Method _getPointerPositionOnPage

src/cdk/drag-drop/drag-ref.ts:1269–1298

Determines the point of the page that was touched by the user.

(event: MouseEvent | TouchEvent)

  /** Determines the point of the page that was touched by the user. */
  private _getPointerPositionOnPage(event: MouseEvent | TouchEvent): Point {
    const scrollPosition = this._getViewportScrollPosition();
    const point = isTouchEvent(event)
      ? // `touches` will be empty for start/end events so we have to fall back to `changedTouches`.
        // Also note that on real devices we're guaranteed for either `touches` or `changedTouches`
        // to have a value, but Firefox in device emulation mode has a bug where both can be empty
        // for `touchstart` and `touchend` so we fall back to a dummy object in order to avoid
        // throwing an error. The value returned here will be incorrect, but since this only
        // breaks inside a developer tool and the value is only used for secondary information,
        // we can get away with it. See https://bugzilla.mozilla.org/show_bug.cgi?id=1615824.
        event.touches[0] || event.changedTouches[0] || {pageX: 0, pageY: 0}
      : event;

    const x = point.pageX - scrollPosition.left;
    const y = point.pageY - scrollPosition.top;

    // if dragging SVG element, try to convert from the screen coordinate system to the SVG
    // coordinate system
    if (this._ownerSVGElement) {
      const svgMatrix = this._ownerSVGElement.getScreenCTM();
      if (svgMatrix) {
        const svgPoint = this._ownerSVGElement.createSVGPoint();
        svgPoint.x = x;
        svgPoint.y = y;
        return svgPoint.matrixTransform(svgMatrix.inverse());
      }
    }

    return {x, y};
  }

  /** Gets the pointer position on the page, accounting for any position constraints. */
  private _getConstrainedPointerPosition(point: Point): Point {