Fix blank DMG background

[FuJacob]

Summary

• Removes the sips --resampleHeightWidth call in normalize_background_image
• The background asset (dmg_background.png) is already authored at 2x resolution (1080×1520 px for a 540×760 pt window) — downsampling it to 1x point size made it too small for Finder to apply as a background on Retina displays, causing a blank DMG window

Test plan

• Run bash scripts/build_test_dmg.sh
• Open the resulting /tmp/Tabby-test.dmg and verify the background image appears

🤖 Generated with Claude Code

Greptile Summary

This PR fixes the blank DMG background by replacing the previous single-PNG approach (where the 2x image was being downsampled to 1x point size by sips, making it too small for Finder on Retina displays) with a proper multi-rep TIFF generated via tiffutil -cathidpicheck — the canonical macOS approach Apple's own installers use.

• The asset split creates a true 1x PNG (dmg_background.png) and a dmg_background@2x.png, combined at build time into a multi-rep TIFF so Finder selects the right resolution per display.
• build_test_dmg.sh gains a PEP 668–safe isolated venv for Homebrew Python environments and CODE_SIGNING_ALLOWED=NO for local dev builds without a signing cert.
• The volume name is consistently renamed from tabby → Tabby across CI and the test script.

Confidence Score: 5/5

Safe to merge — the change is additive and well-scoped, touching only DMG packaging assets and scripts with no impact on the app binary or update pipeline.

The root-cause fix (blank background on Retina displays) is addressed correctly: tiffutil -cathidpicheck is the canonical macOS mechanism for multi-rep HiDPI backgrounds, the 1x/2x asset split is consistent across CI and the test script, and the CI workflow already has dmgbuild installed before the new tiffutil call runs. No logic errors or broken contracts were found in the changed paths.

No files require special attention. The open items (stale docstrings, version-pin mismatch) were flagged in previous review rounds and are style-level concerns that do not affect packaging correctness.

Important Files Changed

Filename	Overview
scripts/build_release_dmg.py	Replaces sips resampling with tiffutil -cathidpicheck to produce a multi-rep TIFF; adds --background-2x-path CLI arg; stale docstring references (sips, step 3 description) were flagged in previous review rounds and remain unaddressed.
scripts/build_test_dmg.sh	Adds PEP 668-safe venv, CODE_SIGNING_ALLOWED=NO for local builds, passes --background-2x-path; removes the duplicate eject loop; the
.github/workflows/release.yml	Adds --background-2x-path pointing to the new asset and renames the volume from tabby to Tabby; CI already installs dmgbuild==1.6.7 in the Install DMG packaging dependencies step, so the new tiffutil path will work without any dependency changes.
assets/release/dmg_background.png	Replaced with the proper 1x (540x760 pt) version; the former 2x content was moved to dmg_background@2x.png.
assets/release/dmg_background@2x.png	New file containing the original 1080x1520 px (2x) background art, now properly identified and used as the HiDPI resolution source for tiffutil.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["dmg_background.png (1x · 540×760)"] --> C[tiffutil -cathidpicheck]
    B["dmg_background@2x.png (2x · 1080×1520)"] --> C
    C --> D["dmg-background.tiff (multi-rep HiDPI)"]
    D --> E[dmgbuild settings.py]
    G["tabby.app (signed)"] --> H[ditto → staging-root]
    H --> E
    E --> F[dmgbuild]
    F --> I[Tabby.dmg]
    I --> J{Finder display}
    J -->|Retina| K[2x rep · crisp]
    J -->|Non-Retina| L[1x rep · correct size]

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Comments Outside Diff (3)

1. scripts/build_release_dmg.py, line 73-75 (link)

   The run_command docstring still lists sips as one of the "system-tool boundaries" it crosses, but sips is no longer called anywhere in the script after this change. The mention will mislead future readers who try to trace which external tools this script depends on.

   

2. scripts/build_release_dmg.py, line 106-107 (link)

   The install hint in ensure_dmgbuild_available still pins ==1.6.7, while build_test_dmg.sh now uses >=1.6.0. Anyone following the error message to install the package will end up with a different version than the test script installs, which could mask compatibility issues. The two should agree on a version constraint.

   

3. scripts/build_release_dmg.py, line 10 (link)

   The module-level docstring step 3 still says "Normalize the committed background art to the Finder window size we want", which described the old resampling behaviour. After this change the function only copies the file, so the description is slightly misleading.

   

_{Reviews (5): Last reviewed commit: "Update DMG background assets and build s..." | Re-trigger Greptile}