Effect preview is not interactive

How to reproduce:

1. Create a New Effect
2. Add a Drop Shadow node
   1. Change its vertical offset to minimum/maximum value
3. Zoom in and zoom out.

Description

The effect preview is not interactive, therefore it's not possible to zoom in to specific parts of the test image. In that case, it's not possible to zoom in to the top / bottom of the test image in order to investigate the shadow above / below the object.

Expected behavior

It's possible to move around in the effect preview using mouse, and/or zoom in to the place pointed with a cursor using mouse wheel.