Synergy 3: Sharing Single Monitor with KVM

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I recognize that my setup is a bit of an edge case, and although clunk, sharemouse works with this setup. I'm Currently testing Synergy 3 RC2 with the demo.

Background: I have a mac and a windows machine sharing a monitor, and a laptop to the left of the monitor. I use a hardware KVM to switch between the machines, which gives me two monitors when I switch to the laptop. This KVM also switches my keyboard and mouse.

Is it possible to have two machines share the same monitor in the "Screen layout" page? In sharemouse, I can combine them and use hotkeys to switch which one is active, and this allows me to move the mouse from my windows/mac monitor to my work laptop. I would like to do the same with Synergy. (I'm interested in switching because sharemouse goes into demo mode if the "server" computer is asleep for too long, it is very annoying)

This below image is the best I can do with Symless, but with this I can only move the mouse back to the right monitor with the top half of the monitor for windows and the bottom half for MacOS.

 

This is how it looks in sharemouse. Notice the "link" icon on the right monitor and the profiles on the top right for switching the active desktop. Switching the active desktop profile switches which monitor the mouse will go to when moving across the boundary. 

 

ShareMouse's problem is that it is clunky to switch the active desktop profile. It requires a hotkey to switch it, and it would be better if it would automatically detect which one was active based when the keyboard/mouse switches to another device. (it is able to detect when the laptop is using both monitors, just not when the monitor switches between the Mac Mini and Windows machine).

 

Synergy 3 looks really good, but unfortunately it won't work with my setup without the ability to share monitors between devices and a way to switch which device is active with the keyboard and mouse (automatically preferred)