Snapping

While you draw or move something, the editor looks for a snap target near the pointer and shows it as a marker before you click. The point then lands exactly on the target, so new geometry connects to existing geometry instead of ending next to it.

What a point snaps to#

Within the snap radius, in this order of preference:

1. a corner (an existing node),
2. the middle of an edge,
3. a quarter point of an edge (one quarter or three quarters along),
4. anywhere on an edge (the foot of the perpendicular).

A closer target of a lower kind does not beat a corner: the order decides first, distance only within one kind. Only the active layer's own geometry is searched this way — a click can still land on another layer's boundary, but never by accident: only via an active Geofencing rule naming that layer as its target (vectorstream Pro), or via editor.nachzeichnenVorlagen naming it as a tracing template (below). Either way, the point itself stays free-standing on the active layer's own partition; nothing ties it to the layer it was found on.

Each of the four kinds can be switched off on its own: editor.rastArten (default all four, in the order above) — the same division as rastenAktiv, for every tool that asks through ctx.rasten(...). A mode that restricts the kinds itself on a particular call keeps exactly that restriction; this setting only fills in the default where a mode leaves the choice open. An empty array means no snapping at all, same as rastenAktiv = false, just reversible one kind at a time.

Does not reach transform (drag, rotate, scale). That mode snaps a moved corner onto a foreign corner, division point, or edge on its own, by calling the core's rastziel directly — never through ctx.rasten(...) — so rastArten has no effect there; dragging always offers all four kinds. rastenAktiv has no such gap: it works through the shared snap tolerance, which transform also reads, so switching snapping off entirely still reaches it — only the four-way split does not.

Not retroactive. Switching a kind off does not by itself erase an already-shown marker of that kind: the active mode's last snap target is only recomputed on the next pointer move, like every other ctx.rasten(...)-driven display.

The radius is given in screen pixels — new Editor(…, adapter, { tolerancePx }), default 8 — and the adapter converts it to map units for the current zoom, so snapping feels the same at every zoom level. editor.tolerancePixel() returns the value, for a UI that wants to use the same one.

Guide lines#

While drawing, imagined lines help to align a point:

• horizontal and vertical axes through the points already placed — those through the first and the last placed point are shown the whole time;
• the extension of existing edges;
• the right angle to the edge drawn last;
• the intersection of two guide lines, which counts like a corner.

A guide line pulls the point onto it but lets it slide along it. Guide lines are switched with editor.hilfslinienAktiv (default on).

Tracing along existing boundaries#

If two consecutive clicks both snap onto existing boundaries, the polygon and line tools insert the path along those boundaries between them, vertex by vertex, instead of a straight segment (where no such path is found, the segment stays straight). When a polygon is closed, the closing segment back to the first point is traced the same way. The preview shows the traced path before you click. Backspace removes a traced section as a whole. Switched with editor.nachzeichnenAktiv (default on). For cut and difference, tracing only happens while Shift is held.

editor.nachzeichnenVorlagen extends this across layers: a ReadonlyMap<EbenenId, readonly EbenenId[]> from a layer to the layer(s) it may additionally trace along, keyed by the layer doing the tracing. A click that snaps onto a named template layer's own boundary traces the whole path there too — the vertices in between are inserted as free points on the active layer, each rounded onto its own grid. This is independent of Geofencing (above): no rule, no validation, no undo entry of its own, and it creates no topology between the two layers — the traced points are exactly as free-standing as a hand-placed point at the same spot. Not persisted: an application that wants it to survive a reload sets it again after loading a document, the same as rastenAktiv. A layer absent from the map, or one named but since removed, is silently passed over — exactly as if nothing had been named.

Switching snapping off#

• Alt suspends snapping while it is held: the click lands exactly where the pointer is. This also stops the insert operation from merging the point with a nearby node.
• editor.rastenAktiv = false switches snapping off until it is switched on again (default on).

import type { Adapter } from '@vectorstream/adapter';
import type { Partition } from '@vectorstream/core';
import { Editor } from '@vectorstream/editor';

export function createEditorWithSnapping(partition: Partition, adapter: Adapter): Editor {
  // Snap radius in screen pixels (default 8); the adapter converts it for the current zoom.
  const editor = new Editor(partition, adapter, { tolerancePx: 12 });

  editor.rastenAktiv = true; // snapping at all (default on; Alt suspends it while held)
  editor.hilfslinienAktiv = false; // no guide lines (alignment, extensions, right angle)
  editor.nachzeichnenAktiv = true; // trace along existing boundaries between two snapped clicks
  editor.rastArten = ['ecke', 'kante']; // only corners and edges — no midpoints or quarter points
  return editor;
}

The test of this example clicks 9 by 5 pixels beside a parcel corner: with the radius of 12 pixels the new vertex lands on the corner; with rastenAktiv = false, or with Alt held, it does not.

What does not snap#

• Lines are inserted exactly: the line tool snaps each click as described above, but the insert itself uses no tolerance. Calling insertLine with a tolerance above zero throws a RangeError.
• A click still never snaps to another layer by default — only the target layers of an active Geofencing rule (vectorstream Pro; most kinds of rule, after the layer's own geometry) or an explicitly named nachzeichnenVorlagen template layer can be reached, and even then only as a snap target, never as real topology (see Layers).
• Validation does not use the snap radius: it always checks with tolerance zero (see Validity and rejections).

API: Editor, EditorOptions.