Zooming Inside a Scrollpane

In JavaFX if you want the user to be able to zoom the contents inside a scrollpane here’s a small gotcha that you have to be aware of: to accomplish this you must wrap the contents of the scroll node inside a group so that the visual bounds (not the layout bounds) are used for layout calculations.

Scrolling can than be attained by setting a scaling transform on the contents of the Scrollpane and adjusting the scale value to meet the specified zoom level.

Here’s a small snippet of code to illustrate how you could do it:

public class ZoomableScrollPane extends ScrollPane{
  Group zoomGroup;
  Scale scaleTransform;
  Node content;
  (…)
  public ZoomableScrollPane(Node content)
  {
    this.content = content;
    Group contentGroup = new Group();
    zoomGroup = new Group();
    contentGroup.getChildren().add(zoomGroup);
    zoomGroup.getChildren().add(content);
    setContent(contentGroup);
    scaleTransform = new Scale(scaleValue, scaleValue, 0, 0);
    zoomGroup.getTransforms().add(scaleTransform);
    (…)
  }
  (…)
}