skills/docs/media/audio/audio-timeline/src/engine/zoom/zoom.md

Engine Zoom Helpers

(no submodules)

Purpose

The zoom.ts module bridges TimelineEngine zoom, selection, and loop public methods to the pure timeline-operations.ts and zoom.ts helpers. It manages internal state updates and event emission so the engine class stays focused on high-level orchestration.

Features

• engineZoomIn / engineZoomOut step through the zoom table and emit zoomChange
• engineSetZoomLevel snaps to the nearest table entry
• engineSetSelection normalises ranges and emits selectionChange
• engineSetLoopRegion updates loop bounds and forwards to adapter
• engineSetLoopEnabled toggles loop and forwards to adapter

Usage

These helpers are used internally by TimelineEngine. Consumers call engine.zoomIn() etc.

API Reference

Export	Signature	Description
engineZoomIn	(deps) => void	Zoom in
engineZoomOut	(deps) => void	Zoom out
engineSetZoomLevel	(deps, samplesPerPixel) => void	Set zoom
engineSetSelection	(deps, start, end) => void	Set selection
engineSetLoopRegion	(deps, start, end) => void	Set loop region
engineSetLoopEnabled	(deps, enabled) => void	Toggle loop

Implementation Notes

The ZoomDeps interface isolates the helpers from the engine class, making them testable in isolation. Loop changes are forwarded to the adapter immediately so the audio backend can update its loop markers. Selection changes are clamped to the current document duration so invalid ranges cannot be created. Zoom changes only affect the view and do not touch the arrangement, which is why they bypass the undo stack entirely.