Method _getPointerPositionInElement

src/cdk/drag-drop/drag-ref.ts:1250–1266

* Figures out the coordinates at which an element was picked up. * @param referenceElement Element that initiated the dragging. * @param event Event that initiated the dragging.

(
    elementRect: DOMRect,
    referenceElement: HTMLElement,
    event: MouseEvent | TouchEvent,
  )

   * @param event Event that initiated the dragging.
   */
  private _getPointerPositionInElement(
    elementRect: DOMRect,
    referenceElement: HTMLElement,
    event: MouseEvent | TouchEvent,
  ): Point {
    const handleElement = referenceElement === this._rootElement ? null : referenceElement;
    const referenceRect = handleElement ? handleElement.getBoundingClientRect() : elementRect;
    const point = isTouchEvent(event) ? event.targetTouches[0] : event;
    const scrollPosition = this._getViewportScrollPosition();
    const x = point.pageX - referenceRect.left - scrollPosition.left;
    const y = point.pageY - referenceRect.top - scrollPosition.top;

    return {
      x: referenceRect.left - elementRect.left + x,
      y: referenceRect.top - elementRect.top + y,
    };
  }

  /** Determines the point of the page that was touched by the user. */
  private _getPointerPositionOnPage(event: MouseEvent | TouchEvent): Point {