galaxy-game/ui/docs/battle-viewer-ux.md

Battle Viewer UX

Phase 27 ships a dedicated viewer for battles (/games/<id>/battle/<battleId>). Bombings stay where they were in Phase 23 — a static table in the Reports view (section-bombings.svelte). The two domains are deliberately not mixed in any visual surface or click target.

Data shape

The BattleViewer component (lib/battle-player/battle-viewer.svelte) is logically isolated. It accepts a BattleReport matching pkg/model/report/battle.go. The fields it uses:

• id, planet, planetName — header + the central-planet glyph.
• races: { [raceId]: raceUUID } — race index space used by the protocol's a / d fields.
• ships: { [groupKey]: BattleReportGroup } — ship-group rosters with race name, className, initial num, end-state numLeft, and the inBattle flag. Observer groups (inBattle: false) are never drawn.
• protocol: BattleActionReport[] — flat list of shots. Each carries attacker (a, sa), defender (d, sd), and x (destroyed?).

The component asks timeline.ts.buildFrames(report) to expand the protocol into protocol.length + 1 frames; frame 0 is the initial state and frame N reflects state after action protocol[N-1]. The race index per ship group is derived from the protocol itself — every in-battle group appears at least once as attacker or defender, and the engine never crosses these wires.

Radial scene

The scene (lib/battle-player/battle-scene.svelte, SVG) places the planet at the centre and arrays the still-active races on an outer ring at equal angular spacing. Each race anchor hosts a cloud of class circles arranged on a Vogel sunflower spiral biased toward the planet (the cluster anchor is pushed inward by a quarter step so the rank-0 node — the heaviest group by NumberLeft — sits closest to the planet, and the spiral fans the rest behind it). When a race is wiped out, it drops out of the active list and the survivors are re-spaced on the next frame.

Each class circle is one bucket keyed by (race, className): tech-variants of the same class collapse into one node so the scene stays readable when a race fields a dozen tech levels of the same hull. The per-bucket label <className>:<numLeft> sums NumberLeft across the underlying groups; per-tech detail is available in the Reports view (Foreign Ship Classes / My Ship Types).

Circle radius scales with per-ship FullMass (Empty + Carrying via the per-ship LoadQuantity). The viewer resolves a (race, className) → ShipClassRef lookup from the surrounding GameReport.localShipClass + otherShipClass tables and runs it through the existing wasm bridge to pkg/calc/ship.go (emptyMass + carryingMass + fullMass). The radius is then MIN_RADIUS + (MAX_RADIUS − MIN_RADIUS) × sqrt(mass / maxMassInBattle) clamped to [6, 24] pixels — per-battle normalisation, so the heaviest ship in any given battle renders at the cap. Unknown class or invalid params fall back to MAX_RADIUS so the bucket stays visible.

The current frame's shot is drawn as a thin line from the attacker's class circle to the defender's class circle. Colour:

• red (#ee3344) when the action's x === true (the defender ship was destroyed),
• green (#44dd66) otherwise.

Each frame redraws the line in isolation, so continuous playback produces the "shot-shot-shot" pulse the user wanted.

Playback controls

lib/battle-player/playback-controls.svelte ships the full set:

Control	Effect
⏮ rewind	Stop, jump to frame 0
◀︎ step back	Stop, frame ← frame − 1
▶︎ / ⏸ play	Toggle continuous playback
▶︎▶︎ step fwd	Stop, frame ← frame + 1
1x / 2x / 4x	Speed switch: 400 / 200 / 100 ms per frame

When the timeline is at its end and the user hits play, the frame counter wraps to 0 and continues. Step buttons disable themselves at their boundary.

Accessibility

Below the scene the viewer renders a static <ol> text protocol — one line per action, formatted from BattleReportGroup.race and BattleReportGroup.className. The line for the current frame is highlighted so a non-visual reader can follow along by scrolling the log instead of watching the SVG. The list is always present and never hidden, satisfying the original Phase 27 acceptance "the same data is accessible as a static text log".

Height fit

The viewer is pinned to the viewport: .active-view uses calc(100dvh − 80px) so the in-game-shell header + optional HistoryBanner do not push the scene below the fold. Inside the viewer, the scene grows (flex: 1) and the log shrinks to a 30 dvh ceiling with its own internal scroll, so the page itself never scrolls vertically. The 80 px allowance maps to the current Header + HistoryBanner total on desktop; mobile breakpoints reuse the same calc because dvh tracks the dynamic viewport.

Map markers

map/battle-markers.ts emits two marker kinds per current-turn report. Both are wired into the binding's hitLookup so a click goes through the existing hit-test plumbing.

Battle marker — yellow cross

For every report.battles[i] whose planet resolves to a visible planet, the marker emits two LinePrim lines through the opposite corners of the square circumscribed around the planet circle. The result is an X-shaped cross overlaid on the planet glyph.

The stroke width is computed by battleMarkerStrokeWidth(shots): 1 shot → 1 px, 100 shots → 5 px, linearly interpolated in between (width = 1 + (shots − 1) × 4 / 99, clamped). A click on either line navigates to /games/<id>/battle/<battleId>?turn=<turn>.

Bombing marker — colored ring

For every report.bombings[i], the marker emits a single stroke-only CirclePrim slightly larger than the planet circle. Colour:

• yellow (#FFD400) when wiped: false,
• red (#FF3030) when wiped: true.

A click on the ring navigates to /games/<id>/report#report-bombings and scrolls the matching report-bombing-row (by data-planet) into view. Bombing markers never open the Battle Viewer — the two domains stay separate.

Data source

The Battle Viewer page (lib/active-view/battle.svelte) calls api/battle-fetch.ts.fetchBattle(gameId, turn, battleId). The loader has two modes:

• Synthetic — when gameId carries the synthetic- prefix, the lookup is served from api/synthetic-battle.ts. Vitest unit tests and Playwright e2e tests register fixture battles via registerSyntheticBattle before mounting the route.
• Production — otherwise the loader issues GET /api/v1/user/games/{gameId}/battles/{turn}/{battleId} against the backend gateway route added in backend/internal/server/handlers_user_games.go.Battle. The gateway forwards verbatim to the engine's GET /api/v1/battle/:turn/:uuid.

TODOs

• Push event game.battle.new + toast → viewer link (deferred — needs an engine emit-side change).
• Richer ship-class visuals derived from the class's mass, armament, shields. Current MVP uses a small circle plus <class>:<numLeft> label.
• Animated transitions when a race drops out and the survivors re-distribute. Current implementation hard-jumps on the next frame.