feat: improve splitview horizontal image pairing

[Zaida-3dO]

Problem: The original splitview logic only paired horizontal images if they were adjacent (positions 0 and 1). If a vertical image was between two horizontal ones, the first horizontal would display alone, looking awkward.

Summary

• Smarter horizontal image pairing in splitview layout - looks ahead at 3 candidates instead of 2
• Skips vertical images to pair horizontal images that aren't adjacent in the queue
• Avoids showing lone horizontal images that look awkward in splitview

Drive by fix

• Passes clientIdentifier on asset requests to improve logs
• The original isHorizontal() function actually checked if height > width (portrait orientation). Renamed to isPortrait() for clarity.

Details

Solution: New selectAssetsForDisplay() function with smarter logic:

• If first image is vertical → show it alone
• If first and second are both horizontal → pair them [0, 1]
• If first is horizontal, second is vertical, third is horizontal → pair [0, 2], skipping the vertical
• If first is horizontal with no horizontal partner → skip it and show the vertical instead

This improves the visual experience by maximizing horizontal pairings and avoiding lone horizontal images in splitview.

Open question/discussion

I was thinking about making this configurable for back compat reasons, by adding a "splitview-forced" option for layout, but that felt like overkill and I struggle to think of a valid use case for wanting to keep the "sometimes splitview shows a lone portrait item" behaviour. So opted to just change the default behavior for all "splitview"

Summary by CodeRabbit

Summary by CodeRabbit

• Refactor
  • Improved asset selection and navigation when browsing your photo library, with smarter candidate-based selection and better handling of portrait/landscape orientations (improves pairing and layout display).
  • Asset requests now consistently include client identifier for image loading.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Home page asset loading now includes a clientIdentifier and replaces backlog/history batching with candidate-based selection and orientation-aware display logic via new helpers that pick and remove asset indices and update portrait detection.

Changes

Cohort / File(s)

Summary

Asset Selection Refactor immichFrame.Web/src/lib/components/home-page/home-page.svelte

Asset requests now pass clientIdentifier. Removed previous backlog/history batching logic and introduced candidate-based selection: getNextAssets takes up to 3 candidates from the front of assetBacklog, getPreviousAssets takes up to 3 from the end of assetHistory (reversed for selection). Added selectAssetsForDisplay(layout, candidates) to choose which candidate indices to display (prioritizes portrait pairings in splitview), and removeAtIndices(arr, indicesToRemove) to remove elements by index. Renamed isHorizontal → isPortrait and updated orientation logic to handle flipped dimensions. Comments and flow updated accordingly.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 I nibble through the asset stack with glee,
Picking three candidates for screens to see,
Portraits pair where splitviews play,
Indices hop off, then fade away,
The homepage shuffles — neat as can be!

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title clearly and concisely summarizes the main change: improving splitview horizontal image pairing logic.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@immichFrame.Web/src/lib/components/home-page/home-page.svelte`:
- Around line 217-251: The pairing logic is inverted because isHorizontal()
currently returns imageHeight > imageWidth (true for portrait), causing
selectAssetsForDisplay() (variables h0, h1, h2 and checks like if (!h0), if
(h1), etc.) to treat portrait images as "horizontal"; fix by changing
isHorizontal() to return imageWidth > imageHeight so its boolean matches its
name and the intended pairing logic, then run/adjust any comments or tests
referencing isHorizontal() behavior to reflect the corrected orientation
semantics.