Function beforestart

external/.d3.js:2817–2862

(that, container, event, d, identifier, touch)

  }

  function beforestart(that, container, event, d, identifier, touch) {
    var dispatch = listeners.copy(),
        p = pointer(touch || event, container), dx, dy,
        s;

    if ((s = subject.call(that, new DragEvent("beforestart", {
        sourceEvent: event,
        target: drag,
        identifier,
        active,
        x: p[0],
        y: p[1],
        dx: 0,
        dy: 0,
        dispatch
      }), d)) == null) return;

    dx = s.x - p[0] || 0;
    dy = s.y - p[1] || 0;

    return function gesture(type, event, touch) {
      var p0 = p, n;
      switch (type) {
        case "start": gestures[identifier] = gesture, n = active++; break;
        case "end": delete gestures[identifier], --active; // falls through
        case "drag": p = pointer(touch || event, container), n = active; break;
      }
      dispatch.call(
        type,
        that,
        new DragEvent(type, {
          sourceEvent: event,
          subject: s,
          target: drag,
          identifier,
          active: n,
          x: p[0] + dx,
          y: p[1] + dy,
          dx: p[0] - p0[0],
          dy: p[1] - p0[1],
          dispatch
        }),
        d
      );
    };
  }

  drag.filter = function(_) {
    return arguments.length ? (filter = typeof _ === "function" ? _ : constant$9(!!_), drag) : filter;