Function _onWheel

modules/core/src/controllers/controller.ts:539–579

(event: MjolnirWheelEvent)

  // Default handler for the `wheel` event.
  protected _onWheel(event: MjolnirWheelEvent): boolean {
    if (!this.scrollZoom) {
      return false;
    }

    const pos = this.getCenter(event);
    if (!this.isPointInBounds(pos, event)) {
      return false;
    }
    event.srcEvent.preventDefault();

    const {speed = 0.01, smooth = false} = this.scrollZoom === true ? {} : this.scrollZoom;
    const {delta} = event;

    // Map wheel delta to relative scale
    let scale = 2 / (1 + Math.exp(-Math.abs(delta * speed)));
    if (delta < 0 && scale !== 0) {
      scale = 1 / scale;
    }

    const transitionProps = smooth
      ? {...this._getTransitionProps({around: pos}), transitionDuration: 250}
      : NO_TRANSITION_PROPS;

    const newControllerState = this.controllerState.zoom({pos, scale});
    this.updateViewport(
      newControllerState,
      transitionProps,
      {
        isZooming: true,
        isPanning: true
      }
    );

    // When there's no transition (duration = 0), immediately reset interaction state
    // since _onTransitionEnd callback won't fire
    if (!smooth) {
      this._setInteractionState({isZooming: false, isPanning: false});
    }
    return true;
  }

  protected _onMultiPanStart(event: MjolnirGestureEvent): boolean {
    const pos = this.getCenter(event);