Code

// we need the following point to remain where it is after zoom
Point2D zoomHere = ...;
Point zoomHereScreenPoint = fc.DocToDevice(zoomHere);

// the zoom method zooms relatively to the scroll position
fc.setZoomFactor(...);

// check how much the document point has been offset by the zoom
Point2D afterZoom = fc.deviceToDoc(zoomHereScreenPoint);

// add the offset to scrollX/scrollY to make the initial document point coincide with the on-screen zoom center point
fc.setScrollX(fc.getScrollX() - zoomHere.x + afterZoom.x);
fc.setScrollY(fc.getScrollY() - zoomHere.y + afterZoom.y);