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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 500ms–2s 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2026-03-28 – Optional background blur via image crate (superseded)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()