height. The used value reported by getComputedStyle() resolves each offset against the transform reference box, with the Z offset left out when it is zero. Without a box the resolved value stays the computed value.

Previously, this was causing 4 / 1000 Domato test cases to crash when run with all style verification flags enabled.

Fixes #11154

[coderabbitai]

📝 Walkthrough

Walkthrough

The change adds computed-value handling for transform-origin. Positional keywords become percentages during style computation. Rendered elements resolve percentage and length values against a paintable reference box. Unrendered and display: contents elements preserve unresolved values. Zero Z offsets are omitted during serialization. Tests cover computed styles, SVG reference boxes, animation, interpolation, inheritance, calc(), shadow roots, and transitions.

Sequence Diagram(s)

sequenceDiagram
  participant CSSStyleProperties
  participant StyleComputer
  participant RustCSSComputation
  participant Paintable
  CSSStyleProperties->>StyleComputer: compute transform-origin
  StyleComputer->>RustCSSComputation: invoke computation rule
  RustCSSComputation-->>StyleComputer: return computed style value
  CSSStyleProperties->>Paintable: obtain reference box when rendered
  Paintable-->>CSSStyleProperties: return transform reference box
  CSSStyleProperties-->>CSSStyleProperties: serialize resolved offsets

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Possibly related PRs

• LadybirdBrowser/ladybird#10712: Introduces the ComputedValues migration used by the modified CSSStyleProperties and StyleComputer paths.
• LadybirdBrowser/ladybird#10869: Modifies Rust CSS length absolutization and viewport-dependency tracking used by transform-origin.

Merge Risk: 🟡 Moderate · up to 11baa

The change updates transform-origin resolution, but the interpolation expectations still describe percentages rather than the required resolved pixel lengths and zero-Z omission, which can leave the style tests failing or validating the wrong behavior. Merge should wait until those expectations are corrected.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The pull request adds broad WPT coverage and expected results for unrelated properties and transition behavior beyond transform-origin serialization.	Separate unrelated inheritance, transition, perspective-origin, and general transform test additions into a focused pull request.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description directly addresses transform-origin resolved-value serialization, missing reference boxes, and the related crashes.
Linked Issues check	✅ Passed	The changes resolve transform-origin against reference boxes, serialize HTML defaults as pixel lengths, and preserve computed values without a box for issue [#11154].

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In
`@Tests/LibWeb/Text/expected/wpt-import/css/css-transforms/animation/transform-origin-interpolation.txt`:
- Around line 150-173: Update all four transform-origin expectation blocks in
the fixture from percentages to resolved pixel lengths using the 50px by 50px
reference box; preserve the existing interpolated Z values, and omit the zero Z
component at progress 1. Apply the conversion consistently to the CSS
Transitions, transition-all, CSS Animations, and Web Animations cases.

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Fix all unresolved CodeRabbit comments on this PR:

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

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Run ID: 4cc96f2f-911d-4937-b141-083f712159ef

📥 Commits

Reviewing files that changed from the base of the PR and between 9e3d9c6 and 11baa4d.

📒 Files selected for processing (27)

• Libraries/LibWeb/CSS/CSSStyleProperties.cpp
• Libraries/LibWeb/CSS/Properties.json
• Libraries/LibWeb/CSS/StyleComputer.cpp
• Libraries/LibWeb/CSS/StyleComputer.h
• Libraries/LibWeb/Rust/src/css/style_compute.rs
• Libraries/LibWeb/Rust/src/css/table_group_builder.rs
• Tests/LibWeb/Text/expected/css/CSSStyleProperties-all-supported-properties-and-default-values.txt
• Tests/LibWeb/Text/expected/css/calc-coverage.txt
• Tests/LibWeb/Text/expected/css/getComputedStyle-print-all.txt
• Tests/LibWeb/Text/expected/css/transform-origin-computed-value-without-a-box.txt
• Tests/LibWeb/Text/expected/wpt-import/css/css-transforms/animation/transform-origin-composition.txt
• Tests/LibWeb/Text/expected/wpt-import/css/css-transforms/animation/transform-origin-interpolation.txt
• Tests/LibWeb/Text/expected/wpt-import/css/css-transforms/inheritance.txt
• Tests/LibWeb/Text/expected/wpt-import/css/css-transforms/parsing/transform-origin-computed.txt
• Tests/LibWeb/Text/expected/wpt-import/css/css-transforms/transform-origin-014.txt
• Tests/LibWeb/Text/expected/wpt-import/css/css-transforms/transform-origin-in-shadow.txt
• Tests/LibWeb/Text/expected/wpt-import/css/css-transforms/transforms-support-calc.txt
• Tests/LibWeb/Text/expected/wpt-import/css/css-transitions/properties-value-003.txt
• Tests/LibWeb/Text/input/css/transform-origin-computed-value-without-a-box.html
• Tests/LibWeb/Text/input/wpt-import/css/css-transforms/animation/transform-origin-composition.html
• Tests/LibWeb/Text/input/wpt-import/css/css-transforms/animation/transform-origin-interpolation.html
• Tests/LibWeb/Text/input/wpt-import/css/css-transforms/inheritance.html
• Tests/LibWeb/Text/input/wpt-import/css/css-transforms/parsing/transform-origin-computed.html
• Tests/LibWeb/Text/input/wpt-import/css/css-transforms/transform-origin-014.html
• Tests/LibWeb/Text/input/wpt-import/css/css-transforms/transform-origin-in-shadow.html
• Tests/LibWeb/Text/input/wpt-import/css/css-transforms/transforms-support-calc.html
• Tests/LibWeb/Text/input/wpt-import/css/css-transitions/properties-value-003.html

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