# `Input.startDrag`

> Contract 2.0.0 · package sha256 `a857eca95b35921109faf997094bb4192f12527d9d0fcd4be7e97f06425bad6e` · generated from `configurator-runtime.d.ts` by `services/onsite-scripter/scripts/build-contract-docs.mjs`; edit the source, not this file.

Method of [`Input`](Input.md) · labs, `@experimental` · since 2.0.0 · called as `session.input.startDrag` · optional: reach it through `has()`

```ts
startDrag?(part: Part, from: {
  pointerId: number;
  at: ScreenPoint;
}): void;
```

Starts a drag from a pointer that is already down (a long press). `at`: CSS px from your boot
`el`. The part's unit must be named by a live [`input.drag`](Input.drag.md) registration, and the newest that
names it applies, as for a press; registering is immediate, so register first (or again with
the part added). The runtime's camera input gives up `pointerId`: an orbit it started on that
pointer stops where it is. Experimental: reach it through [`has(session, 'input.startDrag')`](has.md).
Errors: throws HoloInputError 'not-draggable' when no live registration names the unit.

## Generic-API test (spec 3.1)

| Rule | Result |
| --- | --- |
| 1. Neutral name | pass: `startDrag` names no product |
| 2. A precedent | pass: [Babylon.js PointerDragBehavior (startDrag, onDragObservable, validateDrag)](https://github.com/BabylonJS/Babylon.js/blob/master/packages/dev/core/src/Behaviors/Meshes/pointerDragBehavior.ts) (row `G2`); [jQuery UI draggable (drag, revert)](https://api.jqueryui.com/draggable/) (row `K47`) |
| 3. Two apps, or labs | labs (`@experimental` at a stable path, reached through `has()` or `supports()`): it graduates when a second app uses it; apps today: app-04c2774145, app-37356bf09f, app-4762caacdc, app-fc07850558, app-fc306ec3dc |
| 4. The cheaper fix first | decided per need in Appendix B: rows `G2`, `K47` at tier labs, stable (a member only where no rule, data, asset or app code serves the need) |