greetd-moongreet/DECISIONS.md
nevaforget 09371b5fd2 fix+perf: audit fixes and GPU blur migration (v0.5.0)
Address all findings from quality, performance, and security audits:
- Filter greetd error descriptions consistently (security)
- Re-enable power buttons after failed action (UX bug)
- Narrow TOCTOU window in avatar loading via symlink_metadata (security)
- Allow @ in usernames for LDAP compatibility
- Eliminate unnecessary Vec allocation in passwd parsing
- Remove dead i18n field, annotate retained-for-future struct fields
- Fix if/if→if/else and noisy test output in power.rs

Replace CPU blur (image crate + disk cache + async orchestration) with
GPU blur via GskBlurNode — symmetric with moonlock and moonset.
Removes ~15 transitive dependencies and ~200 lines of caching code.
2026-03-28 22:34:12 +01:00

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# Decisions
## 2026-03-28 GPU blur via GskBlurNode replaces CPU blur
- **Who**: Ragnar, Dom
- **Why**: CPU-side Gaussian blur (`image` crate) blocked the GTK main thread for 500ms2s on 4K wallpapers at cold cache. Disk cache and async orchestration added significant complexity.
- **Tradeoffs**: GPU blur quality is slightly different (box-blur approximation vs true Gaussian), acceptable for wallpaper backgrounds. Removes `image` crate dependency entirely (~15 transitive crates eliminated). No disk cache needed.
- **How**: `Snapshot::push_blur()` + `GskRenderer::render_texture()` on `connect_realize`. Blur happens once on the GPU when the widget gets its renderer, producing a concrete `gdk::Texture`. Zero startup latency. Symmetric with moonlock and moonset.
## 2026-03-28 Optional background blur via `image` crate (superseded)
- **Who**: Selene, Dom
- **Why**: Blurred wallpaper as greeter background is a common UX pattern for login screens
- **Tradeoffs**: Adds `image` crate dependency (~15 transitive crates); CPU-side Gaussian blur at load time adds startup latency proportional to image size and sigma. Acceptable because blur runs once and the texture is shared across monitors.
- **How**: `load_background_texture(bg_path, blur_radius)` loads texture, optionally applies `imageops::blur()`, returns blurred `gdk::Texture`. Config option `background-blur: Option<f32>` in `[appearance]` TOML section.
## 2026-03-28 Audit fixes for shared wallpaper texture (v0.4.1)
- **Who**: Selene, Dominik
- **Why**: Quality, performance, and security audits flagged issues in `load_background_texture()`, debug logging, and greetd error handling
- **Tradeoffs**: GResource path now requires UTF-8 (returns `None` for non-UTF-8 instead of aborting); 50 MB wallpaper limit is generous but prevents OOM; debug logging off by default trades observability for security
- **How**: GResource branch via `resources_lookup_data()` + `from_bytes()` (no abort), file size limit, error details only at debug level, `MOONGREET_DEBUG` env var for log level, greetd retry path truncation matching `show_greetd_error()`