How to define voronoi polygon buffer extend in QGIS from layer extend

Question

I'm using QGIS (2.8.1) Voronoi Polygons Algorithm and I would like to extrapolate them to a polygon layer extend. In order to do this, the tool opens a window asking me to enter a number or expression (s. image) and proposing the x min/max and y min/max coordinates of all layers. What would a formular look like that covers the extend of a layer? (What do I have to enter in the field?)

Answer 1

If the 2.8 behaviour is the same as current (3.2 / 2.18) behaviour, you can only specify an increase in percent (a number) of the extent of the input layer. So to achieve what you want, you will have to choose a buffer percentage that is large enough to cover the other data set's extent, and then clip the result using the extent of that layer.