PDFView - Zoom to Rect

I am using PDFTron's PDFViewer control and want to call SetZoom factor
to implement 'zoom to rectangle' functionality.

What is the meaning of x,y paramater in SetZoom method?

SetZoom(x, y, zoom) sets the zoom factor to a new value using the given
pixel coordinate (x,y) as a zoom center.

The x,y coordinate is represented in the 'screen' coordinate system.

The zoom point (x,y) is represented in the screen coordinate system,
which starts in the upper-left corner of the client window.

Calling this function is similar to the behavior of zooming on a given
point (x, y) by mouse clicking. The new view will be centered on the
clicked point at the given zoom factor.