LibGfx+LibWeb: Use per-code-point font fallback for SVG text

[sideshowbarker]

Problem: Characters a generic font doesn’t cover drew as missing-glyph boxes inside SVG text; e.g. U+1D11E with font-family:serif — while the same character renders correctly in ordinary HTML text, and naming a font that does cover it renders it correctly inside SVG as well.

Cause: The SVG text path builder resolved one font for a whole run with first_available_font() — the first font in the list that covers the space character — and then handed the entire string to Skia to map through that font alone. So any code point outside it became glyph 0.

Fix: Shape each run with Gfx::shape_text() against the box’s full font list — the same way HTML text and canvas text already did. Fixes #11031.

Note

This PR branch contains two commits: The first commit has the change described above, while the second commit is entirely just deletions of the Path::text() and place_text_along() code — which no longer has any callers, after the change to using Gfx::shape_text() against the box’s full font list.

So, it might be easier to first review the first commit in isolation, and then review the deletions.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 826a8ed3-e730-458b-9b85-2ad47772b972

📥 Commits

Reviewing files that changed from the base of the PR and between 7192c79 and e96c05e.

⛔ Files ignored due to path filters (3)

• Tests/LibWeb/Screenshot/expected/svg-gradient-paint-transformation.png is excluded by !**/*.png
• Tests/LibWeb/Screenshot/expected/svg-text-effects.png is excluded by !**/*.png
• Tests/LibWeb/Screenshot/expected/svg-textPath.png is excluded by !**/*.png

📒 Files selected for processing (11)

• Libraries/LibGfx/Path.h
• Libraries/LibGfx/PathSkia.cpp
• Libraries/LibGfx/PathSkia.h
• Libraries/LibWeb/Layout/LayoutRustBridge.cpp
• Tests/LibWeb/Layout/expected/css-namespace-tag-name-selector.txt
• Tests/LibWeb/Layout/expected/svg-text-dominant-baseline.txt
• Tests/LibWeb/Layout/expected/svg-text-with-percentage-values.txt
• Tests/LibWeb/Layout/expected/svg-text-with-viewbox.txt
• Tests/LibWeb/Layout/expected/svg/svg-text-positioning.txt
• Tests/LibWeb/Ref/expected/svg-text-font-fallback-ref.html
• Tests/LibWeb/Ref/input/svg-text-font-fallback.html

🚧 Files skipped from review as they are similar to previous changes (10)

• Tests/LibWeb/Layout/expected/css-namespace-tag-name-selector.txt
• Tests/LibWeb/Ref/input/svg-text-font-fallback.html
• Tests/LibWeb/Layout/expected/svg-text-with-viewbox.txt
• Libraries/LibGfx/PathSkia.h
• Tests/LibWeb/Ref/expected/svg-text-font-fallback-ref.html
• Tests/LibWeb/Layout/expected/svg-text-with-percentage-values.txt
• Libraries/LibWeb/Layout/LayoutRustBridge.cpp
• Tests/LibWeb/Layout/expected/svg/svg-text-positioning.txt
• Libraries/LibGfx/PathSkia.cpp
• Libraries/LibGfx/Path.h

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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📝 Walkthrough

Walkthrough

LibGfx replaces UTF-8 and UTF-16 text placement APIs with glyph-run placement APIs. The Skia backend transforms glyph outlines along paths using glyph positions, widths, and path tangents. SVG layout now shapes text with the complete font list for fallback support, uses glyph runs for measurement and rendering, and places them along paths. Layout expectations and SVG font-fallback tests were updated.

Sequence Diagram(s)

sequenceDiagram
  participant SVGLayout
  participant GfxShapeText
  participant PathSkia
  SVGLayout->>GfxShapeText: Shape text with the font list
  GfxShapeText-->>SVGLayout: Return glyph runs
  SVGLayout->>PathSkia: Place glyph runs along the path
  PathSkia-->>SVGLayout: Return transformed glyph outlines

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Suggested reviewers: kalenikaliaksandr

Merge Risk: ⚪ Minimal · up to e96c0

SVG text now selects fallback fonts per code point, preventing missing-glyph boxes for unsupported characters while preserving the existing rendering path. No actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description check	✅ Passed	The pull request description directly explains the SVG font-fallback defect, its cause, the glyph-run shaping fix, and the removal of unused path text APIs. These changes match the summarized changese…
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.

Full details: Description check

Explanation

The pull request description directly explains the SVG font-fallback defect, its cause, the glyph-run shaping fix, and the removal of unused path text APIs. These changes match the summarized changeset.

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