Chapter 07b

Scene transitions

When the sign changes base scene (for example boot → idle clock, or idle clock ↔ launch countdown), B0rd OS blends the outgoing frame into the incoming one using a curated transition. Names are stable string ids shared by settings docs, Host CLI, and automation.

Catalog

Id	Behavior
`cut`	Instant swap. No intermediate frames.
`fade`	Crossfade (pixel blend). Default for boot → idle clock and most base changes.
`slide_left`	New scene enters from the right and covers the old (outgoing stays put).
`slide_right`	Mirror of slide left — enters from the left.
`slide_up`	New scene enters from the bottom and covers upward.
`slide_down`	New scene enters from the top and covers downward.
`push_left`	New scene enters from the right and pushes the old off to the left (both move).
`push_right` / `push_up` / `push_down`	Same displace semantics on the other axes.

Slide vs push

Slide is a cover: the outgoing scene stays fixed until the incoming frame paints over it. Push displaces both frames so the outgoing content leaves the viewport as the incoming content arrives. On a small matrix the difference is easy to see when the outgoing frame has spatial detail (clock hands, countdown chrome).

Timing and accessibility

Duration defaults to scene.timing.crossfade_ms (USB / settings; default 1,000 ms). Set to 0 for an instant cut-equivalent.
scene.timing.enter_transition selects the catalog id for every base playlist A→B handoff (auto = each scene plugin's claim). Duration still comes from scene.timing.crossfade_ms.
a11y.reduce_motion forces a non-animated path (instant swap) for every catalog entry — no slide, push, or fade progress.

Defaults today

Boot → the current base presentation uses fade when reduce-motion is off andcrossfade_ms > 0. Idle clock ↔ launch countdown also default to fade via each scene plugin'senter_transition claim unless the operator setsscene.timing.enter_transition to a catalog id (auto restores per-scene defaults). Notification cues usescene.notification.enter_transition /scene.notification.exit_transition — separate from base playlist wipes.