I want to create a 'desktop zoom' for use with xfce using xrandr

Normally I work with a scaled desktop: at start of session I do on my 1920x1080 laptop screen:

xrandr --output LVDS1 --scale 1.3x1.3 --panning 2496x1404

giving me a slightly larger desktop.

Now in my 'zoomin' button which is supposed to zoom in one step, I do something like

xrandr --output LVDS1 --scale 1.17x1.17 --panning 2496x1404

so I can move around the same desktop showing an enlarged area . I want to implement a button that
zooms in steps. But then I need to know the current scale factor or size of the viewport. But I cant seem to
find that as output of xrandr. Am I missing something?