Camera
The camera is the viewport — the zoom and pan that map world coordinates onto the screen. Camera state lives in the scene's viewport but is editor-local: it is never recorded in undo history.
Click Detection
Click detection answers "what is under this point?" — the hit-test that turns a world-space coordinate into the thing the user pressed: an element, a resize handle, a link, a link endpoint, an annotation pin, or empty canvas.
Clipboard
Copy, cut, and paste move the current selection through an in-editor buffer. The engine exposes them as verbs; the corresponding actions (actionCopy, actionCut, actionPaste) wire them to standard hotkeys.
Drag And Drop
Dropping a file onto the canvas is dispatched through a host-extensible registry. Built-in handlers cover images and videos; hosts add their own for custom payloads (CSV, scene JSON, …).
Edge Scrolling
Edge scrolling would automatically pan the viewport when a drag (moving a shape, drawing a selection box) reaches the edge of the canvas, so you can drag content beyond what is currently visible.
Eraser
The eraser is the erase mode (hotkey E, actionModeErase). Press-and-drag sweeps shapes under the cursor into a pending set — previewed dimmed — and releasing deletes them all in one undo step, dropping their attached links exactly like a Delete-key delete. A plain click erases the shape under it.
Focus
Focus handling keeps canvas keyboard shortcuts from stealing keystrokes meant for a text field. Whenever the user is typing into an `, , , or any contenteditable` host, global handlers must stand down.
Handles
Handles are the eight resize grips (plus rotation anchor) drawn around a
Highlighting
There is no general-purpose "highlight this shape" API (a setter that paints an arbitrary accent ring around any element on demand). What the editor does have is a set of contextual hover highlights, drawn by the overlay during specific interactions:
History
Undo / redo is backed by @oh-just-another/history — a transactional, invertible patch stack. The engine drives it for you; you can also use the kernel directly for headless replay or server-side audit.
Indicators
Selection indicators are the on-canvas chrome that surrounds the current
Input Handling
The engine never touches the DOM directly. Hosts translate raw browser events into normalized, CSS-pixel domain events and feed them in. This keeps the core framework-agnostic and testable, and lets non-browser hosts drive the same engine.
Pen Mode
Freehand drawing is available through the editor's brush mode, which produces pressure-sensitive strokes (BrushElement). It is the pen-like tool today.
Readonly
Read-only (view) mode is a single engine-level flag that gates all editing while leaving pan, zoom, and selection alive. Toggle it with ⌥R (actionToggleReadOnly) or programmatically:
Selection
Selection is the set of elements the user is currently acting on. The engine owns it as immutable state and exposes verbs to read and mutate it; links (connectors) are first-class members of the selection and coexist with selected elements.