Category filter in Timeline view

[McTom234]

I think it would be nice to be able to filter for categories in timelines. This would sometimes drastically reduce the amount of events shown and therefore improve the performance a lot.

PS: Awesome work on this project. Coming from WakaTime, I am so happy to have found an OSS alternative! Donation is already setup ❤️ keep up the good work!

[TimeToBuildBob]

Good feature request. The Timeline currently shows raw bucket events with no category filtering, which means hundreds of tiny event rectangles for a busy day.

Implementation approach:

The category system already runs queries for the Activity view — the same canonicalEvents() pipeline can be reused. A category filter would:

1. Add a dropdown/multi-select above the timeline (populated from the user's categorization rules)
2. Run the categorization query on the visible time range
3. Filter timeline events to only show those matching selected categories
4. Optionally: add a "Categories" row showing merged category blocks (related: Daily timeline should contain a row for final categories #700)

The AFK filter toggle in PR #776 establishes the pattern for this — it adds a toggle that runs events through canonicalEvents() before rendering. A category filter would extend that same mechanism with an additional filter step.

Performance benefit: As you noted, filtering to 1-2 categories would dramatically reduce DOM elements. The Timeline's main performance bottleneck (#516) is rendering hundreds of SVG rectangles — filtering at the data level before rendering would be a significant win.

This would pair naturally with the Vue 3 migration (#772) since the component architecture will be cleaner. Would be a good follow-up once Phase 2 of the migration lands.

[TimeToBuildBob]

Implemented in PR #778 — adds a category filter dropdown to the Timeline view.