# Battle Viewer UX Phase 27 ships a dedicated viewer for battles (`/games//battle/`). 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 `:` 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 `
    ` 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//battle/?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//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 `:` label. - Animated transitions when a race drops out and the survivors re-distribute. Current implementation hard-jumps on the next frame.