fix(pptx): center resized slide content in pixel coordinates

[yunfeizhu]

What does this change?

Fixes #85.

Convert the shared slide-size centering offsets from EMU to pixels before applying them to element frames. Ensure Fit and Maximize now keep content correctly positioned in all five framework bindings, including after saving and reopening.

Type of change

• Bug fix (non-breaking)

Area

src/core/pptx/editor/render: one DOM-free fix shared by every binding.

Testing

• Regression tests fail on the original implementation; both resize modes pass a real PPTX save/reload check.
• bun run verify --base 260a953eabdd657fb744b8c4881d03f51da27a45: all 21 steps passed, including affected core/UI tests, builds, typechecks and viewer suites with React 18 compatibility.
• Browser regression: 10/10 passed, Ensure Fit and Maximize in React, Vue, Angular, Vanilla and Svelte, checking visible content and the downloaded PPTX.
• Previous fork CI passed for 9819b2661a322f42d9774f9602fb7d4bb0d71612 with scope=changed.

Screenshots / recordings

Reproduction PPTX

Summary by CodeRabbit

• Bug Fixes

  • Corrected slide-resizing offsets so content is centred at the expected position when fitting or maximising slides, including portrait layouts.

• Tests

  • Added coverage for resizing, saving and reloading presentations, checking slide dimensions, content positions and slide bounds.

[pkg-pr-new]

• ooxml-office-preview

  npm i https://pkg.pr.new/ooxml-core@87ffeda
  

  npm i https://pkg.pr.new/ooxml-ui@87ffeda
  

commit: 87ffeda

[coderabbitai]

Important

Review skipped

Review was skipped as selected files did not have any reviewable changes.

⛔ Files ignored due to path filters: 1

• src/core/pptx/__tests__/fixtures/slide-size-centering.pptx is excluded by !**/*.pptx, !**/fixtures/**

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📥 Commits

Reviewing files that changed from the base of the PR and between 4e0c49b and 87ffeda.

⛔ Files ignored due to path filters: 1

• src/core/pptx/__tests__/fixtures/slide-size-centering.pptx is excluded by !**/*.pptx, !**/fixtures/**

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• Configuration used: Repository: ChristopherVR/ooxml/.coderabbit.yaml
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• Run ID: 1068b58f-7139-4bbc-a8c5-9ef6bcad593e

📥 Commits

Reviewing files that changed from the base of the PR and between 260a953 and 9819b26.

⛔ Files ignored due to path filters: 2

• docs/bug-repros/pptx-slide-size-centering.png is excluded by !**/*.png
• src/core/pptx/__tests__/fixtures/slide-size-centering.pptx is excluded by !**/*.pptx, !**/fixtures/**

📒 Files selected for processing: 4

• e2e/pptx/slide-size-centering.spec.ts
• src/core/pptx/editor/render/slide-size-rescale.roundtrip.test.ts
• src/core/pptx/editor/render/slide-size-rescale.test.ts
• src/core/pptx/editor/render/slide-size-rescale.ts

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📝 Walkthrough

The slide-size transform now converts its centred offsets from EMU to pixels. Unit, round-trip, and end-to-end tests cover ensure-fit and maximize, including element positions after saving and reloading.

Priority: ➖ Normal

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 9819b

No actionable issue remains identified for this slide-centering change; it is mergeable after normal checks.

Security architecture risk: 🔵 Low · up to 9819b

The change corrects slide positioning without introducing a new security boundary or privileged operation. Compatibility risk is limited to callers that may have interpreted the exported helper’s previous offsets as EMU rather than pixels.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The changed computation affects slide-element geometry through an existing document-editing path. The inspected implementation performs numeric transformation and object copying, not credential access, network operations, or privileged execution.

Pre-merge checks: 5

Check name	Status	Explanation
Linked Issues check		Issue #85 requires the shared slide-size operation to keep content centred and visible for Ensure Fit and Maximize after a 4:3-to-widescreen change, including after save and reload, for all framework …
Out of Scope Changes check		The implementation changes only the shared slide-size rescale transform. The added unit, round-trip, and Playwright tests verify the linked issue behaviour. No unrelated product or API changes are ide…
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 1 functions across 4 files.
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the PPTX fix and the change from EMU to pixel coordinates. It matches the main purpose of the pull request.

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[ChristopherVR]

Thanks, this is a real bug and the fix is in the right place.

Element frames are in pixels but the centring offsets were in EMU, so Ensure Fit and Maximize pushed content far off the slide. Every binding goes through the shared scaleSlidesForSizeChange, so converting the offsets once in resolveSlideSizeRescaleTransform covers all five, and nothing else in the repository depended on EMU offsets. The tests are good: the portrait cases, the save-and-reload round trip on a real deck and the cross-binding browser spec.

Two small requests before merge:

• Please drop docs/bug-repros/pptx-slide-size-centering.png. It starts a new folder of PR screenshots in the repository; the image is better kept in the PR description.
• resolveSlideSizeRescaleTransform is exported (ooxml-core/pptx/editor, re-exported from ooxml-ui/pptx) and its offsets change from EMU to pixels. A line in the commit body saying so would help any outside caller.

[yunfeizhu]

Thanks for the review, @ChristopherVR! Updated in 4e0c49b: removed the PNG from the commit and moved it to GitHub attachments in the PR and issue descriptions. The commit body now explicitly documents that resolveSlideSizeRescaleTransform returns offsetX/offsetY in pixels instead of EMU.

The .pptx fixture remains because the round-trip and browser tests load it directly. The PR still contains one commit.